the cold because of increased losses of respiratory water as well as losses induced by sweating. Cold conditions tend to reduce fluid intake because of logistical difficulties in supplying water and in preventing it from freezing. Water discipline is as important during cold stress as it is during heat stress.
The pair of problems created in meeting food and fluid needs is exaggerated when high-altitude stress is superimposed upon cold stress. Fluid needs become complicated by physiologic processes and hormonal effects that induce an antidiuretic effect in some individuals (see Anand and Chandrashekhar, Chapter 18 in this volume). This effect can contribute to AMS as well as to high-altitude pulmonary edema. More commonly, however, dehydration may become a potential military problem. Dehydration can result from several causes (see Cymerman, Chapter 16 in this volume), including reduced thirst, inadequate fluid intakes (from both water and foods), and increased sensible and insensible water losses associated with exercise. Again, water discipline is a military necessity.
Increased energy needs are also a separate but important issue at high altitudes. Weight loss is a common reality that must be met by increasing fuel intakes to meet additional energy needs (see Butterfield, Chapter 19 in this volume). Dehydration may also result in anorectic symptoms and lowered food intake. The provision of high calorie, energy dense snack-type foods was recommended by several participants in this workshop and by the CMNR in a previous report (IOM, 1995) as a potential means of providing extra food energy. Thus, the needs for supplying fluids and for supplying food must each be approached as equally important, and logistical support for cold and high-altitude work in the military must take into consideration the distinct differences in effort that are required for the adequate provision of each.
These issues can be summarized in two general questions:
1. Aside from increased energy demands, do cold or high-altitude environments elicit an increased demand or requirement for specific nutrients?
Cold and/or high-altitude environments can increase the needs for two important nutrients, water and carbohydrate (see answers to Questions 2, 5, 8, 10, and 15 in this chapter). Additional fat may sometimes be required to supply energy needs under certain circumstances (see reply to Question 4). While preliminary studies of increasing vitamin E intake to 400 mg/d show research promise in providing protective effects at high altitudes, considerable additional research is needed before questions regarding efficacy and effective doses are fully addressed and before implementing a supplement policy (see reply to Question 6). The needs for certain other single nutrients, i.e., vitamin C, iron, zinc, copper, and sodium, may also be increased (see comments on