It has been proposed that moderate exercise may enhance the immune system. We evaluated whether physical activity at work or at leisure is associated with the risk of
pneumonia, and whether the
antioxidants vitamin E and
beta-carotene affect
pneumonia risk in physically active people. A cohort of 16 804 male smokers aged 50-69 years and working at study entry was drawn from the
Alpha-Tocopherol,
Beta-Carotene Cancer Prevention (ATBC) Study, which examined the effect of
vitamin E, 50 mg/day, and
beta-carotene, 20 mg/day, on lung and other
cancers. Physical activity at work, and the type of leisure-time exercise, were recorded at study entry. We retrieved the first occurrence of hospital-treated
pneumonia during a 3-year follow-up from the National Hospital Discharge Register (133 cases). Physical activity at work and at leisure had no association with the risk of
pneumonia. In participants with physically loading jobs, neither
vitamin E nor
beta-carotene affected the risk of
pneumonia. In participants carrying out moderate or heavy exercise at leisure,
beta-carotene had no effect, but
vitamin E reduced the risk of
pneumonia by 50% (95% CI: 16-70%). Previously, exercise has been shown to affect diverse laboratory measures of the immune system which are, however, only
surrogate markers for the resistance to
infections. The lack of association between physical activity and the risk of
pneumonia observed in our study emphasizes the problem of drawing conclusions from
surrogate end points. The finding that
vitamin E reduced the risk of
pneumonia in persons carrying out leisure-time exercise warrants further study.