Dietary intake of iron, zinc, copper, and risk of Parkinson's disease: a meta-analysis.

Although some studies have reported the associations between specific metal element intake and risk of Parkinson's disease (PD), the associations between specific metal element intake such as iron intake and PD are still conflicted. We aimed to determine whether intake of iron, zinc, and copper increases/decreases the risk of PD. PubMed, Embase, Web of Knowledge, and Google Scholar were searched. We pooled the multivariate-adjusted relative risks (RRs) or odds ratios using random effects. Study quality was evaluated by the Newcastle-Ottawa Scale. Five studies including 126,507 individuals remained for inclusion, pooled RRs of Parkinson's disease for moderate dietary iron intake was 1.08 (95 % CI 0.61-1.93, P = 0.787), and for high dietary iron intake was (1.03, 95 % CI 0.83-1.30, P = 0.766), respectively. The pooled RRs of Parkinson's disease for the highest compared with the lowest dietary iron intake were 1.47 (95 % CI 1.17-1.85, P = 0.001) in western population and in males (RR = 1.43, 95 % CI 1.01-2.01, P = 0.041). The pooled RRs of Parkinson's disease for moderate or high intake of zinc, and copper were not statistically different (P > 0.05). PD increased by 18 % (RR 1.18, 95 % CI 1.02-1.37) for western population by every 10-mg/day increment in iron intake. Higher iron intake appears to be not associated with overall PD risk, but may be associated with risk of PD in western population. Sex may be a factor influencing PD risk for higher iron intake. However, further studies are still needed to confirm the sex-selective effects.