Sex-specific associations of physical activity and sedentary time with obesity: a longitudinal study in China

Moderate to vigorous physical activity (MVPA) and sedentary time (ST) have been associated with obesity, but their sex-specific associations with body mass index (BMI) and abdominal obesity remain underexplored. This study examined these associations in Chinese adults. This retrospective cohort study, conducted from 2014 to 2020, included 43,429 participants from a Chinese health management center. Data were collected from anthropometric measurements and online questionnaire surveys. Generalized estimating equations (GEE) models were used to examine the associations and to test sex interactions. In the fully adjusted model, longer ST was associated with higher odds of both BMI (e.g., > 6 h/day: OR = 1.071, 95% CI: 1.016–1.130) and abdominal obesity (e.g., > 6 h/day: OR = 1.125, 95% CI: 1.074–1.178), whereas qualified MVPA was associated with lower odds of both BMI (OR = 0.893, 95% CI: 0.860–0.927) and abdominal obesity (OR = 0.887, 95% CI: 0.860–0.914). Significant sex interactions were observed for MVPA with both outcomes ( p = 0.002 for BMI; p < 0.001 for abdominal obesity) and for ST with abdominal obesity ( p = 0.003), but not for ST with BMI ( p = 0.161). Sex-stratified analyses revealed a stronger inverse association between MVPA and abdominal obesity in males (OR = 0.874, 95% CI: 0.845–0.904) than in females (OR = 0.924, 95% CI: 0.863–0.991). For ST and BMI, the formal interaction was not significant, and the observed sex-stratified difference should be interpreted as exploratory. These findings suggest that sex-specific patterns may exist in the associations between MVPA, ST, and obesity. Further research is needed to inform sex-tailored public health strategies.