Interaction Between Vitamin D Status and Aerobic Physical Activity in Relation to Cardiometabolic Risk Clustering Among Rural Older Adults

Background/Objectives: This study investigated whether serum 25-hydroxyvitamin D (25(OH)D) modifies the association between meeting WHO aerobic physical activity guidelines and cardiometabolic risk clustering among rural older adults in South Korea. Methods: This cross-sectional study analyzed 2023 Korea National Health and Nutrition Examination Survey (KNHANES) data for rural-dwelling adults aged ≥65 years with complete data (n = 441). Cardiometabolic risk clustering (CMRC) was defined as the presence of ≥3 of five risk factors (abdominal obesity, elevated blood pressure, low HDL-cholesterol, elevated triglycerides, and hyperglycemia). Exposures were continuous serum 25-hydroxyvitamin D (25(OH)D) and adherence to the WHO aerobic physical activity guidelines (yes/no). Multivariable logistic regression models tested the 25(OH)D × physical activity interaction, adjusting for sex, age (≥75 vs. <75 years), education, household income, smoking status, alcohol use, and obesity (BMI ≥ 25 kg/m2). Conditional effects of physical activity were estimated at the 16th, 50th, and 84th percentiles of 25(OH)D. Results: A significant interaction between 25(OH)D and physical activity was observed (OR = 0.91, 95% CI: 0.85–0.97; p = 0.005). Physical activity was not associated with CMRC at low 25(OH)D (16th percentile, 17.08 ng/mL; OR = 1.64, 95% CI: 0.78–3.47), but it was associated with lower odds of CMRC at high 25(OH)D (84th percentile, 36.98 ng/mL; OR = 0.25, 95% CI: 0.10–0.62). Conclusions: Vitamin D status modified the association between aerobic physical activity and cardiometabolic risk clustering among rural older adults. Integrated prevention strategies addressing both physical activity and vitamin D insufficiency may be valuable in rural aging populations.