A Common Probiotic Could Boost Brain Health in Older Adults

While the benefit was seen only in individuals with mild cognitive impairments, these findings lend more insight into the gut-brain connection.

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It’s said the way to one’s heart is through the stomach, but it looks like the way to a healthy brain is by dropping a deuce regularly. According to new research presented at the Alzheimer’s Association International Conference in Amsterdam this week, chronic constipation appears to be linked to worsening cognitive abilities, likely due to an imbalance of gut bacteria causing inflammation.

While the study has yet to be peer-reviewed, it emphasizes a link between cognition and the microbiome — microorganisms like bacteria, viruses, and fungi living rent-free in and on our bodies — that hasn’t gone unnoticed. There’s still a whole lot we don’t know about the microbiome, but what we do know suggests these microscopic houseguests can be manipulated to improve our own health.

To offset cognitive decline, it could be as simple as a daily probiotic, says Mashael Aljumaah, a doctoral student at the University of North Carolina at Chapel Hill (UNC) and North Carolina State University. In findings presented Monday at the American Society for Nutrition in Boston, Aljumaah and her colleagues at UNC and Kent State University in Ohio found that for older adults, a daily probiotic containing gut-friendly Lactobacillus rhamnosus helped improve mild cognitive impairment by resetting the imbalance in gut bacteria.

While further research is needed, these findings lend to new avenues of tackling cognitive decline whether due to aging or neurological conditions like dementia and Alzheimer’s disease.

Twice a day for three months

Over the years, there have been many studies looking at how gut dysbiosis — or the imbalance of gut bacteria — can affect cognitive function through the brain-gut axis. Research in mice has found that simply transplanting gut bacteria from young, healthy animals to older ones appears to reverse age-related cognitive decline. In humans, a 2021 meta-analysis found that probiotic supplementation may improve cognitive issues in adults resulting from a myriad of conditions from chronic fatigue syndrome to HIV as well as aging.

In 2017, John Gunstad, Aljumaah’s co-researcher and an assistant professor of psychology at Kent State University, recruited middle-aged (between ages 52 and 59) and older adults (between ages 60 and 75) in a study to evaluate whether probiotics containing Lactobacillus rhamnosus GG (or LGG) could help those dealing with mild cognitive impairment.

“One of the strengths of this study is that we compared people with mild cognitive impairment — one of the early stages — to healthy individuals,” Aljumaah tells Inverse. “A lot of published studies compare [individuals with mild cognitive impairment] to other forms of severe neurological disorder. But this study gives us the resolution to see the changes in the gut microbiome that are associated with the early stages of cognitive decline.”

For study participants who had mild cognitive impairment and took the probiotic Lactobacillus rhamnosus GG (LGG) for three months, cognitive scores increased. This cognitive improvement was also associated with changes in their gut microbiome.

Mashael Aljumaah / University of North Carolina at Chapel Hill and North Carolina State University

For the next three months, these 169 individuals received either an LGG probiotic or placebo twice daily; the participants didn’t know which they were getting. This group was further subdivided based on cognitive status — intact or impaired. The composition of the participants’ gut microbiomes was checked before and after the trial by sifting through their poop.

“The first aim of the study was to identify what are the key factors, what are the key changes compared to healthy individuals,” says Aljumaah.

One key change the researchers saw was in a community of gut bugs called Prevotella, an anaerobic bacteria that grows in regions of the gastrointestinal tract where oxygen is scarce. On its own, Prevotella isn’t necessarily a bad microbe, but in those with impaired cognition, there was way more of it compared to the cognitively intact folks.

After the three months of LGG, Prevotella numbers dipped down just as cognitive scores of those with mild impairments went up. Aljumaah says it’s not entirely clear why this association occurred, but it might have to do with metabolites produced by the microbiome that affect brain chemistry and neurological activity. In further studies she and her colleagues did, they identified pathways Prevotella may be influencing that involve the neurotransmitters glutamate and gamma-aminobutyric acid (or GABA).

Eat more fermented foods

If you’re hoping that popping LGG on the daily will turn you into Bradley Cooper in Limitless, don’t rush off to GNC just yet. Aljumaah says the improvement in cognitive function was only noticed among those who had mild impairments.

If someone had no cognitive impairments to start with, they didn’t seem to benefit from the probiotics, says Aljumaah. “When you have a compromised baseline, you actually benefit more from using a probiotic — that’s something that’s been observed in previous studies.”

But you should still do whatever you can to promote and maintain a healthy gut. A diet rich in prebiotic and fermented foods keeps your gut balanced and mental health in check, as one 2022 study published in the journal Molecular Psychiatry reported.

Aljumaah believes a shifting gut microbiome could be used as an indicator of when cognitive function goes awry. She says there’s still more to learn about the ecosystem of dysbiosis, what sort of biochemical pathways are unleased, and how to specifically target them early before something like mild cognitive impairment becomes more severe and potentially debilitating.

“There’s never only one cause, one pathway,” says Aljumaah. “While we’re hoping to understand one piece of the puzzle, there’s a pool of scientists around the world. Hopefully, together, we can get a better picture of how the gut microbiome affects our mental and cognitive health.”

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