The effect of vitamin C supplementation on mood status in adults : a systematic review and meta-analysis of randomized controlled clinical trials

Objective: We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) to clarify the effect of vitamin C supplementation on mood in both depressed and non-depressed populations. Methods: A systematic search of PubMed, EMBASE, ISI web of science and Scopus databases was conducted, from inception to 1 March 2020. Random-effects meta-analyses were used to estimate the effect size (as Hedge's g) of vitamin C supplementation on depressive symptoms. Results: Finding from 10 trials with 836 participants revealed no significant improvement in mood status in overall analysis (n = 10, Hedge's g = 0.09; 95% confidence interval: −0.15 to 0.33; P = 0.465). However, subgroup analysis showed beneficial effects of vitamin C supplementation in patients who were not prescribed antidepressants (subclinical depressed) (n = 5, Hedge's g: −0.18; 95% CI: −0.35, −0.01, P = 0.041; I² = 0.00%,). Conclusions: Although no significant effect on mood status was observed in overall population, this meta-analysis tentatively suggests that vitamin C may produce mood-elevating effects in patients with subclinical depression. Further research is recommended to reach a firm conclusion. Protocol registration: The study protocol was registered in the international prospective register of systematic reviews database (http://www.crd.york.ac.uk/PROSPERO, registration no: CRD42018086677).