Physical activity in relation to all-site and lung cancer incidence and mortality in a sample of current and former smokers

Physical activity has been shown to have a protective effect on risk and mortality from all-site cancer and some site-specific cancers in primarily non-smoking samples; however, little is known about whether physical activity affords similar reductions in risk and mortality among smokers. Additionally, neither the optimal frequency, duration, or intensity of activity that is most protective against cancer are known, nor is it known when in the lifespan physical activity is most beneficial. This study examined physical activity in relation to all-site cancer and lung cancer incidence and mortality in a sample (n = 7,733) drawn from the CARET study, a 13-year chemoprevention trial with a population of current and former smokers. Cox regression analyses revealed that physical activity was protective in a predominately dose-response fashion against all-site and lung cancer incidence and mortality in the early years of follow-up but not in the later years. Few cancer risk factors confounded or mediated these associations, and the results did not differ by the level of past smoking. Additional analyses suggested that adding hours of physical activity at any intensity conferred additional protection, but adding vigorous activity may be most protective. No particular pattern of life span physical activity was more important than another. These results suggest that physical activity may be an important factor in cancer prevention even among heavy smokers.