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; I = 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).