Sports participation and obesity incidence in chinese adolescents: a 7-year prospective cohort study.

Adolescent obesity has risen to become a critical public health challenge around the world. According to the World Health Organization, roughly 340 million children and adolescents aged 5-19 were overweight or obese by 2016, representing a nearly sixfold increase since 1975. In China, rapid urbanization and shifting dietary patterns have accelerated this trend among school-age populations. Although physical activity is broadly considered protective against weight gain, longitudinal evidence that quantifies the magnitude of sports participation's effect on obesity incidence during adolescence remains sparse. We aimed to examine the dose-response relationship between sports participation intensity and seven-year obesity incidence among Chinese adolescents, and to identify subgroup-specific effect modification by sex, age, and baseline body mass index. We conducted a prospective cohort study drawing on data from the National Adolescent Health Surveillance System. A total of 89,532 initially non-obese Chinese adolescents aged 12-15 years were followed from 2016 to 2023. Sports participation intensity was assessed biannually through validated questionnaires, and obesity incidence was ascertained using WHO age- and sex-specific BMI criteria. Cox proportional hazards regression models were fitted with adjustment for demographic, socioeconomic, and time-varying behavioral confounders. Propensity score matching and marginal structural models served as supplementary analytical approaches to strengthen causal inference. Over 523,847 person-years of observation, 8,947 incident obesity cases were identified (17.1 per 1,000 person-years). Compared with minimal physical activity, high sports participation (≥ 300 min/week) was associated with a 58% lower obesity risk (HR = 0.42, 95% CI 0.37-0.48), and a clear dose-response gradient was observed. Moderate and low participation showed intermediate protective effects (HR = 0.61 and 0.73, respectively). These associations held up across multiple sensitivity analyses and were stronger among boys than girls. Sustained sports participation during adolescence substantially reduces obesity incidence in a dose-dependent manner. These findings offer compelling support for physical activity promotion policies and school-based interventions targeting this critical developmental period. This study was reported following the STROBE guidelines for observational studies.