Joint Association of Sedentary Time and Physical Activity with Metabolic Syndrome Among Korean Adults: A Cross-Sectional Analysis of the 2024 Korea National Health and Nutrition Examination Survey

Background/Objectives: This study examined the joint association of sedentary time and physical activity with metabolic syndrome among Korean adults and whether physical activity modified this association. Methods: This cross-sectional study analyzed 2024 Korea National Health and Nutrition Examination Survey data from 3075 adults aged ≥19 years. Participants were classified into four groups by sedentary time and physical activity recommendation status. Complex-sample logistic regression was performed, with additional analyses of independent associations, interactions, and sensitivity analyses. Results: Compared with the low sedentary time/meeting group, the high sedentary time/not meeting group had higher odds of metabolic syndrome after adjustment for sociodemographic and health-related factors (OR = 1.38, 95% CI: 1.07–1.78; p = 0.013). No significant multiplicative interaction was observed (interaction OR = 1.08, 95% CI: 0.74–1.57; p = 0.681), and additive interaction indices were also nonsignificant. Each additional hour/day of sedentary time was associated with 4% higher odds of metabolic syndrome (OR = 1.04, 95% CI: 1.01–1.07; p = 0.011). After additional BMI adjustment, the association for the high sedentary time/not meeting group was not statistically significant (OR = 1.34, 95% CI: 0.98–1.83; p = 0.065). Conclusions: High sedentary time combined with not meeting the physical activity recommendation was associated with higher odds of metabolic syndrome. However, no significant multiplicative or additive interaction was identified. These findings support joint consideration of sedentary time and physical activity without implying that physical activity offsets the association of prolonged sedentary time with metabolic syndrome.