Joint association of physical activity and body weight with subsequent physical and mental functioning: a follow-up study

BACKGROUND Physical inactivity and overweight are major threats to public health. However, it is not well understood to what extent physical activity might counteract the harmful effects of overweight on functioning. Thus, we examined the joint associations of leisure-time physical activity and body mass index (BMI) with subsequent physical and mental functioning over a follow-up of five to seven years. METHODS The data were derived from the Helsinki Health Study, which is a cohort study among employees of the City of Helsinki, Finland. The baseline postal survey data were collected among 40-60-year-old employees in 2000-02 (n = 8960, response rate 67%), and the follow-up data in 2007 among all baseline survey respondents (n = 7332, response rate 83%). We divided the participants into six groups according to their amount of physical activity (inactive, moderately active and highly active) and their relative weight (normal weight and overweight). Highly active normal-weight participants were used as a reference group in all the analyses. Poor functioning was defined as the lowest quartile of the Short Form 36 (SF-36) health survey's physical and mental component summaries, with the follow-up cut-off point also applied at baseline. We used logistic regression analysis adjusted for age, gender, baseline functioning, smoking, alcohol use, marital status, socioeconomic position and working conditions. RESULTS At baseline 48% of the participants were overweight and 11% were inactive. After adjustments inactivity was associated with poor physical functioning at follow-up both among the normal-weight (OR 1.51, 95% CI 1.09-2.10) and overweight (OR 2.02, 95% CI 1.56-2.63) groups. Being overweight regardless of activity level was associated with poor physical functioning. Poor physical functioning was practically equally common among the highly active overweight group and the inactive normal-weight group. After adjustments, for mental functioning, only inactivity among the overweight was associated with poor mental functioning (OR 1.39, 95% CI 1.08-1.80). CONCLUSIONS Physical activity is likely to be beneficial for physical and mental functioning among both those with overweight and normal weight. However, maintaining normal weight is also important for good physical functioning. Therefore, efforts should be made to recommend people to engage in physical activity regardless of weight.