Probiotics found in yoghurt and supplements could help improve the thinking and memory for people with Alzheimer’s disease, research has found.

In a clinical trial involving 52 people, those who drank a daily dose of lactobacillus and bifidobacterium bacteria for 12 weeks showed improvements on tests to measure cognitive impairment.

In contrast, those who were not given the probiotic supplements declined over the same period.

Researchers at from Kashan University of Medical Sciences, Kashan, and Islamic Azad University, in Tehran, Iran, say that it suggests altering gut bacteria could help people suffering from neurodegenerative conditions.

"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," says Professor Mahmoud Salami from Kashan University, the senior author of the study.

"These findings indicate that change in the metabolic adjustments might be a mechanism by which probiotics affect Alzheimer's and possibly other neurological disorders," says Salami. "We plan to look at these mechanisms in greater detail in our next study."

Probioticsare known to give partial protection against certain conditions such as irritable bowel syndrome, inflammatory bowel disease, eczema, allergies, colds, tooth decay, and periodontal disease.

But scientists have long hypothesized that probiotics might also boost cognition, as there is continuous two-way communication between the intestinal bacteria and the brain along the so-called "microbiota-gut-brain axis" which links the nervous system, the immune system, and hormones.

In mice, probiotics have been shown to improve learning and memory, and reduce anxiety and depression. But until not there has been no evidence of cognitive benefits in humans.

The researchers conducted a trial in which women and men with Alzheimer’s disease, aged between 60 and 95. Half of the patients daily received 200 ml milk enriched with four probiotic bacteria Lactobacillus acidophilus, L. casei, L. fermentum, and Bifidobacterium bifidum - approximately 400 billion bacteria per species -while the other half received untreated milk.

Many probiotic yoghurts and drinks, such as Yakult, contain the same bacteria although in smaller doses. Yakult, for example contains around 6.5 billion L. casei, while most supplements contain around 30 billion.

At the beginning and the end of the 12-week experimental period, the scientists tested the cognitive function of the subjects with Mini-Mental State Examination (MMSE) scale, a standard measure of cognitive impairment, which includes tasks like giving the current date, counting backwards from 100 by sevens, naming objects, repeating a phrase, and copying a picture.

Over the course of the study, the average score on the MMSE questionnaire significantly increased, from 8.7 to 10.6, out of a maximum of 30, in the group receiving probiotics, but not in the control group, where it fell from 8.5 to 8.0.

Even though this increase is moderate, and all patients remained severely cognitively impaired, the results are the first to show that probiotics can improve human cognition.

Walter Lukiw, Professor of Neurology, Neuroscience and Ophthalmology and Bollinger Professor of Alzheimer's disease at Louisiana State University, who reviewed the study but was not involved in the research, said: "This early study is interesting and important because it indicates that probiotics can in principle improve human cognition.

“This is in line with some of our recent studies which indicate that the gastrointestinal tract microbiome in Alzheimer's is significantly altered in composition when compared to age-matched controls.”

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