Review Suggests Having IBD May Increase Risk of PD

The meta-analysis sought to clarify previous research, which has explored the idea that Parkinson disease (PD) is tied to inflammation in the gastrointestinal tract, noting that inflammatory bowel disease (IBD) has been implicated in neuroinflammation.

A recent review and meta-analysis suggests a link between Parkinson disease (PD) and inflammatory bowel disease (IBD) and calls for randomized controlled trials in order to gain a better understanding of shared disease processes.

The gut-brain axis—or the relationship between the enteric nervous system and the central nervous system (CNS)—has become a focus of researchers in recent years. Recent work has explored the idea that PD is tied to inflammation in the gastrointestinal tract, and IBD, an umbrella term which includes ulcerative colitis (UC) and Crohn disease (CD), has been implicated in neuroinflammation.

Writing in Neural Regeneration Research, the authors said they wanted to update what is currently known about this possible association, as previous studies have had conflicting results.

Using PubMed, Embase, and Cochrane databases, the authors retrieved observational studies of IBD and PD published from inception to October 2019. Case reports, letters, reviews, editorials, retrospective designs lacking controls, and genetic studies that only reported risk alleles were excluded. Studies were also excluded if they were judged to have a high risk of bias as assessed by the Newcastle-Ottawa Scale.

After an initial screening returned 1033 articles, 9 observational studies including 12,177,520 patients were included in the final analysis. One of the 9 studies was both a cohort and case-control study based on the same population. Of the 9 studies, 6 were cohort studies, 3 were case-control studies, and 1 was a cross-sectional study.

The studies came from Denmark, Sweden, the United States, Taiwan, and Switzerland. Researchers pooled the unadjusted and adjusted estimate effects separately, adjusted for confounders, and excluded heterogeneous studies.

Results showed:

  • The overall risk of PD was significantly higher in patients with IBD than in the general population (adjusted risk ratio [aRR], 1.24; 95% CI, 1.15-1.34; P < .001).
  • A meta-analysis of the temporal relationship illustrated the incidence of IBD as it related to PD diagnosis, with a significant increase before (adjusted HR [aHR], 1.26; 95% CI, 1.18-1.35; P < .001) and after (aRR, 1.40; 95% CI, 1.20-1.80; P < .001) the diagnosis.
  • After excluding a heterogeneous study, the pooled risk of PD development in patients with UC (aHR, 1.25; 95% CI, 1.13-1.38; P < .001) or CD (aHR, 1.33, 95% CI, 1.21-1.45; P < .01) was significantly increased.

By subgroup analysis, patients older than 65 with IBD (aHR, 1.32; 95% CI, 1.17-1.48) may have a higher risk of PD than those under age 65 (aHR, 1.24; 95% CI, 1.08-1.42).

In addition, patients with IBD who were not treated with anti–tumor necrosis factor-α or azathioprine had significantly higher PD risk (aHR, 1.6; 95% CI, 1.2-2.2).

However, there was no significant differences in risk between men and women.

The researchers noted that the data may not have contained complete insights into the timing of IBD and PD, since the studies that were reviewed were based on Medicare databases or hospital registries. Both diseases develop over years and may present with varying symptoms, which can make diagnosis challenging.

Our findings suggest an urgent need for an individualized screening strategy for patients with IBD,” wrote the authors, noting that the use of early anti-inflammatory treatments for IBD may lessen the risk of PD, although they cautioned that more research is needed.


Zhu Y, Yuan M, Liu Y, et al. Association between inflammatory bowel diseases and Parkinson's disease: systematic review and meta-analysis. Neural Regen Res. 2022;17(2):344–353. doi:10.4103/1673-5374.317981