The Combined Impact of Environment Heat Stress and Exercise on Immune Function

Abstract

Background: The impact of heat stress alone on immune function is complex in nature; however, it appears a core temperature within the range of 37–39±C has little impact on neutrophil, lymphocyte and natural killer cell function. However, during passive heating where core temperature increases outside of this range there is a proliferation in leukocytes and cytokines with the magnitude dependent upon the extent and the duration of the heat stress. Laboratory and field-based experiments investigating the effect of exercise on immune function have shown moderate levels of training enhances the immune function; however, both high intensity acute and chronic exercise can result in immune suppression. Research has shown that immune suppression is at least partly responsible for the reported increase incidence of infection in athletes, which is influenced by a number of factors including, and possibly a combination of intensity and duration of exercise; and the psychological stress of training and competition. Given that both passive heating and exercise can have significant effects on the immune function that are based upon the stress experienced, it seems plausible that combined impact of heat stress and exercise stress may have an accumulative effect. Conclusion: Unfortunately, relatively little is known about the immunosuppressive effect of exercising in extreme temperature. This is an important consideration to individuals completing physical labour or athletes training and playing in an extreme environment such as that experienced during the summer months in Qatar.