Cropland associated with risk of Parkinson's disease in the northern Great Plains

Introduction

We sought to identify regional associations between cropland density and crop types and PD in the U.S.

Methods

We conducted a population-based study of 21,639,190 Medicare beneficiaries, 89,790 with incident PD in 2009. We used county-level geographic weighted regression (GWR) to identify region(s) of the U.S. where the association between PD RR and cropland density was strongest. In a broad region identified by GWR in which cropland density was associated with PD, we performed logistic regression using individual-level beneficiary data (2733 cases and 805,984 non-cases) with high-resolution cropland density data. We adjusted for age, sex, race, smoking, healthcare utilization, and PM_2.5 (particulate matter <2.5 μm). We then explored PD-cropland associations for each type of crop within a subregion, in which the association was the strongest.

Results

GWR identified a 9-state region in the Great Plains in which county-level cropland density and PD RR were associated. Within this region, the strongest GWR coefficients centered around the Williston Basin. High-resolution analysis demonstrated an association between cropland density within a 5-mile radius of residential zip+4 and PD. When comparing the highest to lowest quartile of cropland density, the odds ratio (OR) for PD was 1.14 (95 % confidence interval [CI] 1.01–1.27) in the 9-state region and 1.99 (95 % CI 1.09–3.61) in the Williston Basin. In the Williston Basin, percentage of sunflowers, winter wheat, and alfalfa within 5 miles of a beneficiary's zip+4 was associated with PD.

Conclusion

We identified a region-specific association between cropland and crop type and PD in the Williston Basin.