TROPICAL HYGIENE

A HYGIENICAL ESTIMATION OF INFLUENCING OF TROPICAL CLIMATE ON THE CONDITIONS OF LIFE, CAPACITY AND HEALTH OF POPULATION.

HYGIENICAL, TOXICOLOGICAL AND EPIDEMIOLOGICAL PROBLEMS OF FEED OF POPULATION OF TROPICAL REGIONS.

ORGANIZATION AND CONDUCTING OF SANITARY EXAMINATION OF FOOD PRODUCTS AND PREPARED MEAL IN THE COUNTRIES OF TORRID ZONE. METHODS OF MEDICAL CONTROL  AFTER THE FEED OF POPULATION OF COUNTRIES OF TROPICAL REGION.

Thermal interaction between the human body and the environment

In order to give a basic background of the perception of thermal comfort and the parameters that influence it, a brief description of  the  the thermal interaction between the human body and the environment (as described more extensive in ASHRAE Fundamentals, (2001)) is given.

.

The Heat Generated (M-W) is the total metabolic heat production within the body (M = metabolic rate required for the persons activity + metabolic level required for shivering) minus the energy production expended as external work done by the muscles (W). The net heat production (S) can either be stored increasing the body temperature or dissipate to the environment through the skin surface and respiratory tract.

The heat dissipation from the body to the immediate surroundings occurs by several modes of heat exchange:

• Sensible heat flow from the skin. The sensible heat exchange from the skin surface must pass through clothing to the surrounding environment (the unit that expresses the clothing insulation is clo; 1clo = 0.155m²KW^-1). These paths are treated in series and can be described in terms of heat transfer from the skin surface, through the clothing insulation to the outer clothing surface and to the environment. This heat flow is equal to the sum of convection and radiation heat transfer at the outer clothing surface. The heat losses are typically expressed in terms of environmental factors, skin temperature and skin wettedness.

• Evaporative heat loss from the skin. The evaporative skin loss from the skin depends on the amount of moisture on the skin and the difference between the water vapour pressure at the skin and the ambient environment. It is a combination of latent heat flow from the evaporation of sweat and from the evaporation of moisture diffused through the skin.

• Respiratory losses. According to ASHRAE Fundamentals, (2001), “During respiration the body loses both sensible and latent heat by convection and evaporation of heat and water vapour from the respiratory tract to the inhaled air. A significant amount of heat can be associated with respiration because the air is inspired at ambient conditions and expired nearly saturated at a temperature only slightly cooler than t_cr (temperature of core compartment)”. Respiratory heat loss is often expresses in terms of sensible and latent heat losses.

How does the human organism lose a heat?

Major part of heat loses through the skin and mucous, other part goes on heating of food, water and breathes air. Through the skin loses main heat mass: for after one authors - 85-90%, after other - even 95%, so, only 4-6% loses on heating of food, breathe air and waters.

http://www.1cro.com/medicalphysiology/chapter21/kap%2021.htm

 

Because of that interestingly will learn how the heat is lost by skin. Appear, that skin loses a heat by three ways:

•by radiation,

•taking and

•on evaporation of sweat moisture.

For data of Rubner, we can say, that man attached to light work in room conditions

•loses by radiation about 40%,

•taking - about 30% and

•by evaporation - about 20% of heat.

These ciphers are directed for orientation, and really they consider vacillate dependency on conditions.

Over the years, researchers of human comfort have established the variables that affect a human's thermal sensations and they have established the ranges of these variables within which the average person is comfortable.

Hygienic characteristic of tropic climate

 

From medico–geographical point of view, tropics are a part of the earth surface situated in equatorial (from 10 north latitude till 10 south latitude), tropical (from 10 till 20 north latitude and from 10 till 20 south latitude) and subtropical climatic (from 20 till 30 north latitude and from 20 till 30 south latitude) zones.

The most of the land belongs to tropics: almost all Africa, South Asia, south of East Asia, the most part of Latin America, Oceania. The most part of population lives in tropics and subtropics. Transitional zone adjoins to tropic zone (Mediterranean area, front and middle Asia, the south of the USA etc.) and it is characterized as tropic and mild zones from to medico –geographical point of view.

Sun is the source of heat, light and energy for the biosphere. Sun energy causes air streams and weather changing in the result, determines area climate. All organic life on the Earth is connected with solar energy.

The amount of solar energy, reaching the Earth surface depends on the geographic latitude of the locality because it determines noon Sun height above the horizon and day and night duration. If the angle of sun rays fall angle is close to 90⁰, the most radiation falls per unit of the horizontal surface and it has shorter way of penetration through the atmosphere.

Values of angles for different latitudes of the northern hemisphere during the equinox (on 21.03 and 21.09) and solstice (on 22.06 and 22.12) are shown in table 1.

 

Table 1

 

Sun angle in the noon in degrees (for northern hemisphere)

 

 

Climate classification for tropic countries:

1.     Steppe climate;

2.     Mediterranean climate;

3.     Savannah climate;

4.     Subtropical and tropical desert climate;

5.     Humid tropical forest climate.

 

Steppe climate

 

There are two steppe categories. There are steppes, which are situated in mild latitudes and steppes which are situated in tropic and subtropical latitudes along the desert periphery.

In summer time in this zone the prevalent air mass is mild zones continental air which transforms into continental tropical air. There are frequent hot air temperatures (30-40⁰) with low humidity in summer. Average temperature of the warmest month is +24⁰C (in steppe of mild latitudes), in steppes of tropical latitude it is 4-6⁰ degrees more.

In winter it is warm without frost and snow in tropic zone steppes.

It is snowy and temperature decreases to –10⁰ –20⁰ in mild latitudes steppes.

 

Mediterranean climate

 

The climate is warm, average temperature of the coldest month is 0⁰C, the warmest month temperature is +22+28⁰C. The summer is hot and dry, sometimes the temperature reaches +42+45⁰C due to hot winds (sirocco and mistral) from the North Africa deserts.

Savannah climate

 

Savannahs are widely spread in the most part of Africa and South America tropical part, in Hindustan from 22 south latitude, on the Ceylon island, Myanmar central part, Indo-China, Australia north part, Hawaii.

Savannah is tropical forest–steppe. Gross grass covering develops here at the beginning of rain periods. There are trees (evergreen and trees which drop their leaves in dry season) but they don’t form big areas.

In winter dry continental tropical air prevails, brought by trade winds, in summer there is wet air from equator. That is why wet weather with heavy precipitations is frequent in summer, the highest average temperature per month is +25…+30⁰C , but in winter the weather is dry, the lowest average month temperature is +15…..+18⁰C.

 

Subtropical and tropical deserts climate

 

The tropical desert is an environment of extremes. This extremity causes people’s life impossible because of dry sunny and hot weather prevalence. Average summer month temperature increases to +25…+30⁰C and day temperature in shadow may reach +40…+50⁰C.

Water-rich air masses are sporadic in subtropical and tropical zones deserts. Continental tropical air from trade winds loses its humidity before deserts. There are deserts of Sahara, Libyan, Nubian, Namibia, Kalahari and also Arabia, South America and central part of Australia deserts. Complete absence of cloudiness, high solar radiation amount, high air and ground temperature, dryness and high level of evaporation, limited or complete absence of water resources are common for deserts.

Average annual air temperature is higher than +18⁰C, in some places it reaches +25⁰C and more. In summer average month air temperature reaches +28…..+37.5⁰C and it is +32 C.. +36.5⁰C common in the warmest place but it can reach +40⁰C. Day temperature often reaches +40.. +45⁰C or even +50⁰C (Sahara, Death Valley). Maximum average month air temperature was +49⁰C and absolute maximum air temperature in shadow was +55……+63⁰C(Somali, Africa). During the day ground temperature may increase up to +80⁰C and at night under conditions of clear sky air and ground temperature decreases to +10….+1⁰C. In winter average month air temperature is approximately +10⁰C.

 

Tropical rainforest climate

 

Tropical rainforest climate is spread in Equatorial Africa, South America, Central America, west coast of Indo–China, south-west coast of India, Malaccan peninsula, Philippines, New Guinea and others. It is widely spread along the Congo and the Amazon rivers. Climate is hot and humid. Average annual air temperature is high (+24⁰C….+29⁰C). Important peculiarity is that average month air temperature is monotonous with little difference between the warmest (+27…+28⁰C) and the coldest (+24...25⁰C) months. Air humidity is 70-80-% and more. Under high radiant temperatures and little air movement in tropical rainforests the organism heat exchange is under great physiologic tension.

 

Climatic conditions of oceans in tropic latitude

 

Oceanic climate peculiarities are characteristics of open oceanic and sea areas, islands and seaside zones of continents where sea air masses are spread. Oceanic climate is characterized by its latitude, atmospheric circulation, warm and cold ocean streams. Low range of the fluctuations of the daily (1-3) and annual (10-12) air temperature is common for oceanic climate.

In hot regions of Atlantic, Pacific and Indian oceans there are following zones: equatorial, equatorial monsoons, tropical and subtropical. In equatorial zone climatic conditions are not very distinct from climatic conditions of tropic rainforests. Average month air temperature of the Indian ocean is +27.5...+29⁰C, western part of the Pacific ocean is +27.5….+28.5⁰C, eastern part – +24.5…26⁰C, in the Atlantic ocean in summer it is +23…25⁰C, in spring +25…27⁰C. Precipitation rate is 2 000 – 3 000 mm per year.

There are areas of equatorial monsoons (originated from Arabic “mausem” which means “season” or Urdu/Hindi “mausam”, which means “weather”) in the north and south from equatorial zone. Humid equatorial air prevails there in summer. The weather is often with high temperature (per month +25…28⁰C), frequently cloudy, great amount of precipitations. In winter there is sea tropic air from trade winds. Oceanic monsoons have great influence on the south of Asia (Hindustan, Indo-China) because they form here special climate which is characterized by rainy summer.

 

 

Hygienic peculiarities of residential areas build-up as the measure of living and working population conditions optimization in tropic regions

 

Urbanization, rural-urban migration, especially in tropical zone of developing countries, has created the global social problem. According to WHO and UNCHS information over 1 billion of population are either homeless, or live in slums which are dangerous to their health.

Among big cities one should mention Mexico City (31 million population), Sao Paolo (26 million), Calcutta, Lagos and other.

These are the disadvantages related to urbanization in hot regions of the world:

-         slums, squatter settlements, which constitute 50-75% of population;

-         overload of public transport: journey to work from slums exhausts people;

-          rate of traffic accidents mortality is 4-6 times higher than from infections;

-         traffic noise causes nervous and mental, cardiovascular disorders rise;

-         air pollution from traffic discharges causes chronic bronchitis;

-         communicable diseases rate in big cities is twice higher than in rural areas;

-         water and food supply is complicated in arid regions.

Following rules of hygiene in city build-up is of great importance as a measure of living conditions optimization in these regions.

