Dinesh Lathia
DINESH LATHIA is head of the Department of Nutrition Physiology, Fachhochschule Niederrhein, Mönchen-Gladbach, Federal Republic of Germany. Work on this article was assisted by the graduate thesis research of A. Bremekamp and D. Schroeder.
During the last 30 years, extensive research has gone into the influence of heat and humidity on the physical performance and nutritional requirements of people living and working in the tropics.
Although many factors affect the work capacity of tropical labourers, research results indicate the overriding importance of proper nutrition for optimum efficiency.
Manual and forest workers in many tropical countries are sometimes given an extra ration of sodium chloride in tablet form to compensate for sodium depletion from heavy sweating, and to prevent possible heat stress. But despite numerous research efforts, the value of such salt supplementation remains uncertain because of the highly contradictory nature of the results. Recent studies suggest that salt overloading through uncontrolled use of salt tablets by persons undergoing heat acclimatization may lead to serious potassium depletion.
The diet in Southeast Asia and in many other developing regions consists mainly of carbohydrates, e.g., rice, with a small amount of protein, vegetables and fruit. Rice contains only small amounts of potassium. This potassium can be lost quickly under heavy sweating and heat stress, possibly leading to hypokalaemia.
The purpose of this study is to discuss the pros and cons of salt supplementation to manual workers in the tropics. An attempt has also been made to summarize the results of recent research work on potassium depletion and protein malnutrition and their effect on workers' performance.
MANHANDLING TIMBER IN ECUADOR the climate . . . the diet . . . the work
Electrolytes
The electrolytes sodium and potassium are essential minerals for the normal growth and maintenance of the human being. They make up the largest quantity of dissolved materials in the body fluids and are important contributors to intra- and extra-cellular osmolarity. Sodium and potassium are also responsible for the electro-physiological processes in the cells.
Sodium depletion is generally associated with dehydration, when extra-cellular fluid is reduced and the haematocrit value is higher than average due to low blood volume. Further, blood pressure is low and the pulse is rapid. Thirst is often absent, although the mouth is dry. The characteristic symptom is cramping of the muscles of the extremities and abdomen. This is particularly common to miners who work in hot pits. Headaches, nausea, diarrhoea, mental apathy and loss of appetite may also be present.
It is now also well recognized that sodium depletion may occur without water depletion, in a condition called "water intoxication." This occurs when thirst brought on by heavy sweating is quenched by water without the addition of salt.
The main symptoms of potassium deficiency are irritability, muscular weakness, mental confusion, dilation of the heart and periodic paralysis.
It is likely to develop into chronic wasting diseases in conjunction with malnutrition, prolonged negative nitrogen balance, diarrhoea and metabolic alkalosis. In Cushing's syndrome the excretion of potassium may also increase.
Increased serum sodium (hypernatraemia) occurs occasionally. The most common cause is rapid water loss, such as in diabetes insipidus. Hypernatraemia may also follow excessive sweating or result from either rapid administration of the sodium salts or hyperactivity of the adrenal cortex.
LOADING LOGS IN SRI LANKA to the heat, add malnutrition
Hyperkalaemia, or elevated levels of potassium, may occur in the case of renal failure, advanced dehydration or shock. It can also occur in Addison's disease. Muscular weakness and mental depression are generally observed, and the condition may be a hazard for the heart. Other symptoms commonly associated with hyperkalaemia include numbness and tingling of the extremities and ulceration of the small bowel.
Nutrition
Extensive research work on nutrition and physical performance has been done by many scientists and comprehensive analysis can be found in many standard textbooks. There are, however, some important new studies, according to which protein is not use as fuel to any appreciable extent when the caloric supply is adequate. It has been observed that during training periods athletes use only carbohydrate deposits for their energy requirements, provided their protein supply remains adequate. Thus, a carbohydrate-rich diet may be recommended for the person doing heavy exercise over an extended period in order to increase the glycogen level in muscles performing the heaviest work. Some authorities suggest that protein intake should not exceed 70-100 g g/day for workers performing strenuous labour. A nutrition-status survey carried out on forest workers in the Federal Republic of Germany shows a comparable average protein intake of 100-110 g/day.
Other research has shown that water and salt loss through sweating is the major factor that causes physical weakness and thus lowers the efficiency of long-duration work. Some recent studies suggest the need for water and salt supplementation in small amounts at frequent intervals during heavy physical performance.
A FOREST WORKER IN CENTRAL AMERICA his health ought to be more important than the wood he cuts
One of the primary mechanisms for regulating body temperature in hot climates is sweating. The rate of evaporation of sweat depends upon the humidity and air velocity. In the tropics, where high humidity and low air velocity usually go together the rate of sweat evaporation is decreased; this increases sweating and thus decreases work capacity. One researcher found that work capacity was reduced by 50 percent when the temperature rose from 25°C to 34°C at a wind velocity of 2 m/sec.
Under tropical conditions, a reduced caloric consumption is apparently a factor in maintaining satisfactory body temperature. It has been noted that the Tuareg nomads' diet is low in both calories and protein. No difference in the fitness and work performance of men exposed to varying climatic conditions in relation to dietary protein was found. It has also been shown that the total nitrogen loss of persons during 6½ hours' work in the heat was not affected by a high rate of sweating, and that therefore there is no evidence of the need for high-protein diets in hot climates.
It is well known that the mineral content of sweat depends upon the rate of sweating. An extremely high rate of sweating leads to dehydration. Under such a condition, the total electrolyte content of the body is decreased but the ionic concentration of extra-cellular sodium chloride tends to increase.
Studies of the effect of sodium chloride intake on work performance under heat stress showed no advantage of either high (30 g/day) or medium dosages (IS g/day) of salt. It appears that the doss of sodium and chloride ions by healthy men is significant only when caused by extended fasting, by heavy sweating or under a prolonged and severely salt-deficient diet. However, it has been claimed that men can also frequently develop a salt deficiency when subjected to severe heat stress or physical performance.
There is increasing evidence of potassium depletion from salt loading where salt tablets are given to military personnel and athletes in tropical countries. Military recruits and football players training in hot climates and gelling extra rations of salt are liable to suffer potassium depletion. It was found that daily losses of potassium in sweat and urine of heat-acclimatized subjects working in severe tropical heat can be about 116 mEq/day, compared to an intake of 97 mEq/day, thereby resulting in a negative balance of potassium.
Since many tropical countries are also poor countries, malnutrition is a very common problem. While a daily protein intake of 70-100 g protein may be sufficient for manual workers performing heavy work under heat stress, it must be recognized that some workers fail to get even this much protein in an often inadequate caloric intake.
Research results, however, do not allow a definite conclusion to be drawn regarding sodium chloride supplementation. The question of salt supplementation to workers is very important and needs immediate attention because overloading workers with salt tablets may cause a severe depletion of potassium. Responsible authorities in tropical countries should not underestimate the problem of potassium depletion among forest and manual workers, and they should recommend food rich in potassium and low in sodium to help prevent heat stroke and to avoid the danger of sodium overloading of body fluids.
