Exercise and immune function - Recent developments

Comparison of immune function in athletes and nonathletes reveals that the adaptive immune system is largely unaffected by athletic endeavour. The inn ate immune system appears to respond differentially to the chronic stress o f intensive exercise, with natural killer cell activity tending to be enhan ced while neutrophil function is suppressed. However, even when significant changes in the level and functional activity of immune parameters have bee n observed in athletes, investigators have had little success in linking th ese to a higher incidence of infection and illness. Many components of the immune system exhibit change after prolonged heavy e xertion. During this 'open window' of altered immunity (which may last betw een 3 and 72 hours, depending on the parameter measured), viruses and bacte ria may gain a foothold, increasing the risk of subclinical and clinical in fection. However, no serious attempt has been made by investigators to demo nstrate that athletes showing the most extreme post-exercise immunosuppress ion are those that contract an infection during the ensuing 1 to 2 weeks. T his link must be established before the 'open window' theory can be wholly accepted. The influence of nutritional supplements, primarily zinc, vitamin C, glutam ine and carbohydrate, on the acute immune response to prolonged exercise ha s been measured in endurance athletes. Vitamin C and glutamine have receive d much attention, but the data thus far are inconclusive. The most impressi ve results have been reported in the carbohydrate supplementation studies. Carbohydrate beverage ingestion has been associated with higher plasma gluc ose levels, an attenuated cortisol and growth hormone response, fewer pertu rbations in blood immune cell counts, lower granulocyte and monocyte phagoc ytosis and oxidative burst activity, and a diminished pro- and anti-inflamm atory cytokine response. It remains to be shown whether carbohydrate supple mentation diminishes the frequency of infections in the recovery period aft er strenuous exercise. Studies on the influence of moderate exercise training on host protection a nd immune function have shown that near-daily brisk walking compared with i nactivity reduced the number of sickness days by half over a 12- to 15-week period without change in resting immune function. Positive effects on immu nosurveillance and host protection that come with moderate exercise trainin g are probably related to a summation effect from acute positive changes th at occur during each exercise bout. No convincing data exist that moderate exercise training is linked with improved T helper cell counts in patients with HIV, or enhanced immunity in elderly participants.