However, there is insufficient evidence at this time to recommend an increase in vitamin C beyond that currently supplied by the MRDA.

Prolonged moderate-to high-intensity activity in hot environments will result in a significant loss of electrolytes (sodium, potassium, magnesium), particularly among troops who are not adapted to hot environments. However, if fluid intake is maintained to prevent dehydration and consumption of military rations is at or near energy requirements, sufficient intake of electrolytes should occur.

10. Does working in a hot climate change an individual's absorptive or digestive capability?

There is evidence that gastric emptying may be reduced during heat stress. Although the mechanisms responsible for this observation are unclear, they may be associated with dehydration, which frequently occurs when working in the heat, and with reduced splanchnic blood flow. Studies have also demonstrated that elevations in core body temperature can reduce stomach and intestinal motility. It is apparent that maintaining adequate fluid intake is important as an aid in reducing heat stress from working in a hot environment.

Limited evidence suggests that net calcium absorption may be reduced as a result of increased fecal losses during profuse sweating while working in hot environments. Some investigators have reported reduced intestinal absorption during exercise. However, other studies, by using more direct techniques of segmental perfusion, have shown no effect of either exercise intensity or duration on fluid absorption. In short, individuals who are well trained, acclimatized to heat, and accustomed to endurance exercise seem to experience fewer symptoms of gastrointestinal stress than less well conditioned and acclimatized individuals.

11. Does work at a moderate to heavy rate increase energy requirements in a hot environment to a greater extent than similar work in a temperate environment?

Uncertainty exists about the influence on energy requirements of working in the heat (see Chapter 6). Submaximal exercise in a hot environment does not appear to have an impact greater than that occurring in a more comfortable environment. Maintaining adequate food intake in the temperature extremes of hot environments to meet caloric needs is a higher priority than concern over small differences in energy requirements.

On the basis of the papers presented by the invited speakers, discussion at the workshop, and subsequent committee deliberations, the Committee on