Infrequent bowel movement tied to cognitive decline

A study presented at AAIC 2023 has shown a link between less frequent bowel movement (ie, one every 3+ days) and cognitive function in adults.

“We found that less frequent bowel movements were associated with worse cognitive function,” noted study investigator Dr Chaoran Ma from the University of Massachusetts Amherst, Massachusetts, US.

Ma and colleagues evaluated >110K participants from three prospective cohort studies: Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-up Study. They collected data on bowel movement frequency in 2012–2013 and participants’ self-assessments of cognitive function in 2014–2017. [AAIC 2023, abstract 73719]

Compared with those with once-daily bowel movement, participants with less frequent bowel movement had significantly worse cognition, equivalent to 3 years more of chronological cognitive ageing (95 percent confidence interval [CI], 1.2–4.7; p for nonlinearity=0.04). For learning and working memory, the poorer cognition among those with less frequent bowel movements equated to 7 years of cognitive ageing (95 percent CI, 2.5–11.6; p for nonlinearity=0.01).

In the pooled analysis, less frequent bowel movement was associated with 73 percent higher odds of subjective cognitive decline (95 percent CI, 1.60–1.86; p for nonlinearity<0.001). These associations were generally consistent across the three cohorts (p for nonlinearity<0.001 for all).

Bowel movement frequency and subjective cognition were significantly associated with the overall variation of the gut microbiome (p<0.005 for both) and specific microbial species. Gut microbes that were in abundance in both participants who had bowel movement every 2+ days and those who had worse cognitive function were Firmicutes bacterium CAG 110, Eisenbergiella massilliensis, and Eubacterium siraeum.

“Butyrate producers were depleted in those with less frequent bowel movements and worse cognitive function, while a higher abundance of dysbiosis-related, pro-inflammatory species was associated with bowel movement frequency of ≥2/day and worse cognitive function,” said the researchers.

Gut health important for brain health

“[The findings suggest that] the gut microbiome may be a mechanistic link underlying the association between intestinal motility patterns and cognitive function,” said the researchers.

“These results stress the importance of clinicians discussing gut health, especially constipation, with older patients,” noted senior study investigator Dr Dong Wang from Harvard T.H. Chan School of Public Health, Boston, Massachusetts, US, in a press release.

“Interventions for preventing constipation and improving gut health include adopting healthy diets enriched with high-fibre and high-polyphenol foods such as fruits, vegetables, and whole grains,” Wang continued. Additionally, it is important to take fibre supplements, drink plenty of water daily, and engage in physical activity regularly.

Dr Heather Snyder, Alzheimer’s Association Vice President of Medical and Scientific Relations, echoed Wang. “[P]eople should talk to their doctor about their digestive health and ways to alleviate constipation, such as increasing dietary fibre and drinking more water. Eating well and taking care of your gut may be a pathway to reduce risk of dementia.”

It’s all connected

“Our body systems are all interconnected. When one system is malfunctioning, it impacts other systems. When that dysfunction is not addressed, it can create a waterfall of consequences for the rest of the body,” Snyder said.

"A lot of questions about the connection between digestive health and long-term cognitive function remain unanswered," Snyder continued. “Answering these questions may uncover novel therapeutic and risk-reduction approaches for Alzheimer’s and other dementias.”