Hygienic peculiarities of urban build-up in hot regions are:

-         functional zoning of city areas – residential zone, industrial zone, communal–depot zone, traffic, recreational (rest zone), waste collection and disposal zones, taking into account the wind rose, site landscape, level of underground water, usage of forest areas, planting of greenery in the streets , flooding preventon measures, creation of open water reservoirs, fountains in recreational areas.

Creation of favourable microclimate conditions in residential and industrial premises in tropical regions is achieved by:

-   premises windows aspect: in the equatorial zone – northward and southward (long premises – parallel to the equator to decrease direct insolation), in subtropical zones of the northern hemisphere - south-eastern – south-western (premises length should be oriented along to heliothermal axis);

-   wall thickness increasing to 0.5 m and more, using bricks, high porous concrete, clay, high building increasing, galleries equipment, balconies. Roofs should be made of heat-proof materials and project for 2-3 m out of wall borders, double or isolated ceiling, floor should be made of concrete or stone slabs. There should be awnings over windows, gratings, venetian blind, through air ventilation due to double–sided windows location, natural and artificial ventilation, air conditioning.

 

 

 

METHODS OF EQUIVALENT-EFFECTIVE AND RESULTANT TEMPERATURES DETERMINATION

 

The equivalent-effective temperature (ЕЕТ) is a contingent-numeral determination of human subjective heat feeling (“comfortable”, “warm”, “cold” ect.) under different ratios of temperature, humidity, air movement, and the resultant temperature (RТ) – also the radiant temperature. These standard units of ЕЕТ and РТ correspond to temperature of still (0 m/s) 100 % water saturated air. The feeling of the heat or cold results from the different variations of these EET and RT standard units.

ЕЕТ and РТ were elaborated in special box conditions with different ratio of microclimate characteristics and drawn up in tables and nomograms.

At first, temperature, humidity, air movement are measured for EET determination in the certain room. The value of EET is determined in accordance to these data (see table 4) and an appropriate conclusion is drawn. Usage of this table is simple: ЕЕТ is determined at the intersection of air temperature value (first and last columns), air movement and humidity (at the top of the table).

The equivalent-effective temperature is determined at the intersection of dry-bulb (at the left) and wet-bulb (at the right) thermometers of the psychrometer and the air movement (m/min on the curved lines) on nomogram (see fig. 1).

Fig. 1. Nomogram of the effective temperature determination

 

The following actions should be performed to find out the resultant temperature from the nomogram (fig. 2). First, the point, where the air movement corresponds to the air temperature (by dry thermometer) is found. Then, a line starting from that point to the radiant temperature value is drawn, and from the point, where this line and the temperature scale to the right intersect, another line is drawn – to the value of the absolute air humidity (right scale). The resulting temperature value will be at the intersection of the last line and the nomogram curves.

 

air movement, m/s                                                         а

air movement, m/s                                          b

Fig. 2. Nomogram of the resultant temperature determination

(a – during light work; b – during hard work)

The example of the RT determination is shown on the fig 8.2. with dotted lines.

Table 4

 

Normal scale of the effective temperatures for the averagely dressed people during light work

 

 

Comment. Relative air humidity is shown in percentage.

 

Methods of the assessment of human heat balance by calculation of heat emission

 

the assessment of human feeling of the heat/cold is performed comparing the heat production during work and heat emission. heat emission is calculated as a sum of the irradiation, conduction and water evaporation.

The basic data are:

a) the human heat production in a calm state accounts to 0.8 – 1.5 kcal (3.34 – 6.27 kj) per 1 kg body weight per 1 hour, during hard work – 7-9 kcal/kg×h;

b) the body surface of “average” human (170 cm of height and 65 kg of body weight) is approximately 1.8 m² (see table 5);

c) 100% of the body surface takes part in heat emission by conduction and sweat evaporation;

d) 80% of the body surface takes part in heat emission by irradiation (see table 5).

40 % of the body surface takes part in heat emission by irradiation relating to the one-sided heat radiation source.

Table 5

Dependence of the human body surface on body weight

 

1. heat emission by irradiation (radiation) can be calculated using the following formula:

qirr. = 4.5×(т1 – т2) s

(1)

where: q – heat emitted by irradiation, kcal/h;

  т₁ – body temperature, °с;

  т₂ – internal wall surface temperature, °с;

  s – body surface area, m².

 

2. Heat emission by conduction can be calculated using the following formula:

qcon = 6(т1 – т2) × (0.5 + √‾v) s	(2.1)
qcon = 7.2 (т1 – т2) × (0.27 + √‾v)s	(2.2)

where : q – heat emitted by conduction, kcal/h;

   6; 0.5 – constant coefficients if air movement is less than 0.6 m/s;

   т₁ – body temperature, °с;

   т₂ – air temperature, °с;

   7.2; 0.27 – constant coefficients if air movement is higher than 0.6 m/s;

   v – air movement, m/s;

   s – body surface area, m².

 

3. The maximum amount of water evaporated from the body surface can be calculated using the following formula:

рevap = 15(fmax –  fabs) × (0.5 +√‾v)s

(3.1)

where: р_evap – water. evaporated from body surface under this conditions, ml/h;

15 – constant coefficient;

f_max – maximum humidity under skin temperature of the body;

f_abs – absolute humidity under currant air temperature.

“f_abs” – can be calculated using the following formula:

(3.2)

where: f _max– maximum humidity under air temperature, hg mm. ;

 f_rel.– relative humidity under current air temperature, %;

 (f_max –  f_abs) – physiological humidity deficit, hg mm.;

 v – air movement, m/s;

 s – body surface area, m².

Quantity of emitted heat may be calculated by multiplication of the result by 0.6 (calorie evaporating coefficient of 1 g of water). or by putting the coefficient “9” in formula (3.1) instead of “15” (0.6×15 = 9). it is necessary to remember that an adequate heat self-feeling remains stable if sweat evaporation is not more than 250 ml (it takes 150 kcal).

 

Example of the calculation:

a “standard men” (body surface is 1.8 m², height – 170 cm, body weight – 65 kg) in light clothing with body temperature of 36⁰c works physically hard (570 kcal/h) in a room. microclimate characteristics of the room are: air temperature 32⁰c, average radiant temperature 22⁰c, air movement 0.7 m/sec., relative humidity 70%. evaluate the feeling of this man. estimate the heat emission by irradiation (heat emission from 80% body surface) and conduction using the formula (1)

q_irr = 4.5(36-22)×1.8×0.8 = 90.72 kcal/h

q_cond = 7.2×(36-22)×(0.27 + 0.83)×1.46 = 160 kcal/h

For calculation of the maximum amount of water evaporated from body surface, the maximum humidity under 36° с is determined according to table “maximum pressure of water vapour at different temperatures”. maximum humidity is 42.2 hg mm according to this table.

Absolute humidity under the air temperature 32° с is determined using the formula (3.2):

f_аbs. =  = 29.5 hg mm

insert the calculation results into the formula (3.1):

р_evap =15× (42.2 – 29.5)×(0.5 = 0.83)×1.8 = 456 ml/h.

heat emission by evaporation under this condition is:

456×0.6 = 273.6 kcal/h.

calculate the total heat emission:

q = 90. 72 + 160.0 + 273.6 = 524.32 kcal.

Comparing the heat emission and heat production (570 kcal/h) for the assessment of the feelings of the human, we can conclude, that the heat production exceeds the heat emission, and thus the microclimate of this room causes the “heating”.

Comment: these calculations ignore heat emission by breathing: inhaled air heating and water evaporation from lung surface. this amount is near 15% of total heat emission in comfortable conditions. we inhale the air of certain temperature and humidity. an exhaled air is heated to the body temperature and is saturated to the 100% humidity.

Heat exchange and thermal regulation peculiarities of the organism in tropic climate

There you can find the information that in optimal microclimate heat exchange mechanisms function without physiologic tension. Heat exchange is performed through the breathing – 12-15% (heating of expired air and moisture evaporation out of lungs and mucous surface) and through skin: 45-47% by radiation, 28-30 % by conduction (convection and conduction), 15-18% - by sweat evaporation from the skin surface.

In tropic climate air temperature and radiant temperature from the Sun, heated soil surface and other solid surfaces (walls, metal cars and others) often can be higher than human body’s temperature, due to this human body can’t loose heat by radiation, convection or conduction, and on contrary due to these mechanisms it can get additional heat. The only mechanism of heat exchange and heat balance is heat output by evaporation. In dry air (relative humidity is 40%) and wind presence this mechanism works rather effective which is common for arid climate areas. Under high humidity and wind absence in humid climate areas this mechanism doesn’t work properly: sweat is excreted and flows down without evaporation. Due to this there can be overheating, heat or sun stroke, organism dehydration. Significant amount of salts, microelements and vitamins is excreted with sweat. And organism demands additional water (up to 5 –12 and more liters per day).

WHO and UN specialists have developed medical measures to control living and working conditions in tropic climate and preventive measures which are implemented in countries of this climate. Calculation methods of heat load determination and overheating prevention and its pathology are of great importance among medical measures.

Hygienic standards and calculation methods of heat load of organism in hot and tropic climate conditions

 

Maximum allowable equivalent-effective temperature (EET) indices.

 

Table 2

 

 

EET and resultant temperatures are calculated by means of tables and nomograms (“Self-training assignments” №4 topic # 8).

 

4.2.        Wet bulb globe temperature determination method and its hygienic assessment according to Yanglow and Minard (1955).

Wet bulb globe temperature (WBGT) is an integral index of environment temperature which takes into account temperature, air humidity, radiant temperature and it is calculated by the following formula (1):

WBGT = 0.1 t_dry + 0.7 t_wet + 0.2 t_bulb,          (1)

where, WBGT – is wet bulb globe temperature;

t_dry – temperature according to dry thermometer of psychrometer indices;

t_wet – temperature according to wet thermometer of psychrometer indices;

t_bulb  radiant temperature according to the black globe thermometer.

According to Yanglow and Minard (1955) if WBGT exceeds 29.4⁰C physical load for non-acclimatized people is limited. Under 31.1⁰C WBGT physical load is excluded. Under 32.2⁰C WBGT physical load is excluded for acclimatized people too.

Example 1. Dry thermometer of Assman psychrometre t_dry =35⁰C, t_wet = 28⁰C, t_bulb = 37⁰C. WBGT is:

WBGT = 0,1×35 + 0.7×28 + 0.2×37 = 28

Conclusion: human can work and perform light physical work.

Example 2: Dry thermometer index is t_dry = 38⁰C, wet thermometer t_wet = 35⁰C, globe thermometer t_bulb = 40⁰C:

WBGT = 0.1×38 + 0.7×35 + 0.2×40 = 36.3

Conclusion: under these circumstances physical work is impossible for acclimatized people too.

 

4.3.        Heat–Load Index (HL) according to Belding and Hatch calculation.

According to this method heat-load is calculated by the formula (2);

HL = М  С  R – Е_max. kcal/hour,            (2)

where: M - intensity of metabolism during work: light work –170 kcal per hour; medium - 300 kcal per hour; hard – 420 kcal per hour;

 R – heat exchange through radiation, kcal per hour;

 C- heat exchange through convection, kcal per hour;

 E_max- maximum acceptable heat loss through sweat evaporation, kcal per hour.

