Parkinson’s Disease, Smoking, and Lower Endoscopy

ABSTRACT Parkinson’s disease (PD) is inversely associated with smoking. Whether this association is due to a causal relationship or to confounding by a covariate of smoking is still debated. The Institute for Health Metrics and Evaluation (IHME) released refreshed data on October 15, 2020. This study included that recently released data. The study included populations of the United States and ten U.S. states from 2004 to 2018. The ten U.S. states included the five states with the highest PD incidence rates in 2019 (Maine, Vermont, Kansas, Alaska, Missouri) and the five states with the lowest PD incidence rates in 2019 (Arkansas, Mississippi, South Dakota, Nebraska, Delaware). The study used scatter plots to explore the association between PD incidence and smoking and the association between PD incidence and a covariate of smoking, lower endoscopy utilization. For PD verses smoking, the results indicate that there is an inverse correlation for the United States, but there is no association for the ten states. The coefficient of determination (R 2 ) for the United States was 0.714 and ranged from a low of 0.004 for South Dakota to 0.613 for Mississippi. The average R 2 for the ten states was 0.357. For PD verses lower endoscopy, the results indicate that the best model fit to the data is a polynomial. When the fitting curve examined in the regression analysis was a 3rd order (cubic) polynomial, there was a positive correlation between PD and lower endoscopy for the United States and for all ten states. The R 2 for the US was 0.971 and ranged from a low of 0.709 for Alaska to 0.970 for Kansas. The average R 2 for the ten states was 0.878. The results suggest that the inverse association between PD incidence and smoking is confounded by a positive association between PD and lower endoscopy utilization. Further investigation of a possible relationship between PD incidence and lower endoscopy utilization is warranted and may provide a means for reducing PD incidence.