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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations
stances in which the performance of military personnel would be improved by the use of electrolyte-carbohydrate beverages (see Marriott and Rosemont, 1991). In these cases, such beverages should provide approximately 20 to 30 milliequivalents (mEq) of sodium and 2 to 5 mEq of potassium per liter, with chloride as the only anion.
Iodide, Chromium, and Selenium
Sweat losses of iodide, chromium, and selenium are appreciable with intense exercise or in a hot environment. In the case of iodide, the losses that occur during profuse sweating make the use of iodized salt highly desirable. With intense exercise, plasma chromium increases, urinary chromium decreases, and plasma selenium decreases. As discussed above, the significance of these changes for the mineral status of an individual is not clear.
Iron deficiency can reduce physical performance; it has also been reported to result in a defect in thermoregulation. Losses of iron during heavy sweating can be considerable. Although anemia (i.e., "sports anemia") may occur during training, it is transitory and due in part to plasma volume expansion. Iron deficiency anemia is not commonly seen with chronic intense exercise, although low serum ferritin levels have been observed. Low serum ferritin levels are an indication that iron stores are not high and that an acute loss of iron or a decrease in intake will almost certainly result in anemia. However, caution must be employed when using iron supplements because of their reported adverse effect on zinc absorption and the potential for creating iron overload in some individuals if used for a prolonged period.
Sweat losses of zinc can present a significant problem for military personnel in a hot environment, whether they are exercising or not. Intense exercise has been observed in some instances to increase, and in others to decrease, plasma zinc concentrations. The low plasma zinc values could also result from an acute metallothionein-induced sequestration of zinc within hepatic cells. Such interleukin-1 (IL-1) generated zinc redistribution occurs during many stress situations, and does not cause loss of zinc from the body. The frequent observation of lowered plasma zinc levels during chronic and prolonged exercise, when considered together with the high sweat losses that have been observed, suggests the appropriateness of zinc supplements