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

Abstract 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.