How Gut Bacteria May Play a Role in Brain Health

New research presented at the Alzheimer’s Association’s international conference in Amsterdam on Wednesday highlights a growing body of evidence linking the microbiome to their brain health.

A study found that chronic constipation was linked to worsening cognitive abilities – the equivalent of three years of aging – while two other studies have shown that certain gut bacteria are associated with dementia risk.

The three studies, which have yet to be published in peer-reviewed journals, point to a possible role that a buildup of “bad” bacteria in the gut could play in cognitive health.

“We know that it is essential for good overall health to regularly eliminate waste from the body. If that doesn’t happen, we risk retaining toxins that negatively impact our health in a variety of ways,” said Christopher Weber, director of global science initiatives for the Alzheimer’s Association, who was not involved in the study. research. “While more research is needed, this is a fascinating start.”

When the “bad” bacteria invade the “good” ones

Chaoran Ma, an assistant professor of nutrition at the University of Massachusetts Amherst, led the Constipation and Cognitive Decline Study, which analyzed six-year stool and cognition data from 110,000 people from three long-term studies.

People with chronic constipation – defined as having a bowel movement every three days or more – were found to have “significantly” worse cognition, equal to three years of aging, compared to those who could go once a day, according to research.

People with chronic constipation also had more bacteria that cause inflammation in their intestines and fewer bacteria that break down dietary fiber, said Ma, who was a researcher at Brigham and Women’s Hospital and Harvard Medical School in Boston when the search has been completed. The research showed correlation, not causation, which means the study does not prove that constipation causes such problems.

Researchers aren’t sure why constipation can affect the brain this way, but they think a buildup of “bad” bacteria overwhelms the protective “good” bacteria, Weber said.

Ma said the findings are particularly important for older people, who are more likely to suffer from constipation due to lack of exercise, use of certain medications and a low-fiber diet.

Two other studies presented at the conference, both conducted by researchers at UT Health San Antonio in Texas, found that specific gut bacteria were associated with an increased risk of dementia in cognitively healthy adults. Other gut bacteria, they found, had protective effects.

Together, the findings join a growing body of data on what scientists call the gut-brain axis – the two-way communication pathway that connects the functions of the gastrointestinal tract and the brain via the nervous, immune and hormonal systems and is involved in a variety of processes, from metabolism stress.

A better understanding of the axis could help scientists develop new ways to prevent and treat Alzheimer’s disease and other dementias before symptoms even appear.

“It’s important to recognize that all of our bodily systems are connected and work together,” Weber said. “If one of them is not working well and is not properly diagnosed and treated, it can have significant health consequences for other parts of the body.”

A biomarker of dementia in the gut?

Previous research has found that people diagnosed with Alzheimer’s disease, along with obesity, diabetes, irritable bowel syndrome and Parkinson’s disease, have less diverse gut microbiomes compared to those who do not have the disease.

A study conducted in Japan and published last year in the journal CNS Neurosciences and Therapeutics found that constipated Alzheimer’s patients experienced cognitive decline twice as fast as non-constipated patients.

However, less is known how — and if — doctors will one day be able to use these gut changes to reliably detect dementia in people who still have healthy brains or treat it in those who already have symptoms.

“Every person seems to have a unique microbiome, almost like a fingerprint,” said Dr. Monia Werlang, a gastroenterologist and assistant clinical professor at the University of South Carolina Greenville School of Medicine. “Scientists are still learning how to manipulate it to promote health and modify disease. Targeting the microbiome is promising, but there are many unknowns, especially given the variability from person to person.

Perhaps the biggest unknown is whether Alzheimer’s disease causes bacterial changes in the gut or whether bacterial changes in the gut, caused by constipation, for example, cause Alzheimer’s disease, a said Rima Kaddurah-Daouk, co-principal investigator at Alzheimer’s Gut Microbiome Projecta collaborative research initiative that maps the gut-brain axis and explores how diet and other lifestyle interventions influence cognition.

Zooming in even further, are the bacteria themselves toxic to the brain, or are some by-products of bacteria to blame?

“The bacteria that live with us are our partners, for better or for worse. Together we supplement each other’s metabolism and produce a host of chemicals,” said Kaddurah-Daouk, who is also a professor of psychiatry and behavioral sciences at Duke University School of Medicine in North Carolina. “The new research is a good first step, but we need to get down to the molecular level and connect the dots.”

For example, a reduction in a type of bacterial byproduct, called butyrate, as detected in Ma’s study may partly explain why constipation is associated with lower cognition.

Butyrate is produced in the gut when certain bacteria break down dietary fiber. It interacts with the immune system and helps reduce inflammation in the brain and spinal cord, Ma said. Butyrate also protects the blood-brain barrier, helping it better block toxic molecules from entering the brain.

When there are fewer butyrate-producing bacteria, the brain becomes more vulnerable to “bad” molecules that invade it and could impair cognition. The natural aging process also promotes an increase in inflammation-causing bacteria, which can lead to a ‘leaky gut’, further allowing toxic chemicals to enter the brain, according to a study published last year. in the journal. Nutrients.

Although a “healthy” gut microbiota has not yet been defined, there is ample evidence that balance is essential. In fact, an imbalance in the gut, known as dysbiosis, has been linked to the development of anxiety, obesity, diabetes, depression, multiple sclerosis, chronic fatigue syndrome and other disorders, according to the same article.

More work is needed before experts can use the gut microbiome as a screening tool for Alzheimer’s disease and other dementias, which would be less invasive and more convenient than the brain scans or spinal taps currently used to diagnose disease.

Dr. Shae Datta, a neurologist and co-director of the NYU Langone Concussion Center, said having a biomarker like gut bacteria could “open a window into dementia that could possibly help us start patients on drugs and ways.” preventative lifestyle changes earlier, “which is essential for the treatment of Alzheimer’s disease.

Studies consistently show that exercise, get enough sleep, and have a good diet made up of fiber-rich foods (especially a mediterranean diet) will not only prevent constipation, but also promote brain health.

“It’s time to stop seeing Alzheimer’s disease as just a disease of the brain, and instead see it as a disease of the brain, liver and gut,” Kaddurah-Daouk said. “Changing your lifestyle for the better – eating well, exercising, relieving stress – is more effective than any pill available for Alzheimer’s disease today.”

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