Longevity Briefs: Can Probiotics Really Slow Brain Ageing?

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Within the human gut lives a collection of microorganisms referred to as the gut microbiome. These microorganisms play a role in digestion, metabolism, and overall health. As we age, the composition of the gut microbiome changes for the worse, which seems to contribute to many age-related diseases. For example, it can make the lining of the gut more ‘leaky’, allowing substances such as bacteria and toxins to pass through the gut lining and enter the bloodstream. This triggers chronic inflammation throughout the body, which is a known driver of many age-related disease including neurodegenerative diseases.

Studies suggest that the ageing gut microbiome can be restored to a youthful state fairly easily, and that this could be a strategy for slowing down the ageing process. For example, studies have found that transplanting gut microbiomes from young mice into old mice appears to reverse some aspects of brain ageing. Some companies have picked up on this research, and have begun to advertise probiotic treatments (delivering beneficial bacteria to the gut orally, such as in a capsule or powder) as a way to slow brain ageing in humans. Is there really enough evidence to back up these claims?

What did the researchers do: In this paper, researchers carried out a ‘mini-review’ of our current understanding of how the gut microbiome affects brain health. They then looked at the clinical evidence for whether probiotics could improve cognitive function in old age and in two diseases: Alzheimer’s disease and mild cognitive impairment (MCI).

Key takeaway(s) from this research: There is a strong association between poor gut microbiome health, increased chronic inflammation and an age-related decline in cognitive function in humans. Though we cannot be certain that this is a causal relationship, there are some compelling mechanisms through which gut bacteria could affect brain health, mainly by influencing levels of inflammation in the brain.

Despite the buzz around probiotics in both scientific reviews and lay media outlets, the researchers found only 9 clinical trials to be worthy of review. Two trials looked at the effects of probiotics in healthy over-65s, and while one trial found an increase in ‘mental flexibility’ in those taking probiotics compared to a placebo treatment, the other found no significant difference in cognitive performance. Four trials looked at patients with MCI and had generally encouraging results, with all studies showing some improvement in cognitive function and memory in those taking probiotics. Finally, 2 out of 3 studies recruiting patients with Alzheimer’s disease found improvements in cognitive function in those taking probiotics, though one of these studies is still under review.

So, while there is some evidence that probiotics can improve cognitive function in older adults, especially those with MCI, the evidence is not as strong as the excitement for these treatments might suggest. The largest study reviewed had a treatment group of 77 people, and studies used a variety of different bacterial strains. We should remain cautiously optimistic until larger, more comprehensive trials emerge.