executive session of the CMNR. Some areas of consideration were augmented by limited literature searches to ensure adequate coverage of each area.
Responses to Questions Posed by the Army
Below are the committee's answers to the five questions posed by the Army regarding nutrition and sustainment of immune function in the field.
1. What are the significant military hazards or operational settings most likely to compromise immune function in soldiers?
As described previously and outlined below, many conditions or stressors have been associated with compromised immune function during Ranger training and basic combat training, as well as during arctic training and in deployments to locations such as Somalia, Haiti, Panama, and the Persian Gulf.
Reduced ration consumption. Intakes less than 60 percent of the total energy needed, particularly during exposure to harsh environments and/or dehydration, were shown to be a significant stressor. In U.S. Ranger II, the increase in energy intake from that in Ranger I (2,780 to 3,250 calories or approximately 470 kcal/d), which tempered weight loss to only 12.8 percent of initial body weight, appeared to minimize the adverse effects on immune function. Thus, weight loss, particularly that involving lean body mass, appears to be a major factor in inducing immune system dysfunction.
The effects of dehydration on immune function are not reviewed in this report. However, weight losses of as little as 3–5 percent in 24–48 h, which are primarily due to dehydration, have a significant impact on performance. Weight losses of 6–10 percent in a similar period may affect health adversely. Thus, the effects of dehydration must be separated from those of underconsumption of rations (see IOM, 1995a).
- Prolonged moderate-to-heavy physical activity. The week-long Norwegian Ranger training studies with heavy exercise and limited sleep did not demonstrate significant weight loss or alterations in immune function, whereas the U.S. Ranger I study of 8- to 9-week duration demonstrated a greater weight loss (14 percent of body weight) and an altered immune response. Low- to moderate-intensity exercise (<60 percent Vo2 max), such as that performed in most troop activity of a duration of 60 minutes or less, appears to exert less stress on the immune system than activity that is more strenuous (>60 percent Vo2 max) performed for longer than 1 h. Repeated bouts of strenuous activity may increase the risk of infection, particularly of the upper respiratory tract.