Loss (-) or income (+) of heat by radiation R is calculated by formula (3):

R = 11×(t_bulb - 35) kcal/hour,                 (3)

where: t_globe – mild radiation temperature  according to the globe black thermometer;

 

Losses (-) or income (+) of heat by convection is calculated by formula (4):

С = 6×v^0.6 ×(t_dry - 35) kcal/hour,                 (4)        

where: v - air movement, m/sec. (v is in the table 4.2);

       t_dry – air temperature according to dry temperature of psychrometer;

       35 – surface body temperature.

Table 3

 

v m/sec	0.05	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9	1.0
v0.6	0.17	0.25	0.38	0.49	0.58	0.66	0.74	0.81	0.87	0.94	0.99

 

Maximum heat loss through sweat evaporation (E_max) is calculated by formula (5):

Е_max. = 12×v^0.6 ×(42 - р) kcal/hour,               (5)

where: p - maximum water pressure, Hg mm under dry thermometer of psychrometer.

 

In case of wearing light clothes calculation result of heat load by formula (2) is divided by 3.

Authors recommend allowable values of heat–load index in the range of no more than 400-600 kcal per hour. It should be mentioned that with air movement increase sweat evaporation intensity increases proportionally. Thus this method is used in conditions of weak air movement.

Example: During the first part of summer (June) workers brigade is working on cotton plantation performing work of medium intensity. Metabolism intensity rate M = 300 kcal per hour. Mild radiant environmental temperature according to black globe thermometer t = 40⁰C; air temperature according to dry thermometer of psychrometer t_dry = 38⁰C; air movement v = 0.05 m/sec.; maximum air humidity according to dry thermometer (38⁰C) p = 48 Hg mm.

At first loss (-) or income(+) of heat through radiation should be calculated: R= 11×(40 - 35) = 11×5 = + 55 kcal/hour.

Then loss (-) or income (+) of heat through convection should be calculated C = 6×0.17×(38 - 35) = + 3.06 kcal/hour.

Then the maximum heat loss by sweat evaporation is calculated Е_max. = 12×0.17× (42 - 48) = - 12.24 kcal/hour.

Consequently, heat load index (HL) will equal HL = 300 + 55 + 3.06 – 12.24 = 345.82 kcal per hour, and for 6 hours of 7 hours working day (1 hour for break and lunch) the heat load will equal 345.82×6 = 2 074.92 kcal.

Conclusion: The heat stress doesn’t exceed allowable level (400-600 kcal per hour).

 

While assessing results of heat exchange of the organism in tropic climate calculation, one should mention that huge amounts of macro- and microelements are excreted with sweat, especially chlorides, potassium, magnesium and that has a negative influence on heart activity and provoke angina pectoris, cardiac infarctions incidences especially in non-acclimated people. In order to prevent these complications salt loss with sweating should be compensated by means of salt rich (fruit) beverages and diet correction.

Leading specialist of tropic medicine Givoni has developed more accurate but camber-some thermal load index calculation method. Its realization is effective if using personal computer or calculator. Thus this method can be used only if there is a computer at the chair. At chairs without computer the method is just introduced to students.

4.4. Determination method and hygienic assessment of thermal load index by Givoni.

Thermal load index allows to calculate heat amount which it is necessary to excrete from organism through sweat evaporation in heat climate or microclimate conditions.

This index is calculated by formula (6):

S = (M ± C ± R) * 1/f – E_nes* 1/f,             (6)

where:  S - thermal load index (required sweat excretion amount g/per hour);

M - metabolism intensity kcal per hour (light work- 170 kcal per hour; medium - 300 kcal per hour, hard –420 kcal per hour);

C – heat exchange through convection, kcal per hour;

R – radiant heat amount which person gets from the Sun, kcal per hour;

E_nes - required cooling swear evaporation, kcal per hour;

f - cooling sweat evaporation effectiveness.

Note. Amount of heat is added to thermal production M during calculation. This is the heat, a person gets through convection from hot air of deserts, tropics (C) and radiation form the Sun and locality. It should be taken away if the heat is excreted by these methods (when body’s temperature is higher then air temperature and radiant environmental temperature).

 

Convection rate is calculated by the formula (7):

C = α×v^0.3×(t_dry -35),                                (7)

where: a – coefficient which depends on clothes (see table 4.3) ;

 V – air movement, m/sec;

 t_dry – air temperature according to dry thermometer of psychrometer.

 

Value of radiant temperature R is calculated by formula (8):

,      (8)

where: K_Cl –coefficient which depends on clothes;

 K_CK_P –coefficient which depends on environment character and body position according to the Sun (see table 4.4);

 In – solar radiation intensity (for ordinary person at noon in the desert it is 1620 kcal per hour);

 a - coefficient which depends on clothes character (see table 4);

 v - air movement, m/sec.

 

The value l/f characterizes effectiveness of cooling by sweat excretion and is calculated by formula (9):

1/f = е^0.6 * (),                        (9)

where:  e^0.6 – 1.82;

   E_max – maximal evaporative air ability, calculated by formula (10):

Е_max = β ×v^0.3× (42 - р),                           (10)

where: β – coefficient which depends on clothes character (see table 4) ;

  p - maximum air humidity, Hg mm under temperature of dry thermometer of psychrometer;

  v - air movement, m/sec.

Table 4

Coefficient values depending on clothes

 

Table 4

 

Coefficients which depend on environment (K_C) and human body position according to the Sun (K_P) – K_CK_P:

 

 

Researches have confirmed the some people excrete 1 liter of sweat per hour during 8-hour shift but not more than 12 l per 24 hours. In laboratory it has been proven, that trained person can excrete to 2 l of sweat during 30 min but after this the person looses working abilities. (WHO reports series # 412, 1970 ).

Excretion of 1 liter of sweat per hour in desert conditions, the heat balance can be achieved if the heat load index will equal 600 kcal per hour with low cardio-vascular system tension and without body temperature increase. But the same sweat excretion intensity in high air humidity for a dressed person can be accompanied by great thermoregulation mechanisms tension. In such conditions only 0,5 l of sweat per hour evaporates, taking heat for latent heat of evaporation formation. (0,6 kcal per g of sweat). The rest of sweat doesn’t evaporate and moistures the clothes.

Thermal load index (TLI) by Givony can be used for physiological tension assessment under conditions when sweat excretion equals thermal stress. Higher TLI can be used for physiological tension of thermoregulation mechanisms assessment. (WHO technical report series # 412, 1970). TLI can also be used for required water volumes to restore its reserves of the organism determination.

 

HEAT TRANSFER,

 in physics, process by which energy in the form of heat is exchanged between bodies or parts of the same body at different temperatures. Heat is generally transferred by convection, radiation, or conduction. Although these three processes can occur simultaneously, it is not unusual for one mechanism to overshadow the other two. Heat, for example, is transferred by conduction through the brick wall of a house, the surfaces of high-speed aircraft are heated by convection, and the earth receives heat from the sun by radiation.

Heat Transfer Heat can be transferred by three processes: conduction, convection, and radiation. Conduction is the transfer of heat along a solid object; it is this process that makes the handle of a poker hot, even if only the tip is in the fireplace. Convection transfers heat through the exchange of hot and cold molecules; this is the process through which water in a kettle becomes uniformly hot even though only the bottom of the kettle contacts the flame. Radiation is the transfer of heat via electromagnetic (usually infrared) radiation; this is the principal mechanism through which a fireplace warms a room.© Microsoft Corporation. All Rights Reserved. 

CONDUCTION

This is the only method of heat transfer in opaque solids. If the temperature at one end of a metal rod is raised by heating, heat is conducted to the colder end, but the exact mechanism of heat conduction in solids is not entirely understood. It is believed, however, to be partially due to the motion of free electrons in the solid matter, which transport energy if a temperature difference is applied. This theory helps to explain why good electrical conductors also tend to be good heat conductors (see Conductor, Electrical). Although the phenomenon of heat conduction had been observed for centuries, it was not until 1882 that the French mathematician Jean Baptiste Joseph Fourier gave it precise mathematical expression in what is now regarded as Fourier's law of heat conduction. This physical law states that the rate at which heat is conducted through a body per unit cross-sectional area is proportional to the negative of the temperature gradient existing in the body.

The proportionality factor is called the thermal conductivity of the material. Materials such as gold, silver, and copper have high thermal conductivities and conduct heat readily, but materials such as glass and asbestos have values of thermal conductivity hundreds and thousands of times smaller, conduct heat poorly, and are referred to as insulators (see Insulation). In engineering applications it is frequently necessary to establish the rate at which heat will be conducted through a solid if a known temperature difference exists across the solid. Sophisticated mathematical techniques are required to establish this, especially if the process varies with time, the phenomenon being known as transient-heat conduction. With the aid of analog and digital computers, these problems are now being solved for bodies of complex geometry.

CONVECTION

Conduction occurs not only within a body but also between two bodies if they are brought into contact, and if one of the substances is a liquid or a gas, then fluid motion will almost certainly occur. This process of conduction between a solid surface and a moving liquid or gas is called convection. The motion of the fluid may be natural or forced. If a liquid or gas is heated, its mass per unit volume generally decreases. If the liquid or gas is in a gravitational field, the hotter, lighter fluid rises while the colder, heavier fluid sinks. This kind of motion, due solely to nonuniformity of fluid temperature in the presence of a gravitational field, is called natural convection. Forced convection is achieved by subjecting the fluid to a pressure gradient and thereby forcing motion to occur according to the law of fluid mechanics.

If, for example, water in a pan is heated from below, the liquid closest to the bottom expands and its density decreases; the hot water as a result rises to the top and some of the cooler fluid descends toward the bottom, thus setting up a circulatory motion. Similarly, in a vertical gas-filled chamber, such as the air space between two window panes in a double-glazed, or Thermopane, window, the air near the cold outer pane will move down and the air near the inner, warmer pane will rise, leading to a circulatory motion.

The heating of a room by a radiator depends less on radiation than on natural convection currents, the hot air rising upward along the wall and cooler air coming back to the radiator from the side of the bottom. Because of the tendencies of hot air to rise and of cool air to sink, radiators should be placed near the floor and air-conditioning outlets near the ceiling for maximum efficiency. Natural convection is also responsible for the rising of the hot water and steam in natural-convection boilers (see Boiler) and for the draft in a chimney. Convection also determines the movement of large air masses above the earth, the action of the winds, rainfall, ocean currents, and the transfer of heat from the interior of the sun to its surface.

