Body mass index and the risk of Parkinson disease

<b>Objective: </b> To examine the association between body mass index (BMI) and the risk of Parkinson disease (PD). <b>Methods: </b> Study cohorts included 22,367 Finnish men and 23,439 women 25 to 59 years of age without a history of PD at baseline. Hazards ratios (HRs) of incident PD were estimated for different levels of BMI. <b>Results: </b> During a mean follow-up period of 18.8 years, 272 men and 254 women developed incident PD. After adjustment for confounding factors (age, study years, systolic blood pressure, total cholesterol, education, leisure-time physical activity, smoking, and alcohol, coffee, and tea consumption), the HRs of PD at different levels of BMI (&lt;23, 23 to 24.9, 25 to 26.9, 27 to 29.9, and ≥30 kg/m²) were 1.00, 1.97 (95% CI: 1.21 to 3.22), 1.83 (95% CI: 1.12 to 2.99), 2.34 (95% CI: 1.45 to 3.78), and 2.44 (95% CI: 1.44 to 4.15) in men, and 1.00, 1.50 (95% CI: 0.95 to 2.37), 1.65 (95% CI: 1.05 to 2.59), 1.79 (95% CI: 1.15 to 2.80), and 1.77 (95% CI: 1.12 to 2.78) in women, and 1.00, 1.70 (95% CI: 1.23 to 2.37), 1.70 (95% CI: 1.23 to 2.37), 2.02 (95% CI: 1.46 to 2.79), and 2.03 (95% CI: 1.44 to 2.85) in men and women combined (adjusted also for sex). In both sexes combined, the multivariate-adjusted direct association between BMI and the risk of PD was present both in subjects aged 25 to 49 years and 50 to 59 years, in never smokers and smokers and in participants diagnosed PD before and after 65 years of age. <b>Conclusion: </b> Body mass index is associated with a risk of Parkinson disease. The effect is graded and independent of other risk factors.