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under these conditions. However, no clear evidence indicates whether zinc in excess of the MRDAs should be recommended. Once again, caution is required in considering supplementation: zinc supplements reportedly lower the absorption of copper, a nutrient that already may be marginal in many diets (NRC, 1989b).

Magnesium and Copper

Sweat losses of magnesium and copper, like those of other trace elements, can be appreciable. Negative nitrogen, potassium, and magnesium balances were produced in young men by diminished dietary intake, increased urinary excretion, and sweat losses during hyperthermia induced by humid heat in an experimental chamber (Beisel et al., 1968). In some studies involving intense exercise the plasma levels of these elements have increased and in other studies they decreased. It should be noted however, that plasma levels of both elements are not a useful measure of body stores.

Calcium and Phosphorus

Calcium and phosphorus were not addressed specifically at the workshop. Based on current knowledge, the existing MRDAs for these nutrients appear to be sufficient for nutritional needs even during profuse sweating in a hot environment.

Summary

It is unclear whether mineral losses resulting from chronic heat exposure or exercise, or both, result in compromised health and performance (endurance capacity, immune defense, antioxidant defense, or recovery from illness or trauma). This information is essential before the applicability of the MRDAs can be fully assessed for military personnel working in hot environments.

FACTORS THAT MAY INFLUENCE EATING PATTERNS, FOOD PREFERENCES, AND FOOD INTAKE IN HOT ENVIRONMENTS

Olfaction and Taste

Chapter 9 reviews flavor effects (taste-gustation, smell-olfaction) and trigeminal sensation including touch, temperature, and pain, as well as color and psychological factors that affect sensory aspects of food consumption. Subject variables (age, gender, ethnic group, disease state, etc.) were not explored.



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