RADIATION

Wilhelm Wien German physicist Wilhelm Wien won the 1911 Nobel Prize in physics. His discoveries in the field of radiation, including the laws that govern heat radiation, laid the foundation for the development of the quantum theory.© The Nobel Foundation 

 This process is fundamentally different from both conduction and convection in that the substances exchanging heat need not be in contact with each other. They can, in fact, be separated by a vacuum. Radiation is a term generally applied to all kinds of electromagnetic-wave phenomena. Some radiation phenomena can be described in terms of wave theory (see Wave Motion), and others can be explained in terms of quantum theory. Neither theory, however, completely explains all experimental observations. The German-born American physicist Albert Einstein conclusively demonstrated (1905) the quantized behavior of radiant energy in his classical photoelectric experiments. Before Einstein's experiments the quantized nature of radiant energy had been postulated, and the German physicist Max Planck used quantum theory and the mathematical formalism of statistical mechanics to derive (1900) a fundamental law of radiation (see Statistics). The mathematical expression of this law, called Planck's distribution, relates the intensity or strength of radiant energy emitted by a body to the temperature of the body and the wavelength of radiation. This is the maximum amount of radiant energy that can be emitted by a body at a particular temperature. Only an ideal body (blackbody,) emits such radiation according to Planck's law. Real bodies emit at a somewhat reduced intensity. The contribution of all frequencies to the radiant energy emitted by a body is called the emissive power of the body, the amount of energy emitted by a unit surface area of a body per unit of time. As can be shown from Planck's law, the emissive power of a surface is proportional to the fourth power of the absolute temperature. The proportionality factor is called the Stefan-Boltzmann constant after two Austrian physicists, Joseph Stefan and Ludwig Boltzmann, who, in 1879 and 1884, respectively, discovered the fourth power relationship for the emissive power. According to Planck's law, all substances emit radiant energy merely by virtue of having a positive absolute temperature. The higher the temperature, the greater the amount of energy emitted. In addition to emitting, all substances are capable of absorbing radiation. Thus, although an ice cube is continuously emitting radiant energy, it will melt if an incandescent lamp is focused on it because it will be absorbing a greater amount of heat than it is emitting.

Opaque surfaces can absorb or reflect incident radiation. Generally, dull, rough surfaces absorb more heat than bright, polished surfaces, and bright surfaces reflect more radiant energy than dull surfaces. In addition, good absorbers are also good emitters; good reflectors, or poor absorbers, are poor emitters. Thus, cooking utensils generally have dull bottoms for good absorption and polished sides for minimum emission to maximize the net heat transfer into the contents of the pot. Some substances, such as gases and glass, are capable of transmitting large amounts of radiation. It is experimentally observed that the absorbing, reflecting, and transmitting properties of a substance depend upon the wavelength of the incident radiation. Glass, for example, transmits large amounts of short wavelength (ultraviolet) radiation, but is a poor transmitter of long wavelength (infrared) radiation. A consequence of Planck's distribution is that the wavelength at which the maximum amount of radiant energy is emitted by a body decreases as the temperature increases. Wien's displacement law, named after the German physicist Wilhelm Wien, is a mathematical expression of this observation and states that the wavelength of maximum energy, expressed in micrometers (millionths of a meter), multiplied by the Kelvin temperature of the body is equal to a constant, 2878. Most of the energy radiated by the sun, therefore, is characterized by small wavelengths. This fact, together with the transmitting properties of glass mentioned above, explains the greenhouse effect. Radiant energy from the sun is transmitted through the glass and enters the greenhouse. The energy emitted by the contents of the greenhouse, however, which emit primarily at infrared wavelengths, is not transmitted out through the glass. Thus, although the air temperature outside the greenhouse may be low, the temperature inside the greenhouse will be much higher because there is a sizable net heat transfer into it.

In addition to heat transfer processes that result in raising or lowering temperatures of the participating bodies, heat transfer can also produce phase changes such as the melting of ice or the boiling of water. In engineering, heat transfer processes are usually designed to take advantage of these phenomena. In the case of space capsules reentering the atmosphere of the earth at very high speed, a heat shield that melts in a prescribed manner by the process called ablation is provided to prevent overheating of the interior of the capsule. Essentially, the frictional heating produced by the atmosphere is used to melt the heat shield and not to raise the temperature of the capsule (see Friction).

What is the heat losing way by radiation?

From physics we know, that any more heated body radiates more heat, than less heated. So, even not colliding with it, it gives to it its heat, while the temperatures of both bodies will not complete with each other.

•Man in room conditions is usually circled by objects with more low temperature, than his body, that is why takes place heat losing by radiation.

•Also heat is lost by installation. In this case a heat is lost by two ways - conduction and convection.

•Conduction is a heat transition on the strength of contiguity of objects, and also air parts from more heated to less heated. Convection is a heat transmission on the strength of mediators - air, steam, liquid, the fractions of which, heating attached to contact with more warm body, bear off heat and return it attached to contiguity with more cold objects. On the strength of temperature difference in intermediate environment, for example, in air, the convectional streams are generated.

•The third way of heat losing is evaporation of moisture.

A human skin is always covered by sweat, water of which evaporates. For this process it is necessary expenditure of warm /secretive evaporation temperature /.

http://ppo.tamuk.edu/ehs/Heat_Stress/heatstress.htm

 

HEAT DISORDERS

http://www.answers.com/topic/heat-disorders

Heat disorder results from unaccustomed or prolonged exposure to excessive heat causing the body's cooling mechanism to break down leading to damages to the body's heat regulating mechanism. Heat exhaustion and heat stroke are similar problems, but they are not the same. Heat exhaustion refers to overheating of the body due to excessive loss of fluids or in rare cases salt depletion. Heat stroke, a more severe condition that occurs when the body's thermoregulatory system stops working. Heat exhaustion is not fatal but heat stroke can be and can bring about an irreversible coma and even death.

A heat disorder results when a person engages in physical activity to the extent where the heat production within his body exceeds its ability to lose heat adequately. This results in a rise in inner body (body core) temperature to the levels at which normal body functions are interfered with. This may lead to temporary or permanent disturbances in bodily functions.

CAUSES AND THE RISK FACTORS?

Heat disorder is due to unaccustomed or prolonged exposure to excessive heat. It is more common in hot climates and results from excessive sweating, leading to loss of fluids and salts and disturbances of the electrolyte balance in the body fluids. Many of the symptoms are the same as for heat exhaustion. However, cessation of sweating, difficulty walking, disorientation, fainting or unconsciousness indicates heat stroke. The key symptom to look for is disorientation. The risk increases with inter current illnesses, such as gastrointestinal disorders where there has been a vomiting and diarrhoea. Any illness such as diabetes may make this condition more likely to occur and elderly people should be especially careful.

KNOW THE DIFFERENCE

It's important to note the differences between the three main heat related disorders. While heat cramps can be uncomfortable, they are not life threatening. Heat stroke on the other hands needs immediate medical attention. When it comes to heat, your body is like a car. If either one overheats, it can cause minor or major problems. But knowing what to do can help your body (or your car for that matter) to keep running. When a person has heat stroke, it's like a car running with almost all the water boiled out of the radiator. It's very serious, and can lead suddenly and without warning to a complete breakdown. Learn to recognize the symptoms and treat the problem accordingly.

Heat cramps - are associated with lack of fluids, high temperature, excessive salt and fluid losses due to profuse sweating when the bodies attempt to rapidly lose heat. Feeling most like a severe muscle pull, heat cramps are forceful and painful. Heat cramps, while painful, is not life threatening. It presents as intermittent muscle contractions in both the gastronomes or hamstring area (back of calves). 

Heat exhaustion - a more severe condition caused by extreme body heat. Excessive heat and dehydration can cause the body to overreact, thus raising your body temperature to over 39OC. Heat exhaustion is a serious condition and should be carefully monitored. 

Symptoms includes:

• Paleness, cool, clammy skin

• Profuse sweating with an elevated body temperature

• Extreme fatigue

• Dizziness, lightheadedness

• Nausea, vomiting

• Fainting

• Muscle cramps in the limbs, abdomen or back

• Rapid, shallow breathing

Heat stroke - is the most dangerous heat related disorder, often putting victim's lives in danger. Heat stroke is a medical emergency, anyone exhibiting the signs and symptoms should be rushed to the nearest medical facility. Heat stroke does not have to be caused by exercise or exertion. High temperatures, lack of body fluids and overexposure to the elements can all bring about heat stroke. It manifests with a body core temperature of 41OC and above.

SYMPTOMS

The key symptom to look for is disorientation. A person who is functioning well mentally isn't in danger. Someone who's "jelly brained" is in trouble and will be too disoriented to help themselves. Many of the symptoms are the same as for heat exhaustion; however, cessation of sweating, difficulty walking, disorientation, fainting or unconsciousness indicates heatstroke. The first sign to look for in a victim is red, hot, flushed skin. When the body overheats, it can go into crisis. Usually we sweat when we're hot, but when someone has heat stroke; there is no sweat, so it is critical that they receive emergency care immediately to relieve their body of heat. 

Other signs of Heat stroke include:

• Restlessness

• Anxiety, confusion, aggressive behaviour

• Red, swollen eyes

• The pulse rate increases rapidly and may reach 160.

• Fast rise in body temperature above 41OC when sweating stops and the patient feels as if burning up.

• Loss of consciousness. Survivors are likely to have permanent brain damage.

Table 1Classification, medical aspects and prevention of heat illness (from (6)) .

