Heterogeneity in the Protective Effect of Physical Activity on Type 2 Diabetes: Differential Modifying Effects of Obesity and Age on the Dose-Response Relationship

BackgroundIndividuals with severe mental disorders represent a very high-risk population for diabetes and its complications. Physical inactivity and sedentary behavior are shared behavioral risk factors for type 2 diabetes (T2DM) comorbidity. However, whether the protective effect of physical activity (PA) on T2DM is modified by obesity and age, and its specific dose-response relationship, remain unclear. MethodsThis study utilized cross-sectional data from 5,042 adults in the 2017-2020 National Health and Nutrition Examination Survey (NHANES). Weighted multivariable logistic regression and restricted cubic splines (RCS) models were employed to analyze the association between PA and T2DM risk and to assess the potential effect modification by BMI and age. ResultsAfter adjusting for confounders, higher levels of PA were independently associated with a lower risk of diabetes. Dose-response analysis using RCS revealed significant effect modification: the protective effect of PA exhibited a distinct "BMI gradient," being strongest in normal-weight individuals, attenuated in those with overweight, and absent in those with obesity. Concurrently, an "age stratification" was observed, with the protective effect being strongest in middle-aged adults, showing a borderline significant trend in young adults, and demonstrating no significant association in older adults. ConclusionThis study confirms that the protective effect of PA against T2DM is jointly modified by obesity and age. Future prevention strategies should shift from universal recommendations towards precise, stratified guidance based on BMI and age, which holds significant implications for the integrated care of individuals with mental disorders.