Longitudinal transitions in sedentary behavior and physical activity in relation to all-cause and cause-specific mortality among postmenopausal women

To evaluate longitudinal transitions in sedentary behavior and physical activity for the associations with all-cause and cause-specific mortality (i.e., cardiovascular disease [CVD], cancer, respiratory, and Alzheimer's disease/dementia mortality) among postmenopausal women. This prospective cohort study included 58,168 multiethnic US postmenopausal women from the Women’s Health Initiative Observational Study, who had self-reported data on various sedentary behaviors and recreational physical activity at baseline (Y0: 1993–1998; age range: 50–79 years) and after 6 years (Y6). According to sedentary time (≥ 8 h/day or not) or physical activity (≥ 8.5 MET-h/week or not) at Y0 and Y6 assessments, participants were grouped by transition in sedentary behavior (consistently non-sedentary, sedentary to non-sedentary, non-sedentary to sedentary, and consistently sedentary) or physical activity levels (consistently low, high to low, low to high, and consistently high). Over a median follow-up of 15.0 years (from Y6 to March 2019), 17,354 all-cause deaths occurred, ranging from 1336 respiratory to 5111 CVD deaths. Compared to the consistently non-sedentary group, the two groups with unfavorable transitions in sedentary behavior (i.e., from non-sedentary to sedentary or being consistently sedentary) both had a higher risk of all-cause mortality and mortality from CVD, cancer, and respiratory disease. Conversely, the two groups with favorable transitions in physical activity (i.e., transitioning to or maintaining high activity), as compared with the consistently-low activity group, both had a lower risk mortality from all causes and several specific causes. Significant interactions were observed between transitions in sedentary behavior and physical activity on the risk of all-cause and CVD mortality (P-interaction < 0.01). Specifically, unfavorable sedentary transitions were associated with an elevated risk only among women with unfavorable transitions in physical activity. Among US postmenopausal women, maintaining or transiting to a sedentary lifestyle over 6 years was associated with a higher risk of mortality, predominantly among those not achieving regular physical activity over the years.