Category and clinical features Predisposing factors Underlying physiological disturbance Treatment Prevention 1. Temperature regulation heatstroke Heatstroke: (1) hot dry skin usually red, mottled or cyanotic; (2) t re, 40.5�C (104�F) and over; (3) confusion, loss of consciousness, convulsions, t re continues to rise; fatal if treatment delayed (1) Sustained exertion in heat by unacclimatised workers; (2) lack of physical fitness and obesity; (3) recent alcohol intake; (4) dehydration; (5) individual susceptibility; and (6) chronic cardiovascular disease Failure of the central drive for sweating (cause unknown) leading to loss of evaporative cooling and an uncontrolled accelerating rise in t re, there may be partial rather than complete failure of sweating Immediate and rapid cooling by immersion in chilled water with massage or by wrapping in wet sheet with vigorous fanning with cool dry air, avoid overcooling, treat shock if present Medical screening of workers, selection based on health and physical fitness, acclimatisation for 5–7 days by graded work and heat exposure, monitoring workers during sustained work in severe heat           2. Circulatory hypostasis heat syncope Fainting while standing erect and immobile in heat Lack of acclimatisation Pooling of blood in dilated vessels of skin and lower parts of body Remove to cooler area, rest recumbent position, recovery prompt and complete Acclimatisation, intermittent activity to assist venous return to the heart           3. Water and/or salt depletion (a) Heat exhaustion (1) Fatigue, nausea, headache and giddiness; (2) skin clammy and moist; complexion pale, muddy or hectic flush; (3) may faint on standing with rapid thready pulse and low blood pressure; (4) oral temperature normal or low but rectal temperature usually elevated (37.5–38.50C) (99.5–101.30F); water restriction type; urine volume small, highly concentrated; salt restriction type; urine less concentrated, chlorides less than 3 g/L (1) Sustained exertion in heat; (2) lack of acclimatisation; and (3) failure to replace water lost in sweat (1) Dehydration from deficiency of water; (2) depletion of circulating blood volume; (3) circulatory strain from competing demands for blood flow to skin and to active muscles Remove to cooler environment, rest recumbent position, administer fluids by mouth, keep at rest until urine volume indicates that water balances have been restored Acclimatise workers using a breaking-in schedule for 5–7 days, supplement dietary salt only during acclimatisation, ample drinking water to be available at all times and to be taken frequently during work day           (b) Heat cramps Painful spasms of muscles used during work (arms, legs or abdominal); onset during or after work hours (1) Heavy sweating during hot work; (2) drinking large volumes of water without replacing salt loss Loss of body salt in sweat, water intake dilutes electrolytes, water enters muscles, causing spasm Salted liquids by mouth or more prompt relief by I-V infusion Adequate salt intake with meals; in unacclimatised workers supplement salt intake at meals           4. Skin eruptions (a) Heat rash (miliaria rubra; ‘prickly heat’) Profuse tiny raised red vesicles (blister-like) on affected areas, pricking sensations during heat exposure Unrelieved exposure to humid heat with skin continuously wet with unevaporated sweat Plugging of sweat gland ducts with retention of sweat and inflammatory reaction Mild drying lotions, skin cleanliness to prevent infection Cool sleeping quarters to allow skin to dry between heat exposures           (b) Anhydrotic heat exhaustion (miliaria profunda) Extensive areas of skin which do not sweat on heat exposure, but present gooseflesh appearance, which subsides with cool environments; associated with incapacitation in heat Weeks or months of constant exposure to climatic heat with previous history of extensive heat rash and sunburn Skin trauma (heat rash; sunburn) causes sweat retention deep in skin, reduced evaporative cooling causes heat intolerance No effective treatment available for anhydrotic areas of skin, recovery of sweating occurs gradually in return to cooler climate Treat heat rash and avoid further skin trauma by sunburn, periodic relief from sustained heat           5. Behavioural disorders (a) Heat fatigue – transient Impaired performance of skilled sensorimotor, mental or vigilance tasks, in heat Performance decrement greater in unacclimatised and unskilled worker Discomfort and physiologic strain Not indicated unless accompanied by other heat illness Acclimatisation and training for work in the heat           (b) Heat fatigue – chronic Reduced performance capacity, lowering of self-imposed standards of social behaviour (e.g. alcoholic over-indulgence), inability to concentrate, etc. Workers at risk come from temperate climates, for long residence in tropical latitudes Psychosocial stresses probably as important as heat stress, may involve hormonal imbalance but no positive evidence Medical treatment for serious cases, speedy relief of symptoms on returning home Orientation on life in hot regions (customs, climate, living conditions, etc.)

 

http://www.globalhealthaction.net/index.php/gha/article/view/2057/2538

 

PREVENTION

It is possible to avoid suffering the ill effects of heat related disorders by taking a few simple precautions. Heat related disorders are preventable. Like many sicknesses, it's easier to take steps against it than it is to treat it. 

Acclimatisation
Acclimatisation is the ability of the body to undergo physiological adaptations so that the individual is able to cope better with the environmental and physiological heat stress. 

Hydration
The easiest way to avoid Heat stroke and other heat disorders is to keep your body well hydrated. This means drinking plenty of water before, during and after exposure to the elements. Drink, drink, drink, eight or more glasses of water a day during normal weather conditions and twice that during high heat periods and exercising or working in hot conditions. 

Clothing
What you wear can play a big factor in how your body will handle the heat. Excessive and tight clothing can contribute to dehydration by impeding evaporation of sweat. This causes the body to produce more sweat in order to cool the body and also leads to rise in body temperature. Light colored, loose fitting clothing will aid your body in breathing and cooling itself down naturally. Tight clothing restricts such a process and dark colors absorb the sun's light and heat. 

Limit Yourself
Watching how much activity you're participating in during hottest part of the days is also important. Heat stroke can set in less than an hour. If you feel yourself getting warm or lightheaded, it's best to take a time out and rest in the shade. Try to schedule your runs during the cooler hours of the day - morning or early evening.

6 DO'S FOR PREVENTION OF HEAT DISORDERS

• Do drink water until you are no longer thirsty and then a little more. Takes frequent breaks and drink plenty of cool water. Even when you're not thirsty, your body is losing fluid, which needs to be replaced.

• Do rest well before and in between strenuous exercises.

• Do loosen your clothing while resting.

• Do report sick if you are not feeling well before, after or during strenuous exercises or activities

• Do avoid exercises if medical leave is granted.

• Do remember the 7 R's of the first aid for heat disorders.

WHAT YOU CAN DO
7 R MANAGEMENT

• Recognise early signs and symptoms of heat related illness.

• Rest the victim in cool, shady environment preferably into an air-conditioned building.

• Remove all clothing to cool the body, if possible; soak the person in a cool bath.

• Resuscitate with CPR, if victim is unconscious. Contact an ambulance right away.

• Reduce the victim's body temperature as fast as possible by applying a wet towel around neck, armpit and groin or splash water on his body and fan him or her.

• Re-hydrate the victim if he is conscious, by giving plenty of fluids, taking it slowly rather than gulping it down.

• Rush the victim to the nearest medical facility. Prompt treatment is necessary to prevent rapid deterioration into coma or death.

WHAT YOUR DOCTOR CAN DO

• Treat severe heatstroke with rapid cooling by immersion in ice water /used of Body Cooling Unit (BCU) a special equipment that dispenses continuous fine sprays of water until the body temperature drops below 38OC, followed by cooling with cold wet towels under a fan.

• Give intravenous fluids to correct the salt and water balance in the body.

http://www.nmsu.edu/safety/programs/industrial_safety/heatstress_intro.htm

http://healthmagazine.ae/heat-disorders-or-heat-related-illness/

NUTRITION IN TROPICAL COUNTRY

INTRODUCTION

In the developing areas of the world, some of the greatest health problems are directly related to inadequate nutrition. These include early childhood malnutrition due to calorie-protein deficiencies as well as iodine deficiency goiter, blind­ness due to lack of vitamin A, and a host of infectious diseases made worse by poor nutrition.

Iron-deficiency anemia and dental caries, widespread disorders related to malnutrition, have neither geographic nor socioeconomic boundaries. Even in highly developed societies there may be large segments of the population in which hunger and undernutrition impair physical and men­tal performance.

Nutrition is the science of food, the materials or nutrients in food, what they do and how they interact — all in relation to health. Nutrition comes from food, good food that one enjoys (for eating has always been one of the pleasures of life), from food in variety so as to supply the more than 50 known nutri­ents that are necessary for proper nutrition, thereby providing the best of health that one's genetic or hereditary background permits.

Nutrition as a science can be regarded as the study of six main categories of food components: protein, carbohydrate, fat, minerals, vitamins, and water. The first three categories - protein, carbohydrate, and fat — are the only ones that provide calories. Protein provides 4 Calories/gm, as does carbohydrate. Fat provides slightly more than twice as much— 9 Calories/gm.

Although minerals and vitamins provide no calories, they function in the many metabolic processes whereby one obtains and utilizes energy from foods and builds and then maintains body tissues. Minerals also function as vital constituents of many body tissues. Iron is a necessary component of hemo­globin, myoglobin, and the cytochromes, and calcium and fluoride are required for sound teeth and bones.

Nutrition is important in modern health and medicine — in improving and maintaining good health and in improving poor health.

The acute and severe vitamin deficiencies as manifested by the classical nutritional diseases — scurvy, pellagra, beri­beri, and xerophthalmia are prevalent in many other parts of the world.

Rational nutrition and its provision in tropical regions

Rational nutrition and its provision in arid and humid areas with tropical climate is considered according to abovementioned natural peculiarities, social development of the countries, natural resources presence, which allow to solve economical and nutrition problems. For example countries of Middle East are rich with oil and despite the Arabian peninsula desert climate they trade and can receive food products from other countries. Due to these circumstances, the qualitative and quantitative sufficiency of population nutrition is satisfied.

Countries with dry climate which don't have considerable natural resources can't effectively solve the problems of sufficient nutrition for their population (e.g. Ethiopia).

Local peculiarities of food production also influence quality and quantity of nutrition. In dry regions, savannah, half-deserts, cattle-raising is spread thus one side nutrition of cattle origin food is used. In other, humid regions, food of plant origin prevails. Ethnic and religious traditions also play an important role in nutrition of certain countries’ population.

From the "Hygiene of nutrition" section (topic № 23) it is known that rational nutrition is nutrition which provides normal organism growth and development, its high working ability, resistance to negative environment factors influence.

Conditions of rational nutrition are the following:

-         energetic value of food intake. It means correspondence to organism energy expenditure, including undigested part of food (in middle climate this part is 10%, in tropical climate it is considerably more);

-         quality value of dietary intake, which means presence of all substances in necessary amount and their balance;

-         rational diet. It means correspondence of food intake to biological rhythms (food intakes in certain time of the day). Also the certain number of food intakes, intervals between them, balance between the values of different food intakes during the day;

-         enzymatic constellation. It means correspondence of food products quality to enzyme ability of individual digestive system (quality of culinary processing, condition of food intake, spices, and other factors, that make the food easy for digestion and assimilation).

- epidemiological and toxicological food safety which means the absence of infectious organisms, helminthes and poisoning substances in toxic concentrations;

According to WHO data energetic and quality nutrition value of some developing countries population doesn't correspond to physiological requirements and famine is spread in some cases.

The energy and protein deficiency can cause the edematous form of starvation – Kwashiorkor, which affects children first of all. This disease affects muscles and lower extremities swell so much that toes can't be seen under the swelling. Person losses physical strength, working ability, anemia can appear.

In conditions of the total starvation, predominant energy deficiency in tropical regions may cause the cachexia, which is characterized by growth delay, severe atrophy of muscles and subcutaneous fatty tissue. Skeleton contours are seen under the skin and the head is disproportionally big.

In tropical developing countries children suffer from sprue, alimentary dwarfism, after breast diarrhea, anemia, liver cirrhosis, debility.

Among vitamin deficiency diseases (hypo- and avitaminosis) there are malignant anemia, scorbutus, xerophthalmia, beri-beri, rachitis, keratomalacia, pellagra, ariboflavinosis etc..

Endemic diseases of minerals deficiency or excess amount of microelements are typical for some localities: endemic goiter, caries, teeth fluorosis, rachitis, iron deficiency and microcytic hypochromic anemia, selenodeficiency miopathy, molibdenosis, Keshan disease, alimentary selenosis etc.

On the other hand among well provided population such diseases as obesity, gout, atherosclerosis, hypertension, urine acid diathesis, hypervitaminosis and brain blood circulation disorder can appear.

Diseases are also connected with poverty and low culture level of population and poor food quality and they are manifested by high temperature when microorganisms reproduce and preserve their virulent properties.

