There is some plausibility here... but not all studies point the same way. May be some biological similarities, genetic homogeneity, or inflammation in the gut per se as a risk factor. The strengthening of association with hypertension and CAD here is a bit strange. We previously published on Crohn's and PD genetic comorbidity (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3888265/)
Inflamm Bowel Dis. 2016 Feb 24. [Epub ahead of print]
Lin JC, Lin CS, Hsu CW, Lin CL, Kao CH.
Inflammatory bowel disease (IBD) is a chronic inflammatory disorder. Previous studies have suggested that chronic systemic inflammation increases the risk of Parkinson's disease (PD). This study examined the effects of IBD on the development of PD.
In a nationwide population-based cohort of 23.22 million insured residents of Taiwan aged ≥ 20 years, we compared people diagnosed with IBD during 2000 to 2011 (n = 8373) with IBD-free individuals. Patients with PD were identified in the National Health Insurance Research Database. Using univariable and multivariable Cox proportion hazard regression models, we estimated the adjusted hazard ratio (aHR) for PD with a 95% confidence interval (CI) with adjustment for age, sex, and comorbidities.
In the cohort, IBD was associated with an increased incidence of PD (crude hazard ratio = 1.43, 95% CI = 1.15-1.79). The risk was highest among individuals with Crohn's disease (aHR = 1.40, 95% CI = 1.11-1.77). In the multivariable model, the risk of PD was increased for men (aHR = 1.28, 95% CI = 1.05-1.56) and higher for patients with hypertension (aHR = 1.72, 95% CI = 1.33-2.24), coronary artery disease (aHR = 1.31, 95% CI = 1.04-1.66), or depression (aHR = 2.51, 95% CI = 1.82-3.46).
We suggest that IBD is associated with an increased risk of PD. Patients with IBD should be aware of the potential risk for PD development.