Effect of dietary vitamins C and E on the risk of Parkinson's disease: A meta-analysis

Background & aims: A neuroprotective effect of dietary vitamins C and E on Parkinson's disease (PD) has been suggested, however, several human studies have reported controversial results. Therefore, we conducted a meta-analysis on the effect of vitamins C and E on the risk of Parkinson's disease. Methods: A comprehensive literature search was conducted using the PubMed, EMBASE, Cochrane Library, and SCOPUS databases for studies published up to January 23, 2021. We included studies that reported (1) intake of vitamins C and E using validated methods; (2) assessment of odds ratio (OR), relative risk (RR), or hazard ratio (HR); and (3) patients with PD identified by a neurologist, hospital records, or death certificates. The Comprehensive Meta-Analysis Software 2 program was used for statistical analyses of the pooled data. Results: A total of 12 studies (four prospective cohort and eight case-control studies) were included in our meta-analysis. No significant risk reduction was observed in the high vitamin C intake group compared to low intake group. On the other hand, the high vitamin E intake group showed a significantly lower risk of development of PD than the low intake group (pooled OR = 0.799. 95% CI = 0.721 to 0.885). Conclusions: We conclude that vitamin E might have a protective effect against PD, while vitamin C does not seem to have such an effect. However, the exact mechanism of the transport and regulation of vitamin E in the CNS remains elusive, and further studies would be necessary in this field. (c) 2021 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.