Probiotics are well-known for their digestive health perks. But scientists have wondered if the "good" bugs might also affect our brains, since the brain and the gut appear to be closely connected.
Now, a study suggests that taking a daily probiotic supplement may slightly improve memory and thinking skills in older adults. According to the Iranian researchers, the beneficial bacteria might potentially protect against Alzheimer’s disease and other forms of cognitive decline, although more studies are needed.
Other research has shown that mice fed probiotics had improved thinking and memory skills. Until now, however, no placebo-controlled trials had been conducted on people, the authors say. For their study, they gave 60 men and women diagnosed with Alzheimer’s disease either a daily glass of plain milk or milk treated with probiotics—including Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus fermentum, and Bifidobacterium bifidum.
At the beginning and end of the 12-week study, the participants took tests designed to measure brain function, such as giving the current date, counting backward from 100 by sevens, naming objects, repeating a phrase, and copying a picture. They also gave blood samples to measure other metabolic changes.
Over the 12 weeks, those in the probiotic group reported no side effects and their average cognitive score rose slightly—from 8.7 to 10.6 out of a 30-point maximum. In the placebo group, scores went down a bit, from 8.5 to 8.0.
This is only a mild improvement, say the study authors, and all of the participants remained severely impaired. But the findings are still important, they add, because they are the first to show any brain benefits from probiotics in humans. The authors say they have no financial conflicts of interest, although a supplement maker donated the probiotics for the study.
In their conclusion, the researchers wrote that “probiotic supplementation shows some hopeful trends that warrant further study to assess if probiotics have a clinically significant impact on the cognitive symptoms.” Larger patient groups, and longer study periods, could show if the small, but statistically real effects seen here could become stronger over time, they say.
The study, which was published yesterday in the journal Frontiers in Aging Neuroscience, revealed other probiotic-related perks, as well: Daily consumption was associated not just with improved memory and thinking, but lower levels of two types of cholesterol (triglycerides and VLDL, or very low-density lipoprotein) and two common measures of insulin resistance as well.
It also appeared to lower levels of a marker of inflammation found in the blood of people with Alzheimer’s (called high-sensitivity c-reactive protein)—although it had no effect on other biomarkers of cell damage or inflammation.
"These findings indicate that change in the metabolic adjustments might be a mechanism by which probiotics affect Alzheimer's and possibly other neurological disorders," said senior author Mahmoud Salami, PhD, professor of physiology at Kashan University in Iran, in a press release. "We plan to look at these mechanisms in greater detail in our next study."
Louisiana State University neurology professor Walter Lukiw, PhD, said in a press release that the study provides important evidence for the theory that the gut microbiome can play a role in neurological functioning—and that probiotics seem to influence both.
“This is in line with some of our recent studies which indicate that the GI tract microbiome in Alzheimer's is significantly altered in composition when compared to age-matched controls,” said Lukiw, who reviewed the new study but was not involved in the research.
As another potential explanation for the link between brain and gut, Lukiw cited evidence that “both the GI tract and blood-brain barriers become significantly more leaky with aging,” potentially allowing toxic bacteria and other substances from the GI system to access the central nervous system.
Healthy adults can safely consume up to 20 billion CFUs of probiotics a day, says Health’s medical editor Dr. Raj. If you want to try a supplement, check out our recommendations and talk to your doc about what products and dosage she recommends.
Of course, you can also get the beneficial bugs by eating fermented foods. To work more of them into your diet, here's a list of 9 probiotic foods other than yogurt.