Researchers from Iran show in the first human trial that probiotics appear to improve brain cognition in humans.
The study, “Effect of Probiotic Supplementation on Cognitive Function and Metabolic Status in Alzheimer’s Disease: A Randomized, Double-Blind and Controlled Trial,” was published in the open-access journal Frontiers in Aging Neuroscience.
While probiotics (live bacteria and yeast dietary supplements that are good for your health, especially your digestive system) offer partial protection against several disorders, such as inflammatory bowel disease, allergies, and periodontal disease, their effect on cognition remained a hypothesis.
This is because researchers discovered a communication platform between the intestinal microbiome, the gastrointestinal tract, and the brain. This two-way communication is mediated through the nervous system, the immune system, and hormones, and is known as the “microbiota-gut-brain axis.”
Studies with mice showed that probiotics improve learning and memory and reduce anxiety and depression- and obsessive-compulsive disorder-like symptoms. The evidence for these effects in humans, however, remained limited.
Here, a team of scientists at Kashan University of Medical Sciences in Iran and Islamic Azad University in Tehran, Iran, performed a randomized, double-blind, clinical trial with Alzheimer’s patients.
They recruited a total of 52 women and men between the ages of 60 and 95 with Alzheimer’s disease and tested the effects in patients’ cognition after treatment with probiotics.
Half the patients were randomly assigned to receive daily doses of 200 ml milk enriched in probiotics, specifically these bacteria species: Lactobacillus acidophilus, L. casei, L. fermentum, and Bifidobacterium bifidum. The other patients (the controls) received untreated milk.
The trial lasted for 12 weeks. Scientists conducted blood tests on all the participants at the beginning and the end of the trial. They also tested the cognitive function of the subjects with the Mini-Mental State Examination (MMSE) questionnaire.
Researchers observed that in the group of patients receiving probiotics, the average score on the MMSE questionnaire increased significantly, from 8.7 to 10.6. The maximum MMSE score is 30. But in the control group, there was little change; the average MMSE score went from 8.5 to 8.0.
The scientists acknowledged the increase was moderate and that patients remained severely impaired in cognition, but they noted that the results are important because they show that probiotics have an effect on human cognition, possibly improving it.
Future research is required to understand whether increasing the time of treatment with probiotics may lead to sustained and longer beneficial outcomes.
“In a previous study, we showed that probiotic treatment improves the impaired spatial learning and memory in diabetic rats, but this is the first time that probiotic supplementation has been shown to benefit cognition in cognitively impaired humans,” Kashan University Prof. Mahmoud Salami, the study’s lead author, said in a press release.
“These findings indicate that change in the metabolic adjustments might be a mechanism by which probiotics affect Alzheimer’s and possibly other neurological disorders,” Salami said. “We plan to look at these mechanisms in greater detail in our next study.”
Walter Lukiw, professor of neurology, neuroscience and ophthalmology and Bollinger Professor of Alzheimer’s disease at Louisiana State University, commented on the study.
“This early study is interesting and important because it provides evidence for gastrointestinal (GI) tract microbiome components playing a role in neurological function, and indicates that probiotics can in principle improve human cognition,” he said.
“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, and that both the GI tract and blood-brain barriers become significantly more leaky with aging, thus allowing GI tract microbial exudates (e.g. amyloids, lipopolysaccharides, endotoxins and small non-coding RNAs) to access central nervous system compartments,” Lukiw added.