Dietary iron is the most important source of iron stores. Several case-control studies have described the association of high dietary iron and Parkinson's disease, but prospective data are lacking. The authors prospectively followed 47,406 men and 76,947 women from the United States who provided information through a mailed questionnaire on their diet, medical history, and lifestyle practices between 1984 and 2000. The authors documented 422 new cases of Parkinson's disease. Total iron intake was not associated with an increased risk of Parkinson's disease (relative risk (RR) = 1.10, 95% confidence interval (CI): 0.74, 1.65; Ptrend = 0.84), but dietary nonheme iron intake from food was associated with a 30% increased risk of Parkinson's disease (RR = 1.27, 95% CI: 0.92, 1.76; Ptrend = 0.02). A secondary analysis revealed that Parkinson's disease risk was significantly increased among individuals with high nonheme iron and low vitamin C intakes (RR = 1.92, 95% CI: 1.14, 3.32; Ptrend = 0.002). Supplemental iron intake was associated with a borderline increase in Parkinson's disease risk among men. Although the authors' prospective data did not support an association between total iron intake (dietary and supplemental) and risk of Parkinson's disease, a 30% increased risk was associated with a diet rich in nonheme iron. This increase in risk was present in those who had low vitamin C intake.
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