AIMS Continuing physical activity (PA) and maintaining body weight are tightly intertwined; however, no study investigated whether these two factors have interactions in terms of the mortality. The aim of this study is to elucidate whether continuing regular PA and maintaining body weight have interactions in terms of all-cause mortality risk.

METHODS AND RESULTS Participants with health screening from both 2009 and 2011 without underlying cancer or cardiovascular disease were included. Physical activity change was grouped as remained active, inactive-to-active, active-to-inactive, or remained inactive. Body weight change was categorized as stable (weight change < 5%), weight gain, or loss. Outcome included all-cause mortality. Of 6 572 984 total participants, 91 347 deaths occurred during a median 7.4-year follow-up. Compared with the remained active and stable weight group, most other groups had a higher mortality risk. The weight loss and remained inactive group [adjusted hazard ratio (aHR), 2.30; 95% confidence interval (CI), 2.22-2.38] and the weight gain and remained inactive group (aHR, 2.17; 95% CI, 2.09-2.25) showed the highest mortality risks. Among stable weight participants, the ranking of the groups from highest to lowest in terms of mortality risk was as follows: remained inactive (aHR, 1.46; 95% CI, 1.41-1.50), active-to-inactive (aHR, 1.24; 95% CI, 1.19-1.29), inactive-to-active (aHR, 1.15; 95% CI, 1.11-1.20), and remained active (reference). Remaining active and maintaining a stable body weight had a synergistic interaction on decreasing all-cause mortality risk (multiplicative P for interaction < 0.001; relative excess risk due to interaction, 0.38; 95% CI, 0.31-0.46; attributable proportion, 0.18; 95% CI, 0.15-0.22).

CONCLUSIONS Continuing regular PA as recommended and maintaining body weight have multiplicative and additive interactions on reducing all-cause mortality. Healthcare providers should emphasize the importance of both regular PA and body weight maintenance for the general public.