Aging and human heat tolerance.

Collectively, the literature on heat tolerance suggests that middle-aged (45- to 64-year-old) men and women are more work-heat-intolerant and suffer more physiological strain during heat acclimation than younger individuals. However, it is unclear whether the age differences in work-heat intolerance and physiological strain during heat acclimation are related to age per se or associated with other factors such as certain disease states, decreased physical activity, or lowered aerobic fitness. In contrast, the work-heat tolerance and physiological responses during heat acclimation of habitually active or aerobically trained middle-aged men are the same as or better than younger individuals. The reviewed studies emphasize the importance of aerobic fitness and pertinent morphological factors, such as body fat, body weight, and surface area in maintaining work-heat tolerance with aging. Recent studies suggest that middle-aged and older men and women may be more susceptible to greater heat strain at physiologically significant levels of dehydration than those younger. However, additional research appears necessary to support this hypothesis. When the effects of chronic debilitating diseases in the elderly (64 years old and older) are minimized, their heat tolerance and thermoregulatory responses are comparable to those of younger individuals. In fact, healthy and well acclimated elderly men and women appear to perform as well as younger individuals during desert walks in dry heat. This review discusses experimental observations from previously published studies concerning aging and heat tolerance or the physiological heat strain during heat acclimation at rest or during work; and it suggests future research efforts needed to understand this topic better.