The most widely spread are the following diseases bacteriological, amoebic dysentery, typhoid fever, patatyphoids, hepatitis A, poliomyelitis, zoonotic infections, food poisoning of microbial and non-microbial origin, enzymopathia, food allergies, bio- and geohelminthosis.

Suppressed appetite is one of peculiarities of hot climate, also there are disorders of food digestion which are caused by spices. (The supressed appetite and digestion are the hot climate particularities. That is why spicy meals with pepper and other digestive system stimulators are used.) People change their diet by taking food in the evening and in the morning instead of day time.

Hygienic characteristic of widespread food products of tropical region

Cereals are widespread among plant food products in arid and humid tropical areas. Wheat contains 10-20% of protein in cellulose, which causes bread pores; rice - 12% of proteins and cellulose - 1% and it’s used for cereals but not for bread,maize (corn) - 7% of proteins, millet, sorghum, gaoliang - 10-13% of proteins. Fungi (ergot, brand, aspergillus etc.) especially after heavy rainfalls, present in cereals may be harmful for human health and can cause micotoxicosis.

Beans are also widespread because they are rich with proteins (15-17%), fats (6%), tough cellulose and soy (18-19% fats) and peas, lentils, chick-pea etc.

Oil-bearing crops are widespread too. They are ground peas, coconut tree, rape, wild turnip/bittercress, mustard, olives, sesame, safflower, cocoa, tung-tree, cotton-plants. These plants are characterized by significant amount of polyunsaturated fatty acids – linoleic acid (33-50%), oleic acid (29-44%).

Manioc is prevalent among vegetables in tropical countries, especially in humid tropics, savannas. Weight of manioc tuber is 2 kg, it contains 24% of carbohydrates, 1% of proteins, 0.5% of fats, 3% of cellulose. Some sorts have up to 80 mg/kg poisonous cyanogenic glucosydes and may be harmful for health.

The sweet potato or yam is the second widely spread vegetable in tropics and subtropics. Its tuber weight is 4-5 kg. It contains 24% of carbohydrates, 2% of proteins, 1.5% of fats, 3% of cellulose. In the South-East Asia and Oceania, yams aregrown, which contain 29% of carbohydrates, 25% of proteins, 0.03% of fats, 1% of cellulose. There is a sago palm in Indonesia and Malaysia and starch groats as it’s made of core of its trunk. Sago contains 80% of starch, 3 % of proteins, 0.25% of fats. In hot climate regions pumpkins, melons and watermelons are widely used.

Among fruits citrus plants are widespread: oranges, tangerines, grapefruit, shaddocks, lemons, citrons, kumquats. These fruits are rich with sugar, organic acids and have significant dietetic properties.

Bananas play significant role in nutrition of tropics population because they are rich with sugar and vitamins, they contain 22-27% of carbohydrates, 1.3-1.5% of proteins, 0.1-0.6% of fats.

In arid areas of Asia, Africa, date palms are grown. They are called “desert bread” because of their nutritious properties. It contains 72% of carbohydrates, 7% of proteins, 2,5% of fats, 3-6% of cellulose, vitamins B.

In Indonesia and Polynesia bread tree and jackfruit are cultivated. They contain 19% of starch, 12% of sugar, 1.5% of proteins, 0.2-0.5 % of fats. Mango, mangosteen, tamarind, loquat are used in the South Asia; the pineapples, guava, sapota, avocado - in the Central America. All these fruits have high nutrition and taste qualities.

Full-value protein deficiency is significant disadvantage of these plants. Also they don’t contain enough essential acids, or the wrong balance between them, except soy and legumes. In case of one side nutrition with these plants and without sufficient assortment, the partial protein deficiency and anemia (due to the meat products’ hemoiron absence) develop.

  

Methods of medical control of sufficiency and safety of tropical regions’

population nutrition

 

In developed countries of tropical region medical control methods are similar to those, which are used in Europe. They are the following:

-         methods of nutritional status assessment of research population group;

-         methods of energy expenditure assessment, organism energy and necessary substances of dietary intake provision (calculations and laboratory methods of research);

-         methods of expert assessment of food products and ready meals for their freshness and safety (see chapter "Hygiene of nutrition").

In developing countries these methods are used by medical service in big cities or centers of administration. In rural regions these methods are applied but their results and implementation are not very effective.

Based on these results and according to the WHO recommendations, the Methods and measures of preservation and storage of food products in tropics are developed and introduced. They consider usage of antibiotics and preservatives etc.

Methods and measures of alimentary and foodborne infections and invasions, microbial and non-microbial origin food poisonings prevention are developed. Sanitary culture elements, sanitary education of population, prophylactic immunization (vaccination) etc. play significant preventive role.

 

Calculation methods of nutrition assessment and correction

 

4.1. Method of alimentary calorimetry by P.E. Kalmukov

This method allows to determine the total sum of energy expenditure for certain research period and to make corrections of intake in case of weight loss or excessive gain. It can be done by intake calories calculation in condition of adequate nutrition (taking into account part of ration which wasn't eaten) and with permanent body weight.

Researches are carried out for 15 days. If body mass doesn't change during this period - energy expenditure corresponds to digested food energy (10% of eaten intake isn't digested). If during this period a person looses weight, we can considerthat every 1 kg of body weight loss equals 4 100 kcal shortage for both for adults and children, and every 1 kg of weight gain equals extra 6 800 kcal for adults and 5 000 kcal - for children. These figures are called energy equivalents (EE).

During calculations it should be considered, that ideal theoretical body mass by Brock's index equals height in cm minus 100.

During nutrition correction for people with body weight loss, corresponding food amount is added to ration and for people with excessive weight, food amount is decreased but not less than by l 000 kcal (the level, at which the nitrogen balance (protein nutrition index (PNI, %) is not yet disturbed). Protein nutrition index is urea nitrogen share in general nitrogen content in urine in %.

Example 1. Adult person has excessive body mass of 10 kg, and in order to decrease it to ideal theoretical body mass he gets limited ration of l 000 kcal instead of necessary 3000 kcal per day. How long can this intake be used without pathological changes in the organism?

Calculation:    

Example 2. Person performs medium intensity physical work, and receives intake, worth 3 000 kcal, during 15 days. During this period, person looses 1 kg of body mass. How can the daily intake be optimized?

Calculation: Body weight decrease by 1 kg during 15 day means 4 100 kcal shortage. Thus, addition to the daily intake is:

Addition:  

 

4.2. Methods of proteins and fats sufficiency assessment.

Protein sufficiency is calculated using protein nutrition index (PNI) which is expressed in % corresponding to urea nitrogen correlation to total nitrogen in urine (see table 1).

Table 1

 

Fat sufficiency is calculated using the following formula:

D= M × C × 0.0632

where:    D - fats amount in g;

M- middle subcutaneous thickness in mm (it is determined under lower angle of the right scapula, on the back surface of the right shoulder and on the side surface of belly);

C - body surface in cm², determined according to the table 2.

 

Table 2

 

PROTEIN-CALORIE MALNUTRITION IN YOUNG CHILDREN

Protein-calorie malnutrition in young children constitutes the most important and widespread nutritional problem in the world today. The two main clinical syndromes are kwashiorkor and nutritional marasmus. In kwashiorkor the principal deficiency is of protein, whereas in marasmus there is an over­all deficit in food intake resulting in insufficient calories and protein. From the clinical point of view, there are many inter­mediate cases that are difficult to fit into either category; they show some of the symptoms and signs of both conditions.

Kwashiorkor and nutritional marasmus can be regarded as the two extremes of protein-calorie malnutrition of young children. However, very many cases of protein-calorie mal­nutrition are intermediate, and this has given rise to such names as "marasmic kwashiorkor" to describe cases in which kwashiorkor is superimposed on marasmus. Separate de­scriptions are given kwashiorkor and nutritional marasmus, but the clinicians must expect many cases to be intermediate between the two extremes.

Kwashiorkor

Kwashiorkor occurs mainly in children 1 to 3 years of age. It is common in many developing countries of Asia, Africa, and Latin America, but has been reported also in Europe and the United States, where it is associated with poverty.

The disease occurs in children whose diet is grossly defic­ient in protein. Often the food that the child is receiving is of a type that contains mostly carbohydrate and little protein. In many parts of the world, kwashiorkor is a disease of the weaning period when the child is taken from the breast and given a diet that is primarily starch. An adequate intake of breast milk will provide a satisfactory diet for the first four to six months of an infant's life. After that, chiefly because of reduced quantities, breast milk provides merely a useful protein-rich dietary supplement to whatever other food the child is receiving.

Important factors often implicated in the complex etiology of kwashiorkor are:

a)     The rapid growth and relatively high protein requirements of the rapidly growing young child;

b)    A protein-poor, staple food for the child, e.g. manioc, bananas, sugar

c) Poor infant-feeding practices;

d) A lack of protein-rich foods, both animals (e.g., meat, milk, fish, eggs) and vegetable (e.g. beans, peanuts);

e) Poor distribution of available food in the family (e.g., the adults and older children often get the major share of protein-rich foods such as meat);

f) Seasonal food shortages

g) Poverty and its attendant ills

h) Cultural dietary practices, including food taboos, may pre­clude the child's consumption of certain available and nutritionally desirable foods

i) Infections such as diarrhea, measles, whooping cough

 j) Ignorance or lack of knowledge on the part of parents or guardians concerning what foods are needed in the child's diet

k) Psychological factors that may affect the appetite of the child

The disease: Below are the main features of kwashiorkor:

a Growth failure is always present. If the child's age is known he will be found to be shorter and, except in cases with gross edema, lighter than normal.

b Wasting is always a feature, but it may be masked by edema. The wasting is often evident in the muscles of the arms and legs.

c Edema always occurs and is a most important feature of the disease . It may affect any part of the body. In an ambulant child, edema usually starts as a slight swelling of the feet and often spreads up the legs. Later the hands, scrotum, and face may all be affected.

d Mental changes are invariably present. The child is usually apathetic and uninterested in his surroundings. At the same time he is miserable and irritable when being moved or dis­turbed. He is unsmiling and his behavioral development is retarded.

e Hair changes are common. The hair often shows changes in texture, in color, in strength, and in ease of pluckability. The tight curl of African or Afro-American hair is often lost and the hair becomes silkier and loses its lustre. Black hair becomes brown or reddish brown. In Latin America, parallel strips of discolored hair have been labeled the "flag sign."

f Skin changes are not invariable, but if present may be very characteristic. The skin, especially of the face, may show depigmentation. In some cases dermatosis develops, especially in areas of friction such as the groins and behind the knees. Darkly pigmented patches appear and may desquamate like old blistered paint - a phenomenon that has given rise to the term "flaky-paint dermatosis." Beneath the flakes are atro-phic areas that may resemble a healing burn.

 g Diarrhea is common. Stools are frequently loose and con­tain undigested particles of food. Sometimes they are offen­sive, watery, and blood stained.

h Anemia to some degree is common in most cases of kwashiorkor. This is due in part to a lack of protein to synthesize blood cells but is frequently complicated by anemia resulting in iron deficiency, hookworm infestation, malaria, etc.

 i Hepatomegaly is due to fatty infiltration of the liver, which is always found post mortem in kwashiorkor.

 j Signs of other deficiencies are usual. There is usually some subcutaneous fat in persons with kwashiorkor; in marasmus there is usually none or very little. The degree of fat deficiency gives an indication of the degree of calorie deficiency. Lesions of the lips and mouth characteristic of vitamin B deficiencies may be seen, and xerosis or xerophthalmia due to vitamin A deficiency may sometimes be present.

