With mounting evidence suggesting a gut link in Alzheimer’s Disease (AD), scientists have been keenly studying the use of probiotics to treat the neurogenerative condition. But so far, most of these studies have been in animal models.
Now, a small but promising trial from Japan suggests that probiotics could offer protection against declining memory in older adults.
Researchers from The University of Tokyo’s department of integrated biosciences and the Meiji Corporation (which manufactures food and dairy products) have trialled the probiotic intervention on adults showing early signs of AD.
Decades before the significant effects of AD are seen, mild memory loss is a symptom. Research shows that 90 per cent of the time, amnestic mild cognitive impairment (MCI) is associated with AD progression.
The new research follows earlier studies that tested nutritional interventions – including anserine, camosine and green tea extract – in which they found that nutritional and lifestyle changes could help tackle cognitive decline.
The latest trial utilised “microbiota-gut–brain axis-mediated dietary intervention”, with the goal of boosting gut health to reduce the symptoms or severity of AD progression. The bacteria of choice was a strain called Lactiplantibacillus plantarum [OLL2712] – commonly found in fermented foods.
Also read: New Alzheimer’s study zeroes in on a gut-brain genetic nexus
“After 12 weeks of supplementation… the intake group showed significant improvement in composite memory and visual memory, and a lower relative abundance of Lachnoclostridium, Monoglobus, and Oscillibacter, the genera involved in inflammation,” the researchers wrote.
This strain is known to have antimicrobial, antioxidative, antigenotoxic, anti-inflammatory and immunomodulatory properties.
The double-blind placebo-controlled trial included 78 participants, all over the age of 65, and living in the area around Kashiwa City in Japan’s Chiba Prefecture. At the start and end of the trial, the participants performed a word list memory test to gauge their memory.
One group received a probiotic and the other a placebo. Researchers also monitored the participants’ diet and collected fecal samples in the week before the follow-up test to check the diversity of gut bacteria.
Making a probiotic for AD
To make the probiotic, the researchers heat-treated the Lactiplantibacillus plantarum cells and cultured them in a medium containing by-products of skimmed milk powder. This was then dried to a powder and mixed with dextrin, a derivative of starch.
The researchers say consumption of the probiotic had a “protective effect on memory function in older adults”. But they found that while composite and visual memory appeared to improve, there was no improvement in verbal memory of the participants.
However, visual memory scores have shown to be a better predictor than verbal memory scores of whether a person will end up with MCI, and it is understood to be one of the “earliest symptoms of the AD spectrum”.
On the gut health front, the group that received the probiotic had lower concentrations of bacteria linked with inflammation.
“As there is currently no effective pharmacotherapy established to prevent the onset and progression of cognitive decline in the pre-dementia stage, the results suggest that continuous intake of OLL2712 may be an effective approach to protect memory function in older adults,” the researchers concluded in the paper.
More research needed
One of the study’s limitations is its small sample size. In the paper, the authors say a larger sample size would better establish the link between probiotics and memory since in this case even a small variation in score could appear as a significant improvement.
The study only included healthy volunteers and cannot be generalised to the entire elderly population. Moreover, it did not look at changes in the overall gut microbiota composition but in a single sample.
“We considered the analysis of the amount of change before and after the intervention to be not very effective in the analysis of gut microbiota because of the large intra-subject variability,” the researchers noted.
They added that to truly compare before-and-after results, they would need to extract and standardize fecal samples from each subject on three or more days. Nevertheless, this is the first randomised control trial to demonstrate the efficacy of the bacterial strain in improving memory function in older adults.
The gut promise for AD treatment
Gut microbiota may seem an unlikely factor for good memory. But many studies, mostly in animals, point to a tangible link.
Linking what we eat with how much we remember requires a greater understanding of the mechanism of memory. Certain probiotics have increasingly been associated with improving cognition and mental health, ranging largely from their effect on boosting neurotransmitter production.
When it comes to conditions like Alzheimer’s, reduced microbial diversity has been identified in studies, however, the exact link between probiotics and AD remains unclear. A multi-pronged approach is likelier than a single cure-all. But in the pursuit of futuristic therapies, every step counts.
