Body Mass Index and Risk of Parkinson's Disease: A Dose-Response Meta-Analysis of Prospective Studies

Background A number of epidemiologic studies examining the relationship between body mass index (BMI) and the future occurrence of Parkinson's disease (PD) reported largely inconsistent findings. We conducted a dose-response meta-analysis of prospective studies to clarify this association. Methods Eligible prospective studies were identified by a search of PubMed and by checking the references of related publications. The generalized least squares trend estimation was employed to compute study-specific relative risks (RR) and 95% confidence intervals (CI) for an increase in BMI of 5 kg/m(2), and the random-effects model was used to compute summary RR and 95% CI. Results A total of 10 prospective studies were included in the final analysis. An increase in BMI of 5 kg/m(2) was not associated with PD risk, with a summary RR of 1.00 (95% CI = 0.89-1.12). Results of subgroup analysis found similar results except for a week positive association in studies that adjusted for alcohol consumption (RR = 1.13, 95% CI = 0.99-1.29), and a week inverse association in studies that did not (RR = 0.90, 95% CI = 0.78-1.04). In a separate meta-analysis, no significant association between overweight (25 kg/m(2) <= BMI <= 29.9 kg/m(2)), obesity (BMI >= 30 kg/m(2)) or excess weight (BMI >= 25 kg/m(2)) and PD risk was observed. Conclusion This meta-analysis does not support the notion that higher BMI materially increases PD risk. However, a week positive BMI-PD association that may be masked by confounders still cannot be excluded, and future prospective studies with a good control for potential confounding factors are needed.