Dietary Antioxidants and Risk of Parkinson's Disease: A Systematic Review and Dose–Response Meta-analysis of Observational Studies

The aim of the current review was to explore the association between various dietary antioxidants and the risk of developing Parkinson's disease (PD). PubMed, Scopus, Web of Science, and Google Scholar were searched up to March 2021. Prospective, observational cohort studies, nested case-control, and case-control designs that investigated the association between antioxidants and PD risk were included. A random-effects model was used to pool the relative risks (RR). The certainty of the evidence was rated using the GRADE scoring system. In addition, a dose-response relationship was examined between antioxidant intake and PD risk. Six prospective cohort studies and two nested case-control (total n = 448,737 with 4654 cases), as well as six case-control studies (1948 controls, 1273 cases) were eligible. The pooled RR was significantly lower for the highest compared to the lowest intake categories of vitamin E (0.84, 95% CI 0.71, 0.99, n = 7), and anthocyanins (0.76, 95% CI: 0.61, 0.96, n = 2) in cohort studies. Conversely, a significantly higher risk of PD was observed for higher lutein intake (1.86, 95% CI: 1.20, 2.88, n = 3) among case-control studies. Dose-response meta-analyses indicated a significant association between a 50 mg/d increase in vitamin C (RR: 0.94, 95% CI: 0.88, 0.99, n = 6), a 5 mg/d increment in vitamin E (RR: 0.84, 95% CI: 0.70, 0.99, n = 7), a 2 mg/d increment in β-Carotene (RR: 0.94, 95% CI: 0.89, 0.99, n = 6), and a 1 mg/d increment in zinc (OR: 0.65, 95% CI: 0.49, 0.86; n = 1) and the reduced risk of PD. Overall, higher intake of antioxidant-rich foods may be associated with a lower risk of PD. Future, well-designed prospective studies are needed to validate the present findings.