• Posted July 19, 2023

Constipation May Be a Marker for Dementia Risk

Chronic constipation may not only be an indicator of gut health, but a potential warning sign of thinking declines, a preliminary study suggests.

Researchers found that among more than 110,000 middle-aged and older U.S. adults, those who were chronically constipated -- fewer than three bowel movements a week -- also showed signs of an "older" brain.

Compared with their counterparts who were regular, they typically performed worse on tests of memory and thinking -- equivalent to three extra years of aging. And they were 73% more likely to say their cognitive skills were waning.

The findings -- presented Wednesday at a meeting of the Alzheimer's Association in Amsterdam and online -- are considered preliminary. And they do not prove that constipation, per se, somehow causes the aging brain to deteriorate faster.

But experts said the findings add to evidence connecting gut health to brain health.

One possibility, researchers theorize, is that constipation and cognition are linked via the gut microbiome. That's the vast array of bacteria that naturally dwell in the intestines and play important roles in many bodily functions.

An explosion of research in recent years has been looking at links between the gut microbiome and various diseases, including degenerative brain diseases like Alzheimer's. The question is whether certain gut microbiome profiles -- an abundance of particular "bad" bacteria or short supply of some "good" ones -- might contribute to those health conditions.

One recent study, for example, found that people with early markers of Alzheimer's -- abnormal protein buildup in the brain -- also had gut microbiomes that looked different from those of other older adults.

In theory, constipation could be a symptom of a gut microbiome that is associated with poorer cognition. But that remains to be proven.

"It's unclear at this point whether constipation itself or the underlying cause of constipation -- whether it be disruptions in the gut microbiome or a change in diet -- is driving this association," said Claire Sexton, senior director of scientific programs and outreach for the Alzheimer's Association.

Sexton, who was not involved in the study, said that if people have chronic constipation, they can talk to their doctor about how to deal with it.

Dr. Dong Wang, the senior researcher on the study, made similar points.

"These results stress the importance of clinicians discussing gut health, especially constipation, with their older patients," said Wang, of Brigham and Women's Hospital and Harvard Medical School.

He added that people can prevent constipation and improve their gut health by eating plenty of fiber-rich foods like vegetables, fruits, whole grains and beans, and exercising regularly.

Other research has tied those same lifestyle habits to a lower risk of age-related cognitive decline and dementia.

Wang's team based its findings on data from three large studies that have been tracking over 100,000 U.S. medical professionals for decades. In 2012-2013, participants reported on their bowel habits, and between 2014 and 2017 they self-rated their cognitive function.

A subset underwent objective tests of memory and thinking skills between 2014 and 2018.

On average, researchers found, those objective scores were lower among people who'd reported chronic constipation -- having a bowel movement no more often than every three days -- compared to people who were like clockwork (one bowel movement per day).

Similarly, people with constipation gave lower ratings to their subjective cognitive abilities.

Next, the researchers dug into the microbe question. They found that people with constipation and worse cognition tended to have relatively few gut bacteria that produce butyrate -- an important fatty acid that helps control inflammation. Gut bacteria churn out butyrate when they break down fiber.

Two other studies presented at the conference back up the gut-brain link.

Researchers at UT Health San Antonio found that middle-aged and older adults with "poor cognition" tended to have low levels of certain good gut bacteria. Meanwhile, older adults with abnormal protein buildup in the brain (but no dementia symptoms) also showed depleted levels of certain good bacteria.

While the findings are intriguing, much more research is needed, Sexton said.

Researchers are a long way from proving that altering gut bacteria -- through diet, probiotics or other means -- can help keep the aging brain sharp.

The Alzheimer's Association is running a clinical trial testing the effects of a healthy diet (high in plant foods and fiber), exercise and other lifestyle measures in slowing older adults' cognitive decline.

Sexton said that will include a deeper dive into the gut-brain question -- looking at whether the lifestyle changes alter people's gut bacteria, and whether those changes correlate with their cognitive health.

Research presented at medical meetings is generally considered preliminary until published in a peer-reviewed journal.

More information

The Alzheimer's Association has advice on supporting brain health.

SOURCES: Claire Sexton, DPhil, senior director, scientific programs and outreach, Alzheimer's Association, Chicago; Dong Wang, ScD, MD, assistant professor, medicine, Brigham and Women's Hospital, Boston; presentation, Alzheimer's Association International Conference, Amsterdam and online, July 19, 2023