A research team from Iran are the first to show how a daily dose of probiotics for 3 months could be effective for improving memory and thinking abilities in individuals with Alzheimer's disease.
The researchers found that Alzheimer's patients who consumed milk enriched with beneficial live bacteria every day for 12 weeks showed significant improvements in cognitive functioning.
Senior study author Prof. Mahmoud Salami, from Kashan University in Iran, and colleagues recently published their findings in the journal Frontiers in Aging Neuroscience.
Probiotics are defined as live microorganisms that are "helpful" to human health. These include bacterial groups such as Lactobacillus and Bifidobacterium, as well as yeasts, including Saccharomyces boulardii.
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Research has shown that these friendly microorganisms - many of which are added to food products, topical medications, and dietary supplements - may help protect against numerous infections and diseases, including irritable bowel syndrome (IBS), eczema, certain allergies, colds, and tooth decay.
Previous animal studies have also shown probiotics to improve learning and memory - an association that has been attributed to beneficial alterations in the gut microbiome that affect the brain. Whether probiotics have the same effect in humans, however, has been unclear.
Cognitive functioning scores improved with probiotics
For this latest study, Prof. Salami and team set out to determine the effects of probiotics on the cognitive functioning of 52 men and women aged 60-95 who had been diagnosed with Alzheimer's disease.
Participants were randomized to one of two groups. One group was required to drink 200 milliliters of normal milk every day for 12 weeks, while the other group drank 200 milliliters of milk containing four probiotic bacteria: Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus fermentum, and Bifidobacterium bifidum.
- More than 5 million adults in the United States are living with Alzheimer's
- Every 66 seconds, someone in the U.S. develops the disease
- Alzheimer's kills more people than breast cancer and prostate cancer combined.
Before and after the 12-week study period, researchers collected blood samples from the participants, and the subjects' cognitive functioning was assessed using the Mini-Mental State Examination (MMSE) scale.
As part of this examination, subjects are required to complete a number of tasks that test learning and memory, such as naming objects, counting backward, and copying a picture.
Compared with participants who consumed the untreated milk, those who received the probiotic-enriched milk demonstrated significant improvements in cognitive functioning, the team reports.
Subjects who consumed the treated milk saw average MMSE scores increase from 8.7 to 10.6 (out of a possible 30) during the 12-week study period, while scores dropped from 8.5 to 8.0 for those who drank the untreated milk.
The researchers stress that all participants remained severely cognitively impaired, but their findings are the first to show that probiotics might lead to some cognitive improvements.
"In a previous study, we showed that probiotic treatment improves the impaired spatial learning and memory in diabetic rats," notes Prof. Salami, "but this is the first time that probiotic supplementation has been shown to benefit cognition in cognitively impaired humans."
Cognitive benefits of probiotics may be down to metabolic changes
On assessing the participants' blood samples, the researchers found that subjects who consumed probiotics had lower triglycerides levels, lower levels of "bad" very low-density lipoprotein (VLDL) cholesterol, and reduced high-sensitivity C-reactive protein - a marker of inflammation.
Additionally, participants who received probiotics showed a reduction in two measures of insulin resistance and the functioning of insulin-producing beta cells in the pancreas - HOMA-IR and HOMA-B.
The team says these findings indicate the cognitive benefits of probiotics may be down to the metabolic changes they provoke. "We plan to look at these mechanisms in greater detail in our next study," notes Prof. Salami.
Walter Lukiw, a professor at Louisiana State University who was not involved in the study, hails the team's findings as "interesting and important," noting that they provide further evidence of a link between the gut microbiome and cognitive functioning.
"This is in line with some of our recent studies which indicate that the GI [gastrointestinal] 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," he adds.