Smoking and body mass in the natural history of physical activity: prospective evidence from the Alameda County Study, 1965-1974.

The prospective effects of smoking status and body mass on change in leisure-time physical activity from 1965 to 1974 were examined in a cohort of 4,622 persons 20-94 years of age from the Alameda County Study. With adjustment for age and baseline physical activity, current smokers showed a greater nine-year decline in leisure-time physical activity than those who had never smoked. The coefficient for current smokers from a multivariate linear regression model was of a similar magnitude among women and men (coefficient = -0.27, 95% confidence interval [CI] = -0.50 to -0.05 for women; coefficient = -0.26, 95% CI = -0.54 to 0.02 for men). Larger declines in physical activity were seen with increasing number of current pack-years exposure among both women and men. Compared with women of average body mass index, women of heaviest body mass index had larger declines (coefficient = -0.70, 95% CI = -1.04 to -0.36) while women of the lightest body mass index had larger increases (or smaller declines) in physical activity (coefficient = 0.33, 95% CI = 0.00 to 0.66). Although body mass index did not initially appear to be associated with a change in physical activity among men, age-specific analyses indicated that the effect of body mass index on physical activity varied with age such that younger (20-39 years of age), thinner men increased their activity, while older (60 years of age and over), thinner men decreased their physical activity more than men of the same age with average body mass index.