No causal relationship found in study between IBS and Parkinson’s
Having irritable bowel syndrome likely not linked to increased disease risk
Having irritable bowel syndrome (IBS), a gastrointestinal disorder that may be linked to how the brain and gut communicate with each other, does not seem to increase a person’s risk for Parkinson’s disease, according to a new study of more than 400,000 people.
In an analysis, the researchers “did not find significant evidence of the causal relationship between IBS and Parkinson’s disease,” they wrote.
“Overall, we suggest that IBS status is not associated with the risk of developing [Parkingson’s], and that these findings provide valuable insights into the clinical management … of patients with IBS,” the team wrote.
Their study, “Association between irritable bowel syndrome and Parkinson’s disease by Cohort study and Mendelian randomization analysis,” was published in npj Parkinson’s Disease.
Constipation, an IBS symptom, can be early sign of Parkinson’s
The gut-brain axis, a two-way route of communication between the gut and the brain, is thought to play a role in how Parkinson’s develops. Alpha-synuclein, a protein that forms toxic clumps, travels from the gut’s lining to the brain, where it drives the onset of the disease’s symptoms.
Known simply as IBS, irritable bowel syndrome is a disorder of the gut that causes pain or discomfort in the abdomen, as well as bloating and altered bowel habits. The reasons behind IBS can be many. Because it can accompany anxiety and depression, it is possible that the gut-brain axis may be involved, too, according to scientists.
Many people with Parkinson’s experience digestive problems, such as constipation, in the early stages of the disease, sometimes before the hallmark motor symptoms manifest. While a link between Parkinson’s and IBS is plausible, “current studies … are limited and exhibit conflicting results,” the researchers wrote.
To fill this gap, a team from Zhengzhou University, in China, turned to Mendelian randomization. This method uses genetic data to determine if there is a causal link between an exposure — in this case, IBS — and an outcome, here, Parkinson’s, while making sure other factors don’t influence the results.
Their study included 426,911 people from the U.K. Biobank, a large database that collected health and genetic data from more than a half million people, ages 40 to 69, between 2006 and 2010. None of them had a diagnosis of Parkinson’s at entry to the database.
Some 19,768 participants (about 5%) were diagnosed with IBS before entry to the database. Compared with people without IBS, those with the condition were more likely to be female, less educated, and non-smokers. The IBS cohort, or group, also was reported to consume less alcohol, have poorer health, and have more coexisting conditions.
During an average follow-up of about 14 years, 2,321 people without IBS and 90 with the disorder were diagnosed with Parkinson’s. This translated into an incidence rate, or rate of new cases, that the researchers noted was lower among people with IBS.
IBS is not associated with an overall increased risk of [Parkinson’s].
The risk of developing Parkinson’s seemed to be about 23% lower in IBS patients, and even lower if they were diagnosed with irritable bowl syndrome after the year 2000.
However, when considering other factors, such as age, gender, ethnicity, education level, drinking, smoking status, and body mass index, this link became less clear or lost significance.
To confirm these findings, the researchers matched each person with IBS to five people without the condition based on age and sex. Among a total of 7,226 people with IBS and 36,130 people without IBS, 247 went on to develop Parkinson’s. Having IBS did not reduce the risk for Parkinson’s.
Mendelian randomization based on the presence of 16 single nucleotide polymorphisms — variations at a single base position in the DNA — associated with IBS did not find significant evidence of an overlap between IBS and Parkinson’s.
“IBS is not associated with an overall increased risk of [Parkinson’s],” the researchers wrote. But they noted that “more studies are needed in the future to further understand the association between IBS and [Parkinson’s].”
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