The relationship between physical activity, obesity, and lung cancer risk by smoking status in a large prospective cohort of US adults

Physical activity has been associated with lower lung cancer risk in numerous studies with estimates ranging from 20 to 50% lower risk in the most versus the least active study participants. Underweight and obesity have also been associated with lower lung cancer risk, with a nonlinear, inverted U-shaped relationship. However, associations of physical activity and obesity with lung cancer are likely significantly confounded by smoking since individuals who smoke are generally less active and leaner than non-smokers, but few studies have examined these associations stratified by smoking status. Using data from 162,679 men and women who were cancer-free at enrollment (1992–1993) in the American Cancer Society Cancer Prevention Study-II Nutrition Cohort, we examined associations of baseline recreational physical activity (MET-hours per week; none, 0.1 to