Treatment: All patients with severe kwashiorkor should, if possible, be admitted to a hospital for treatment. Severity is judged by the degree of edema; the extent of dermatosis; the hemoglobin level; the severity of diarrhea, vomiting, and dehydration; the willingness of the child to feed; but above all by the general clinical condition of the patient.

Dried skimmed milk is a most satisfactory basis for treat­ment, but other protein-rich foods are effective. A mixture of dried skimmed milk, vegetable oil, and casein is ideal; if necessary the child can be given the mixture through an intragastric tube. The milk should provide about 120 calories and 7 gm of protein per kg of body weight per day. Vitamins should be given for vitamin deficiencies; it is especially important to treat any evidence of eye changes caused by vitamin A deficiency.

Nutritional Marasmus

Nutritional marasmus is com­mon in nearly all developing countries and, in contrast to kwashiorkor, is more common among children younger than 1 year, although it is not restricted to this age group. The disease is a form of starvation and therefore the underlying causes are numerous but all involve serious lack of food. In many countries nutritional marasmus is occasionally seen in grossly neglected children but may also occur secondary to such diseases as cystic fibrosis, celiac disease, or overwhelming infections.

A common cause of nutritional marasmus among peoples of developing countries is early cessation of breast-feeding. This may be due to death of the mother, failure of lactation, separation of the infant from the mother, or most commonly the mother's desire to feed her infant from the bottle rather than the breast. In this latter event she may be influenced by advertisements and the impact of alien cultures into believ­ing that bottle-feeding is superior or more sophisticated. Early cessation of breast-feeding does not of course necessarily lead to marasmus. However, a large proportion of people in developing countries do not have sufficient income to pur­chase enough milk formula to feed a baby properly. As a result, the tendency is to over dilute the mixture with water, which then fails to provide adequate calories. Similarly, few in these countries have a safe water supply or items in their homes with which to simplify the sterile preparation of bottles of formula for an infant. Combined with a lack of knowledge concerning hygiene, those problems commonly lead to the development of gastrointestinal infection, which starts the vicious circle leading to marasmus.

Other common causes of marasmus are prematurity and gastrointestinal diseases such as diarrhea or malabsorption. Many of the factors that cause kwashiorkor may also be involved.

The disease: Following are the main features of nutritional marasmus:

a Growth failure is clearly evident in all cases. If the age of the child is known, the weight will be seen to be extremely low by normal standards, and the height will also usually be below normal. In severe cases the wasting of flesh is obvious. The ribs are prominent, the face has a characteristic monkey-like appearance, the limbs are very thin, but the abdomen may be protuberant. In general, the child looks like the starved person he is.

b Wasting of muscles is extreme. There is little if any subcu­taneous fat remaining. The skin hangs in wrinkles, especially around the buttocks and thighs.

c The appetite is good. Whereas the child with kwashiorkor has anorexia, the child with marasmus frequently has a good appetite. In fact, like any starving creature, he may be rav­enous, often sucking his hands and clothing. d The mental state appears to be unaffected. Most children with marasmus appear bright eyed and alert. They are not usually disinterested or irritable, as are children with kwashiorkor.

e Anemia is usually present.

f Diarrhea is common, but is not a constant feature.

An advanced case of nutritional marasmus presents an unmistakable picture. The infant is appallingly thin but, in contrast to the rest of the body, the belly may be protuberant. The disease, unlike kwashiorkor, does not lead to edema or flaky-paint dermatosis. Hair changes similar to those seen in kwashiorkor can occur but are less common. Signs of vitamin deficiency, especially of vitamin A, may accom­pany marasmus.

Treatment: Treatment is similar to that described for kwashi­orkor, but an adequate intake of calories and protein is man­datory to allow for weight gain and growth. Therefore, if dried skimmed milk is used as the basis for treatment, vege­table oil should be added to provide calories.

Anemia, infections, diarrhea, and dehydration should be treated as described for kwashiorkor. In general, response to treatment in severe nutritional marasmus is slow, and pro­longed hospitalization is often necessary.

It is particularly important to ensure that the child is not discharged from treatment only to return to the very set of circumstances that led to the disease. Steps must be taken to ensure that an adequate diet is provided for the child after he leaves the hospital.

 

 

 

XEROPHTHALMIA AND VITAMIN A DEFICIENCY

Xerophthalmia, which is the clinical manifestation of vita­min A deficiency, is a common cause of blindness in some parts of the world, par­ticularly in Asia. It is caused by a diet deficient in vitamin A and its precursor, carotene. The disease occurs most com­monly in young children and is often associated with protein-calorie malnutrition.

The Disease

An early sign of vitamin A deficiency is night blindness (the inability to see well in dim light), which may be difficult to detect objectively, especially in young children. Although vitamin A deficiency may also cause follicular hyperkeratosis of the skin, the characteristic lesions of the disease are seen in the eye. Xeroph­thalmia usually begins with a drying of the conjunctiva, which then loses its shining luster. Thickening, wrinkling, or pigmentation of the conjunctiva may accompany this condition ofconjunctival xerosis. Another common lesion that may or may not be present is Bitot spots - usually small, foamy, oval or triangular plaques situated on the bulbar con­junctiva. The spots are nearly always bilateral, temporally situated, and are sometimes associated with conjunctival xerosis.

The drying of the eye may then spread to the cornea, which develops a lusterless and rough appearance termed corneal xerosis. If the disease progresses, corneai ulceration may de­velop with loss of corneai substance. At this stage, there are often no signs or only mild signs of reaction or redness due to inflammation. If the condition is not treated, a softening necrosis ensues, leading to deformation and later to destruc­tion of the eyeball. The process, known as keratomalacia, is often rapid — the cornea "melts" away, often with loss of vitreous fluid and sometimes with extrusion of the lens.

Prevention and Control

The prevention of xerophthalmia in children at risk depends on a diet rich in carotene or vitamin A and on the control of associated diseases such as protein-calorie malnutrition, measles, and diarrhea. In the meantime, certain other measures may be effective and feasible:

a Fortification of suitable foods with appropriate doses of vitamin A.

Dietary Sources: Vitamin A itself is found only in animal products, and the main natural sources are butter, eggs, whole milk, liver, and some fish.

Many plant foods contain carotene. Good sources are dark-green leafy vegetables and various pigmented fruits and veg­etables such as tomatoes, carrots, sweet potatoes, pumpkin, and papaya. Yellow corn is the only commonly eaten cereal that contains carotene. Red palm oil, which is produced and eaten in many tropical countries, is an extremely rich source.

b Periodic massive-dose programs. Vitamin A, being a fat-soluble vitamin, is stored in the liver. In a number of coun­tries, susceptible children are periodically given massive doses of vitamin A to prevent xerophthalmia.

 

THIAMIN DEFICIENCY SYNDROMES

Beriberi: The Disease

Beriberi is caused by a deficiency of the B vitamin thiamin, also known as B₁, when the ratio of its intake to the number of calories obtained from carbohydrate is low. The disease occurs predominantly among rice-eating peoples of the world because of their use of refined or polished rice.

From a clinical viewpoint, there are various ways to classify beriberi. Here it will be grouped into three forms: (1) wet beriberi, (2) dry beriberi, and (3) infantile beriberi. These three clinical forms of the disease have many different features and yet appear to be caused by the same dietary deficiency and occur in the same endemic areas.

Early clinical features common to both wet and dry beri­beri: Both wet and dry beriberi usually begin in a similar mild way. The person tires easily, his limbs feel heavy and weak, and he may get a mild degree of swelling around the ankles. There may be numbness and a feeling of "pins and needles" in the legs, as well as occasional palpitations of the heart.

Dietary sources: Thiamin is found in foods of both animal and vegetable origin. The richest sources among commonly eaten foods are pork, whole-grain and enriched cereals, and the seeds of legumes. Green vegetables, fish, meat, fruit, and milk all contain useful quantities. In cereals, thiamin is present mainly in the germ and outer coat of the seed, and much of the vitamin is lost if cereals are milled and refined.

Several antithiamins have been described. Two are thermo-labile, and they catalyze the breakdown of thiamin. The first, thiaminase I, is found in the viscera of fresh-water fish and in microorganisms, whereas thiaminase II is found only in microorganisms. Thermostable thiamin antagonists have been found in plants and animal tissues.

PELLAGRA

The disease is associated with a corn (maize) diet and is primarily due to a dietary deficiency of niacin, one of the B-complex vitamins. Although there is more niacin in corn than in some other staple foods, the vitamin is evidently not completely uti­lized, most likely

                         

because it is in a bound form unavailable to the body. The human body can convert the amino acid tryptophan into niacin, so a high-protein diet rich in tryptophan will help prevent pellagra.

To the medical student, «the Four Ds» - dermatitis, diarrhea, dementia, and death, portray pellagra. The disease is most often diagnosed from the characteristic appearance of the skin lesions. These lesions are often symmetrical in appearance and occur on areas of the body exposed to sun­light such as the face, the neck, and the forearms. In whites, the skin lesions at first resemble the erythema of sunburn. In blacks, there is a hyper pigmentation. The affected areas become dry, scaly, and cracked, and if the condition progresses desquamation commonly occurs. There may be cracking and fissuring, and occasionally the skin becomes blistered. In persons who usually wear open-neck shirts, the upper chest and lower neck are affected: the lesion is known as Casal's necklace.

Digestive symptoms include abdominal pain and diarrhea. Frequently, the tongue and mouth are sore, and angular sto­matitis and cheilosis, usually associated with riboflavin deficiency, sometimes occur. The tongue is often red, smooth, and raw looking.

Dietary sources: Niacin is present in many foods of vegetable origin, and niacinamide is present in most foods from animal sources. Particularly rich are lean meat (especially liver), peanuts, yeast, and cereal bran or germ. Beans, peas, and other legumes are good sources, but starch roots such as potatoes and cassava (manioc, yucca), common vegetables and fruits, and milk are all poor sources of the vitamin. Like other B vita­mins, the main source in the diet is frequently the cereal staple consumed. Whole-grain or lightly milled cereals con­tain more niacin than do refined cereal grains and flours. Accumulating evidence suggests that part of the niacin in certain foodstuffs, especially cereals, is not available. Pre­sumably, it is bound in a nonusable form.⁶⁹ Niacin is now often added to many manufactured food products, especially those made from cereals.

