Your Gut Could Be the Key to Early Alzheimer’s Detection, Study Finds
New research links gut microbiome to Alzheimer’s disease risk.
People with early markers of Alzheimer’s disease had similar gut microbiome compositions that were different from those without early signs of the condition.
Experts explain the findings.
Alzheimer’s disease is a complex condition, and scientists are still trying to figure out why people develop the disease. Now, a new study suggests the bacteria in your gut may play a role in whether you develop Alzheimer’s.
The study, which was published in the journal Science Translational Medicine, looked at the gut microbiome and composition of 164 older people (ranging in age from 68 to 94) with normal cognition. The researchers checked for the presence of proteins in participants’ brains associated with Alzheimer’s disease—amyloid and tau—and had them complete cognition tests to try to identify those who may have early markers of Alzheimer’s disease.
The scientists then used fecal samples to compare the bacteria found in the guts of 49 people with markers for Alzheimer’s disease with those without markers.
The researchers found that people with preclinical Alzheimer’s disease (meaning: They don’t yet have symptoms of the condition) had different gut microbiomes than those without the disease. Specifically, people who were in the preclinical stages of Alzheimer’s often had higher levels of bacteria that are involved in breaking down the amino acids arginine and ornithine, which are involved with protein buildup (Alzheimer’s disease is thought to be caused by the build-up of proteins in and around brain cells). Those who didn’t have preclinical Alzheimer’s disease typically had more bacteria that are involved in glutamate degradation, which can protect neurons (nerve cells that act as messengers in your body).
The researchers also took that information and compared it with risk factors, including a family history of Alzheimer’s disease, the study participants’ age, genetics, and whether they had diabetes, along with their brain images to try to predict who was in the early stages of Alzheimer’s—and it was pretty accurate.
“Gut microbiome correlates of preclinical Alzheimer’s disease neuropathology may improve our understanding of Alzheimer’s disease etiology and may help to identify gut-derived markers of Alzheimer’s disease risk,” the researchers concluded.
But what does your gut have to do with your Alzheimer’s disease risk, and what can doctors do with this information? Here’s what you need to know.
What does your gut have to do with your brain?
Your gut and brain are in two different areas of your body, but research has shown they can influence each other. There’s something known as the gut-brain axis, which is basically communication between your brain and gut that links the emotional and cognitive centers of your brain with some functions in your intestine.
Some examples of your gut-brain axis at work: Getting diarrhea or constipation when you’re stressed, or feeling butterflies in your stomach when you’re nervous.
“If you actually look, the most innervated part of your body after your brain is your gut,” says study co-author Beau M. Ances, M.D., Ph.D., a neurologist at Washington University Physicians. “There is a large connection between the two and they’re constantly talking.”
Researchers are still exploring how the gut-brain axis may influence a host of diseases, including irritable bowel syndrome (IBS), depression, and obesity.
What’s the relationship between your gut and brain in Alzheimer’s disease?
It’s not entirely clear at this point. Dr. Ances says it’s hard to tell if the gut is influencing the brain or the brain is influencing the gut. Meaning, it’s unclear right now if the gut microbiome changes are due to changes in the brain or if the gut changes are actually contributing to Alzheimer’s disease.
The findings are “very promising, but it is limited because it is correlational and includes people after the disease has already developed,” says Martin Blaser, M.D., chair of the Henry Rutgers Chair of the Human Microbiome at the Rutgers Robert Wood Johnson Medical School. “But, if confirmed and extended, [the findings] suggest that ways to control or harness the microbiome may be useful to prevent Alzheimer's disease onset or progression.”
The connection is also being explored beyond this study.
Research suggests that chronic inflammation in the brain can raise the risk of developing Alzheimer’s disease by causing damage and death to neurons. Research has also indicated that high-fiber foods like whole grains, fruits, and vegetables, may help reduce inflammation. The National Institute on Aging (NIA) notes that certain gut bacteria convert the fiber from these foods into compounds called short-chain fatty acids (SCFAs), which can fight inflammation and have been found to improve memory in animals.
Results of one mouse study published last year, for example, found that a high-fiber diet changed the types of bacteria in the gut microbiome, increased the production of SCFAs, and reduced the expression of some genes that control inflammation in the brain.
“We’re just seeing that there’s a close gut-brain connection in terms of physical health over the course of the aging process,” says David Merrill, M.D., Ph.D., a geriatric psychiatrist and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center in Santa Monica, CA.
What happens now?
It’s not entirely clear. The latest study found that both healthy people and those with preclinical Alzheimer’s disease had different gut bacteria despite eating basically the same diet.
But Dr. Ances says his work could lead to a future diagnostic test that would be easier to administer and more accessible to the general public. “We’re all producing stool, so it’s pretty easy to assess and evaluate,” he says.
It may also help people with early markers of Alzheimer’s disease to take steps to slow the progression of the disease or even prevent it. “There are lots of therapies out there, including probiotics,” Dr. Ances says. “The question would be, ‘Could we alter the gut microbiome, bring some things down and increase others that could lead to changes in amyloid or tau?’”
Dr. Ances and his team have also started a five-year follow-up study to see whether the differences in the gut microbiome are a cause or effect of the brain changes seen in early Alzheimer’s disease. “It’s very interesting to learn about how our brain and gut are talking,” he says.
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