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New research links constipation with a higher risk of cognitive decline. Image credit: tifonimages/Getty Images.
  • In a series of new studies, researchers investigated the link between constipation and cognitive decline.
  • They found that one bowel movement every 3 days or less frequently is linked to higher levels of cognitive decline alongside certain changes in the gut microbiome.
  • Further studies are needed to see how these findings could inform treatments and prevention strategies for cognitive decline.

Around 16% of the global population experiences constipation. Risk factors for constipation include low levels of physical activity, female gender, residential location, and medical conditions, including depression, hemorrhoids, and some cardiovascular, gastrointestinal, and musculoskeletal conditions.

Chronic constipation occurs when a person has fewer than one bowel movement every 3 or more days. It has been linked to various health conditions, including anxiety and depression.

Studies show that constipation is a common complication of neurological conditions, such as Parkinson’s disease, and that it is linked to faster Alzheimer’s disease progression.

Understanding more about how constipation affects the neurological system — and the brain and cognition by extension — could aid the development of treatments and prevention strategies for cognitive decline and related conditions.

Recently, researchers investigated the link between constipation and cognitive decline. They found that having a bowel movement every 3 days or less frequently was linked to a 73% higher chance of subjective cognitive decline.

The studies were presented at the Alzheimer’s Association International Conference in Amsterdam, Netherlands, and online.

Other related studies also found that increases and decreases in certain gut bacteria are linked to dementia and cognitive decline.

“This research is a first step to investigating whether certain types of bacterial presence within our intestines protects our brains from certain types of cognitive diseases,” Dr. Thomas Gut, assistant professor at Donald and Barbara Zucker School of Medicine at Hofstra/ Northwell, not involved in this research, told Medical News Today.

“This research does not even begin to address the question of whether promoting certain types of bacterial colonization could be protective of memory and brain function but it does raise the question and creates a pathway for further research to follow.”

– Dr. Thomas Gut

For the study, the researchers examined data from 112,753 men and women. Data included information on their bowel movement frequency between 2012 and 2013 alongside self-assessments of cognitive function between 2014 and 2017.

A subgroup of 12,696 participants also underwent neuropsychological testing under the supervision of researchers. The participants further provided stool samples to assess levels of different bacteria.

Ultimately, the researchers found that people who had a bowel movement every 3 or more days had significantly worse cognition — equivalent to 3 years of additional aging — than those who had one bowel movement per day.

They also had a 73% higher risk of subjective cognitive decline and fewer microbes that produce butyrate, a marker of healthy bacteria that help digest dietary fibers.

The researchers further found that those who had more than two bowel movements per day had a slightly increased risk of cognitive decline and tended to have more pro-inflammatory species in their microbiome.

The researchers concluded that less frequent bowel movements are linked to worse cognitive function and that this link may be explained by changes in the gut microbiome.

Two other recent studies further investigated specific gut bacteria linked to increased dementia risk, as well as which gut bacteria may be neuroprotective.

In the first study, researchers assessed data from 140 cognitively healthy individuals with an average age of 56 years. Data included fecal samples and measures of Alzheimer’s protein biomarkers amyloid and tau from PET brain scans.

They found that higher levels of amyloid and tau were linked to lower levels of gut bacteria Butyricicoccus and Ruminococcus and higher amounts of Cytophaga and Alistipes. They noted that Butyricicoccus and Ruminococcus might have neuroprotective effects.

In a press release, the researchers suggested that the reduction of certain bacteria may increase gut permeability and the transport of certain metabolites to the brain, which could, in turn, increase the buildup of amyloid-beta and tau proteins.

They said that a next step for research would be to test whether introducing, increasing, or reducing certain gut microbes could beneficially change levels of amyloid and tau. If so, this could help in identifying potential new therapeutic approaches for Alzheimer’s.

In the second study, researchers examined fecal samples and cognitive test scores from 1,014 participants with a mean age of 52 years old. They split the cohort into groups according to their cognitive test scores and compared those scoring in the lowest 20% to those scoring the highest.

Ultimately, they found that individuals with the poorest cognition had lower levels of Clostridium and Ruminococcus and higher levels of Alistipes and Pseudobutyrivibrio than other participants.

The researchers noted that more research is needed to better understand the possible neuroprotective effects of these bacteria. However, they added that in the future, it may be possible to manipulate their abundance through diet and prebiotics to preserve brain health and cognitive function.

Medical News Today spoke with Dr. J. Wes Ulm, a bioinformatic scientific resource analyst, and biomedical data specialist at the National Institutes of Health, who was not involved in the research, about its limitations.

He said that while the studies show a correlation between constipation and cognitive decline, they do not demonstrate causation due to their preliminary nature.

“It’s likewise unknown if there is a causal relationship between certain dietary practices, such as fiber consumption or the use of probiotics or prebiotics, and the observed findings,” he noted.

“Furthermore, most of the observations of cognitive decline were subjective in the associated patient population, with only a relatively small sample undergoing objective testing of various means to more reliably corroborate such a finding,” Dr. Ulm added.

Dr. Ulm noted that although causation and mechanisms remain unclear, other studies show that contributors to chronic constipation, such as insufficient fiber intake, low fluid intake, and a sedentary lifestyle, are also linked to inflammation and neuropsychiatric conditions.

He added that while nutritional recommendations can be frustrating as they shift frequently according to scientific advances, overall, improving general health habits may reduce the risk of cognitive decline. Such habits include increasing the consumption of fruit, vegetables, fiber, and fluids and exercising more frequently.

Dr. Ulm concluded that it would be interesting to see what comes from this research — from basic treatments to reduce constipation to targeted modifications of the gut microbiome — and how these may help prevent dementia and cognitive decline in general.