SCURVY

Scurvy is a rare disease today. It results from a deficiency of vitamin C and usually occurs only after considerable time in persons on a diet containing very little fresh fruit or vege­tables. Daily intakes of vitamin C considerably less than the recommended allowances, even for periods of several months, usually do not result in scurvy.

Vitamin C is necessary for the formation and healthy up­keep of intercellular material. In scurvy, the walls of the capil­laries lack solidity and become fragile, resulting in hemor­rhage from various sites.

The Disease

The following symptoms and signs characterize scurvy:

a Tenderness of the extremities, muscle weakness, and sup­pressed appetite may be evident.

b Gums become swollen and bleed easily; teeth may be­come loose.

c Hemorrhages of a petechial type often occur in the skin.

d Hemorrhages in other areas may manifest themselves as nose bleeds, hematuria, melena, splinter hemorrhages below the nails, and painful subperiosteal hemorrhages.

e Delayed healing of wounds and heightened risk of infec­tion may occur.

f Anemia and shortness of breath may be noted.

A patient with scurvy and some of the above symptoms and signs, though not appearing very seriously ill, may sud­denly collapse and die of cardiac failure.

Dietary sources: Vitamin C is less widely present in foodstuffs than are the other important water-soluble vitamins. The main source is from citrus fruits, juices, tomatoes, and other fruits and vegetables. Eggs, meat, and fish are rather poor sources, as is milk after pasteurization. Dried cereal grains and the seeds of legumes, unless they are sprouting, are devoid of vitamin C. Vitamin C is often added to many beverages and some foods, which are so labeled.

RICKETS AND OSTEOMALACIA

In both rickets and osteomalacia, there is a lack of calcium retention in the skeleton. The conditions are, however, due mainly to a deficiency of vitamin D and not of dietary cal­cium. Vitamin D is obtained both from the diet and from exposure of the skin to sunlight. The average unsupplemented diet contains only relatively small amounts of vitamin D, but nowadays-young children add the vitamin to many-processed foods.especially those commonly consumed. Vitamin D deficiency is therefore uncommon in children and is very rare in adults in many countries.

Rickets - The Disease

Unlike the child with any of a number of other deficiency diseases, the child with rickets often has the superficial appearance of being plump and well fed. The child's appear­ance frequently gives the mother a false sense of security. The story has often been told of the rachitic child winning the baby show because it appeared so fat and well nourished. The child, however, tends to be miserable, and closer examination will reveal the flabby toneless state of the muscles. Another feature is the general impairment of normal development. The child is frequently late in reaching all the milestones in his early life; he is slow to learn, to sit, to walk, and to get his teeth. Other generalized signs include gastro-intestinal upsets and excessive sweating of the head.

The main signs of the disease —those by which the diag­nosis of rickets is made — are the skeletal changes. One early feature is swelling of the epiphysis of the long bones. This may first be found at the wrist, where the radius is enlarged. Another classical site is at the costochondral junctions, where swelling produces the bead-like appearance that has been called "rachitic rosary." Deformities of the chest lead to the formation of Harrison's sulcus and pigeon breast. Swellings of the epiphyses of the tibia, fibula, and femur may also be seen.

In young infants, the first sign of rickets is often cranio-tabes, which consists of areas of softening of the skull, usually affecting the occipital and parietal bones. There is also de­layed closing of the anterior fontanel. In severe rickets there may be bossing of the skull.

When a child with rickets begins to stand and walk, he often develops new deformities because of the soft, weak character of the bones. The commonest deformity is bowlegs; knock-knees are seen less frequently. More serious, however, are spinal deformities that lead to kyphosis. Changes in the pelvis, though often not obvious, may cause the woman who had rickets during her childhood to have difficulty during childbirth.

Tetany due to a reduction in the level of serum calcium sometimes occurs. It presents an unmistakable picture with spasm of the hands, the thumb being drawn into the palm.

Treatment: The basis of treatment is the provision of ade­quate quantities of vitamin D and at the same time ensuring an adequate intake of calcium.

Dietary sources: Vitamin D occurs naturally only in the fat of certain food products of animal origin. Eggs, cheese, milk, and butter are fairly good sources. Meat and fish contribute small quantities. Fish-liver oils are very rich in vitamin D (and vitamin A), but the amounts vary.

Osteomalacia — The Disease

Osteomalacia is the adult counterpart of rickets and has the same general causes. It occurs much more frequently in women than in men. It is most common in women on a poor diet who have been depleted of calcium by many years of pregnancies and lactation, who get very little vitamin D in their diet, and who are protected from the sun by their cloth­ing and confinement indoors.

Pain occurs in the bones of the pelvis, lower back, and legs. Tenderness may be elicited by pressure on the affected bones. Deformities occur later, especially in the pelvis and spine. The patient may walk with his feet widely spaced and mayappear to waddle. Spontaneous fractures often are a compli­cation of severe osteomalacia. In some cases, tetany develops and may be seen as involuntary twitchings of the muscles of the face and as carpopedal spasms.

IRON-DEFICIENCY ANEMIA

Iron deficiency is one of the most common nutritional de­ficiencies in the many country. It occurs most frequently in

        infants beyond six months of age,

        in adolescent girls, and

        in women of childbearing age.

Iron absorption is influenced by many factors. In general, only about 10 % of dietary iron is believed to be absorbed. The adult male loses only about 0,5 to 1,0 mg of iron daily; his daily requirement for iron is therefore about 10,0 mg/day. On an average monthly basis, the adult premenopausal woman loses about twice that amount. Similarly, iron is lost during childbirth and in lactation; pregnant women and growing children need additional dietary iron.

The availability of iron in foods varies greatly. In general, heme iron is well absorbed from foods of animal origin (meat, poultry, and fish), but the iron present in vegetable products, including cereals such as wheat, corn, and rice, is poorly ab­sorbed. A mixture of foods consumed together may modify these differences. It is well known that phytates and phosphates, present in cereal grains, inhibit iron absorption. On the other hand, protein and ascorbic acid (vitamin C) enhance iron absorption. Recent research has shown that ascorbic acid mixed with table salt and added to cereals will increase the absorption of intrinsic iron in cereals twofold to fourfold. The consumption of vitamin-C-rich foods such as fresh fruits and vegetables with a meal may there­fore promote iron absorption. Egg yolk impairs the absorp­tion of iron, even though eggs are one of the better sources of food iron.

In the adult, iron deficiency is frequently associated with blood loss. In many parts of the world, excessive blood loss is associated with hookworm infestation, which can lead to severe iron-deficiency anemia. Increased requirements for iron are also associated with growth, iron being required for all cells and particularly for the increase in blood vol­ume. Iron deficiency is frequently encountered in infants, especially in those born to anemic mothers. The normal infant is born with iron stores, but milk is a very poor source of iron. Supplemental iron-rich foods or formulas are there­fore indicated to prevent anemia in the latter part of infancy or early childhood. Anemia and iron depletion is common in adolescent girls, who bear the combined stress of growth and menstruation. Pregnancy also imposes the stress of fetal growth combined with an expansion of the blood volume. Women with poor dietary habits often enter pregnancy with reduced iron stores.

Anemia is known to cause various symptoms such as tiredness, weakness, and dyspnea on exertion; when severe, ane­mia may lead to tachycardia, palpitations, and edema.  Iron deficiency may also impair humoral antibody response.

Sources of iron: Iron is present in a variety of foods of both plant and animal origin. In many foods there is considerable variation in the value of iron content, depending on the soil and conditions in which the food is raised. Rich food sources for iron include meat (especially liver), egg yolk, and pulses such as beans and peas. However, many other common foods such as green leafy vegetables, whole-grain and enriched cereals, vegetables, and fish are also good sources of iron. Milk, both human and cow's, contrary to the notion that it is the "perfect food," is a poor source of iron.

ENDEMIC GOITER

Goiter is the name used for any swelling of the thyroid gland. When it occurs sporadically it may be due to any of various causes not related to diet. However, where goiter is common or endemic in a district or in a community, the cause is usually nutritional, due to a lack of the mineral nutrient iodide.

In endemic goiter areas, many people have some enlarge­ment of the thyroid gland and a smaller number have large and obvious swellings of the neck.

By far the commonest cause of endemic goiter is a deficiency of iodide in the diet of those affected. The amount of iodide present in soil varies from place to place, and the soil content affects the quantity both in food grown and in the water sup­ply of the area. Seafood’s such as fish, shellfish, and seaweed are rich sources of iodide. Endemic goiter areas are usually far from the sea.

The thyroid gland requires iodide to produce thyroxine, which contains 64% iodide. When iodide is deficient, the gland enlarges to compensate for the difficulty in producing thyroxine. This basically is the mechanism at work in goiter due to iodide deficiency.

Goiter is more common among females, particularly at puberty and during pregnancy. The enlargement of the gland may be smooth and is then said to be a colloid goiter, or it may be lumpy and is then called an adenomatous or nodular goiter.

Cretinism in children occurs most commonly in endemic goiter areas and is usually due to severe iodide deficiency of the mother. The infant might appear normal at birth but is slow to develop, small in size, mentally dull, and has thick skin and characteristic facial features such as a depressed nose and, often, a protruding, enlarged tongue. Deaf mutism and mental retardation are common among the children of mothers with enlarged thyroid glands.

Prevention of Endemic Goiter

Where goiter is prevalent it constitutes a public health prob­lem and should be tackled as such. The most satisfactory measure is the addition of iodide to all salt sold in the area. Use of the salt will reduce the size of many existing goiters and will prevent most goiters from developing in the future.

Sources: Iodide is present in rocks and soils, but through the ages much has been washed into the sea. Man gets his iodide from food and from water, the iodide content of which varies according to the iodide content of their source. Seafoods on the whole are rich in iodide; dairy products, eggs, and some vegetables may also be good sources.

DENTAL CARIES

Dental caries is the most widespread disease in the world. Many nutrients are necessary for the development of the teeth and their surrounding structures.

        Vitamin A is impor­tant for normal bone growth.

        Deficiency of vitamin C influence on the soft supporting tissues of the teeth.

        Protein is also essential for the normal devel­opment of the teeth and supporting tissues. Vitamin D, calcium, and phosphorus, which are important in bone development, are also essential to the development of teeth.

        However, fluoride is the single most important mineral nutrient in relation to dental caries.

Deficiency of this microelement (less than 0,5 mg/l of water) in combination with other factors (not rational feeding, bad conditions of work and living) causes teeth caries.

 Teeth caries helps development of other diseases in oral cavity (tonsillitis, rheumatoid condition), disturbance of food digestion etc.  

Mechanism of anti-caries fluoride action is that during its interaction with mineral components of bone tissue and teeth there are formed bad-soluble connections. Fluoride also helps formation of calcium phosphate, which conditions processes of demineralization in starting caries process. In mechanism of anti-caries action of fluoride plays an important role such a thing that it acts on enzyme systems of teeth platelets and bacteria of saliva. This biological speciality of fluoride was a scientific basis for finding of effective method of caries prophylaxis – fluoridation of drinking water.