Dietary glycemic index is inversely associated with the risk of Parkinson's disease: A case-control study in Japan

Objective: High glycemic index (GI) or glycemic load (GL) carbohydrates might be expected to decrease the risk of Parkinson's disease (PD) by an insulin-induced increase in brain dopamine. We conducted a hospital-based case-control study in Japan to examine associations between dietary GI and GL and other dietary carbohydrate variables, including intake of available carbohydrate and dietary fiber, and PD. Methods: Patients with PD diagnosed using the U.K. Parkinson's Disease Society Brain Bank criteria (n=249) and controls without neurodegenerative diseases (n=368) were recruited. Dietary intake during the preceding month was assessed at the time of study recruitment using a validated, self-administered, semiquantitative, comprehensive diet history questionnaire. Results: After adjustment for potential dietary and non-dietary confounding factors, dietary GI was significantly inversely associated with the risk of PD. Multivariate odds ratios (95% confidence intervals) for PD in the first, second, third, and fourth quartiles of dietary GI were 1.00 (reference), 1.03 (0.64-1.66), 0.68 (0.41-1.15), and 0.61 (0.34-1.09), respectively (P for trend=0.04). Conversely, no significant association was observed for other dietary carbohydrates, including dietary GL (P for trend=0.77), available carbohydrate intake (P for trend=0.28), or dietary fiber intake (P for trend=0.73). Conclusion: This preliminary case-control study based on current dietary habits found an independent inverse relation between dietary GI and PD. Considering the plausibility of the putative mechanism, further investigation using a case-control design with accurate assessment of past dietary habits or a prospective design is warranted.