Cognition and Constipation

Studies probing the connection between the microbiome and cognitive decline deepen our understanding of the gut-brain axis.

Constipation is an unpleasant symptom that most of us have experienced at some time in our lives. Although annoying, it has generally been considered relatively harmless, but now, according to research presented at the Alzheimer’s Association International Conference held in Amsterdam July 16–20, experiencing less frequent bowel movements is associated with cognitive decline. The study looked at 515 people around 67 years old who suffered chronic constipation—defined as having no more than one bowel movement every three days or more—and found they showed worse cognition, about equal to gaining three years of aging, and had a 73 percent higher chance of subjective cognitive decline. 

This new finding adds to the growing body of data about the relation of the gut-brain axis and cognition. At Nutrition 2023, the annual meeting of the American Society of Nutrition, held this July in Boston, a team of researchers presented a study that found that taking a probiotic could help prevent the decline in memory and thinking which occur during aging. And in a study published online August 9th in the journal Neurology, researchers from the University of Minnesota, University of California, Davis, and the University of Mississippi Medical Center found that people 45 and older who took proton pump inhibitors for four-and-a-half years or more (a common class of drugs used to treat acid reflux or heartburn) may have a higher risk of dementia compared to people who do not take these medications.

Data from 110,000 people

Approximately 16 percent of the world’s population struggles with constipation. That prevalence is even higher among older adults who have fiber-deficient diets, who don’t exercise enough, or who use certain constipating drugs to treat other medical conditions. Chronic constipation has already been associated with long-term health issues like inflammation, hormonal imbalances, anxiety, and depression. And now we can add dementia to that list. 

“Our study provides first-of-its-kind evidence of abnormal intestinal function being linked to cognitive decline.”

To study the relationship between chronic constipation and dementia, Chaoran Ma, a former research fellow at Brigham and Women’s Hospital and Harvard Medical School and current assistant professor at University of Massachusetts, assessed three prospective cohort studies of more than 110,000 people in the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study. Ma and team collected data on all participants’ bowel movement frequency in 2012–2013 and their self-assessments of cognitive function from 2014 to 2017. Objective cognitive function was measured between 2014 and 2018 in a subgroup of 12,696 participants. 

In an email Ma wrote, “Our study provides first-of-its-kind evidence of abnormal intestinal function being linked to cognitive decline.” They found that people who had specific microbial profiles in their gut—specifically, more bacteria that can cause inflammation and fewer bacteria responsible for digesting dietary fibers—tended to have less frequent bowel movements and worse cognitive function. 

“Our findings support considering constipation as a risk factor for cognitive decline,” Ma says, adding that unhealthy microbial profiles in the gut may explain the association between abnormal intestinal function and cognitive decline.

When asked what mechanism of action links chronic constipation to dementia, Ma said very broadly, “perturbations in the gut microbiome may partially explain the mechanistic link between variations in intestinal motility patterns and cognitive function.” 

It remains to be seen what the specific perturbations are to the gut flora and how they drive cognitive function declines over time. More importantly, we don’t yet know how to intervene with lifestyle adjustments to diet or medical interventions for the gut that would help people keep their brains healthier longer. 

So what can you do now?

Commenting on the study, Maria C. Carrillo, the Alzheimer’s Association chief science officer, who was not involved in the research, told that the research reported by Ma and colleagues tells us more about the importance of clearing toxins from the body and the tight connection between the brain and gut that we are only beginning to understand. 

“Once we recognize nutrition and hydration as key to overall health, including brain health, then it makes sense to take this one step further and think of the other ways our bodies eliminate waste. That includes urination and bowel movements. When you are constipated, not only are you likely not getting what you need to stay healthy—relaxation, good nutrition and hydration, active lifestyle—you probably are also not removing toxins and bad microbiota from your system, which could impact your brain directly or through increased inflammation in the body,” Carrillo says. 

“Eating well and taking care of your gut may be a pathway to reduce risk of dementia.”

Carrillo notes that there are many unanswered questions about the connection between the health of our digestive system and our long-term cognitive function, and that answering these questions may uncover novel therapeutic and risk-reduction approaches for Alzheimer’s and other dementias. To study this relationship further, she says that the Alzheimer’s Association U.S. Study to Protect Brain Health Through Lifestyle Intervention to Reduce Risk (U.S. POINTER), with support from the U.S. National Institutes of Health, is examining the impact of behavioral interventions on the gut-brain axis to better understand how engaging in healthier habits impacts microorganisms in the gut and how changes in gut bacteria relate to brain health.

While we await the results of the POINTER-Microbiome study, people should talk to their doctor about their digestive health and ways to alleviate constipation, such as increasing dietary fiber and drinking more water. Eating well and taking care of your gut may be a pathway to reduce risk of dementia,” Carrillo says. She notes that there were several studies presented on gut health and cognition at the Alzheimer’s conference in Amsterdam. “Besides the constipation study, two other studies found that certain gut bacteria were associated with dementia risk.” 

While it is true that these studies on the gut and cognition are not definitive, there is enough evidence that there is a link between brain health and gut health. So, listen to it and take care of your gut. Eat more fiber, drink more water, exercise more, and ask your doctor about probiotics.

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