The Mediating Effect of Vitamin D on the Association Between Exercise and Triglyceride in Adolescents: A Prospective Cross-sectional Study

ObjectiveTo investigate the mediating role of vitamin D in the association between exerciseand triglyceride among adolescents, as well as its potential molecular mechanisms.MethodsThis prospective cross-sectional study utilized convenience sampling, enrolling 2021-grade students from Jining No. 7 Middle School on June 5, 2023. Moderate-intensity exercise frequency was assessed via standardized questionnaires, serum 25-hydroxyvitamin D levels were measured using chemiluminescence, and triglyceride levels were determined via fully automated biochemical analysis. Spearman's rank correlation analysis was employed to examine the relationships among moderate-intensity exercise, triglyceride, and vitamin D. A mediation model was constructed using the Baron & Kenny causal steps approach, adjusting for confounders including age, sex, body mass index (BMI), dairy intake, sweet food consumption, and fast-food intake. Subgroup analyses were performed based on BMI. The significance of the mediation effect was confirmed using both the Bootstrap and Sobel tests.ResultsA total of 354 adolescents meeting the inclusion criteria were enrolled, including 142 females (40.11%) and 212 males (59.89%), with a median age of 13.25(12.83, 13.83)years. Spearman's analysis revealed a significant negative correlation between moderate-intensity exercise and triglyceride levels (r=-0.21, P < 0.001), a significant negative correlation between vitamin D and triglyceride (r=-0.30, P < 0.001), and a significant positive correlation between moderate-intensity exercise and vitamin D levels (r=0.26, P < 0.001). The mediation model indicated that vitamin D partially mediated the triglyceride-lowering effect of exercise (52.22%, 95% CI: -0.027 to -0.009, P < 0.001), with the effect remaining significant after confounder adjustment (47.83%, 95% CI: -0.019 to -0.005). Subgroup analysis showed that in adolescents with BMI < 24 kg/m2, vitamin D accounted for 82.01% of the mediation effect between exercise and triglyceride (95% CI: -0.022 to -0.005, P=0.005), which remained significant after adjustment (81.20%, 95% CI: -0.022 to -0.005, P=0.005). In contrast, among adolescents with BMI ≥24 kg/m2, the mediation effect was nonsignificant before (3.38%, 95% CI: -0.014 to 0.009, P=0.760) and after adjustment (7.51%, 95% CI: -0.019 to 0.012, P=0.621).ConclusionsVitamin D serves as a key mediator in the triglyceride-lowering effect of exercise among adolescents, independent of age, sex, and dietary habits. This mediation effect is particularly pronounced in adolescents with BMI < 24 kg/m2. The underlying mechanism may involve vitamin D-regulated lipid metabolism-related gene expression and suppression of inflammatory pathways, suggesting that targeting vitamin D signaling could be a potential molecular strategy for early intervention in adolescent dyslipidemia.