Association between Parkinson's disease and risk of colorectal cancer

Abstract Background Growing evidence has reported that gut microbiota is involved in pathogenesis of Parkinson's disease (PD) and colorectal cancer (CRC), and the association between PD and CRC does not reach a consensus. In order to explore their correlation, herein we summarize the epidemiological evidence and included relevant studies to perform a meta-analysis. Methods A comprehensive literature search for relevant articles published was performed in Medline, Web of Science and Embase up to June 30, 2016. The pooled risk ratio (RR) with 95% confidence intervals (CI) was used to estimate the effects and calculated using the method of generic inverse variance with the Random-effects model. Results Thirteen studies were included and analyzed in this meta-analysis. The pooled result of 11 cohort studies and 2 case-control studies comprising 343,226 PD patients showed that patients with PD had a decreased risk of CRC (RR: 0.79, 95% CI: 0.66–0.93, P = 0.006). Further subgroup analyses performed in Western population revealed that the significant inverse association between PD and risk of CRC was not undermined by many factors, including study design, tumor location, gender and quality of the study. Conclusion Patients with PD was significantly associated with a decreased risk of CRC in Western population. Future studies are warranted to further clarify this association in Asian population.