Supplementary Material for: The risk of depressive symptoms according to the dietary intake of vitamin C

Introduction: It has been hypothesized that vitamin C may have antidepressant effects through its antioxidant properties. However, evidence is still scarce to ascertain the effect of dietary vitamin C on depressive symptoms.
Methods: We conducted 5.9 years (median) follow-up on 91,113 Koreans who responded to the food frequency questionnaire and Center for Epidemiologic Studies Depression (CES-D) scale as items of the health check-up. They were categorized into four quartile groups based on dietary vitamin C intake and two groups based on the use of vitamin supplements. Incident depressive symptoms were determined by the identification of CES-D≥16 for follow-up. Cox proportional hazards model was used to calculate the multivariable-adjusted hazard ratio (HR) and 95% confidence intervals (CI) for depressive symptoms (multivariable adjusted HR [95% CI]) according to quartiles of dietary vitamin C intake. Subgroup analysis was conducted by sex and physical activity.
Results: In the analysis of all participants, there was no significant association between dietary vitamin C intake quartile groups and the risk of depressive symptoms (quartile 1: reference, quartile 2: 1.01 [0.96 - 1.06], quartile 3: 0.99 [0.93 – 1.05], and quartile 4: 1.00 [0.93 – 1.08]). No significant association was identically observed in both men and women. Vitamin supplementation was associated with the slight increase in the risk for depressive symptoms in all participants (1.08 [1.04 – 1.12]), men (1.06 [1.01 – 1.12]), and women (1.10 [1.04 – 1.16]).
Conclusion: An increase in dietary vitamin C intake and vitamin supplementation had no significant effect on reducing the risk of depressive symptoms.