Immune responses to exercising in a cold environment.

Cold temperature and exercise independently impose stress on the human body that can lead to circulatory and metabolic changes, and depress the immune system. Multiple stressors applied together may amplify this immunodepression, causing greater immune impairment and heightened infection risk than with either stressor alone. As such, winter athletes and other persons who work or physically exert themselves in cold temperatures may have greater levels of stress-induced immune impairment than would be expected under mild temperatures. This review examines the literature regarding changes to physiological and immunological parameters arising from exposure to cold temperatures and to exercise. Even brief exposure to cold leads to increased levels of norepinephrine and cortisol, lymphocytosis, decreased lymphoproliferative responses, decreased levels of TH1 cytokines and salivary IgA, and increased lactate levels during exercise. Whether these changes lead to increased susceptibility to infection, as suggested by some epidemiological reports, remains to be determined. Although there is some evidence that exercising in temperatures near 5°C leads to greater immune impairment compared to exercising in milder temperatures, there is a need to explore the effects of exercise on immunity in the subfreezing conditions typically encountered by winter athletes. This is required to fully determine the extent to which performing vigorous exercise in subfreezing temperatures amplifies exercise-induced immune impairment and infection risk.