Objectives
Metabolic syndrome is a global public health problem, and regular physical activity is a well-known critical factor in its management. A recent study suggests that the effect of exercise on metabolic syndrome may be enhanced by sufficient plasma vitamin C concentrations. We therefore examined the combined effect of physical activity and dietary vitamin C on the risk of metabolic syndrome in the general Korean population.

Study design
Cross-sectional study.

Methods
We analyzed data from 22,671 adults aged 20 years or older from the Korea National Health and Nutrition Examination Survey 2008–2012. Physical activity was computed as the total metabolic equivalent (METs-hr/week) summed from MET scores of walking, moderate activity, and vigorous activity. Vitamin C intake was assessed using a 24-h dietary recall. Participants were classified into four combined groups based on median values of physical activity and vitamin C intake.

Results
After adjustment for potential confounders, the odds ratio (OR) for metabolic syndrome in individuals with both high physical activity and vitamin C intake (vs. both low physical activity and vitamin C intake) was 0.79 (95% confidence interval (CI), 0.71–0.87). The estimated combined effect was more than either high physical activity alone (OR, 0.81 (95% CI, 0.73–0.90)) or high vitamin C intake alone (OR, 0.89 (95% CI, 0.80–0.99)), although each of those was beneficial.

Conclusions
Physical activity and dietary intake of vitamin C are both associated with a lower risk of metabolic syndrome. Our findings suggest further that a combination of physical activity and a diet rich in vitamin C may help in preventing metabolic syndrome.