Cheap and readily available fibre supplements could improve cognition among older adults, a major new study from King’s College London (KCL) has suggested. The results, published in Nature Communications, showed that people over 60 who took a daily prebiotic supplement for 3 months performed better in tests of memory and cognition than those taking a placebo.

The prebiotic group had significantly fewer errors on the paired associates learning test, a memory test focused on visual memory and new learning. This has clinical significance, the researchers said, as the test is used as an early identifier of Alzheimer’s dementia. Prebiotics may hold a key to preventing cognitive decline among ageing populations, they suggested.

What Do We Know About the Gut-Brain Connection?

Recent research shows that benefits of dietary fibre extend well beyond maintaining colonic health. 

Research also shows that some neurobiological processes underlying emotional, cognitive, and behavioural functions seem to be regulated by the microbiome: the collection of bacteria and other microorganisms residing in the gut.

A review from the University of Cork in 2019 noted two-way communication between the microbiota and the brain via multiple pathways, including the immune system, tryptophan metabolism, the vagus nerve, and the enteric nervous system. Microbiota have been implicated in neuropsychiatric conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease.

Impact of Pro- and Prebiotics on Cognition

Probiotics – supplements of live bacteria that directly modulate the composition of the microbiome – offer the potential to enhance cognitive function. In April last year, a review from the UK and Indonesia published in Neurological Sciences found that in 9 of 10 studies included, probiotic supplementation significantly improved cognitive function compared with control groups. A 2021 review from the University of Reading concluded that probiotics hold the potential to attenuate cognitive decline. 

Prebiotics, food components that include certain dietary fibres, are utilised by the microbiome, and thus indirectly modulate it. A 2019 review from the University of Louvain in Belgium found multiple intervention studies suggesting that prebiotics modulate human cognition and affect, including improvements in verbal episodic memory compared with placebo.

Memory and Learning Test Errors Halved on Prebiotics

For the new study, the KCL team conducted a double blind randomised trial among participants in its adult twin registry, pairing 36 individuals aged ≥60 (average 73, 78% female) randomised to receive a daily prebiotic supplement (inulin and fructo-oligosaccharides) for 12 weeks with their twin receiving a placebo. 

Results showed the cognitive score was significantly better in the prebiotic group, who had half the number of errors as the placebo group on the paired associates learning test. 

Lead researcher, Dr Mary Ni Lochlainn, a post-doctoral researcher and specialist registrar in geriatric and general internal medicine at KCL, explained to Medscape News UK that, although prebiotic fibre can be obtained from some fruits and vegetables, for trial purposes they needed a supplement with an exact dose to provide a standardised amount for each participant. 

In addition, while it’s generally preferable to increase dietary nutrients rather than take supplements, it can be difficult to change people’s diets. Older people in particular, she explained, often eat less due to a reduced appetite, poor dental health, socioeconomic reasons, and eating alone. So, for many older people, a supplement may be more feasible than dietary change. As the supplements used in the trial cost around 15 p/day, prebiotic intake can be increased for reasonably small costs. 

The team’s faecal analysis confirmed significant differences in microbiota composition, mostly driven by higher relative abundance of Bifidobacterium in the prebiotic group. 

Ni Lochlainn explained that a probiotic containing Bifidobacteria should have similar benefits, but there were additional challenges with probiotics, including the need for formulations that protect bacteria from being killed by stomach acid. Also, while prebiotics and probiotics are generally well tolerated, there are slightly increased risks of various rare side effects with probiotics. Additionally, prebiotics are usually cheaper, she added.

Prebiotics May Be Beneficial in Acute Settings

Ni Lochlainn’s team plans to carry out larger trials with longer timeframes to assess whether cognitive improvements from prebiotics are sustained. They also aim to test whether prebiotic supplements can benefit memory and thinking in acute settings, for example older people in hospital, she said.

Pending larger confirmatory studies, “increasing prebiotic-containing foods, or taking a commercially available prebiotic supplement, is a low risk option, which may well be useful” for individuals who are interested in cognitive protection, she said. 

“Important Study” Shows Positive Influence on Cognition

Glen Gibson, professor of food microbiology at the University of Reading, is credited with introducing the concept of a prebiotic in 1995. His research since has demonstrated the benefits of prebiotics on inflammatory markers, metabolic syndrome, irritable bowel syndrome, travellers’ diarrhoea, and most recently autism.

Asked to comment on the KCL study for Medscape News UK he said: “This is a very well-designed and reported study that addresses health parameters of gut microbiota modulation. The prebiotic nature of the intervention is confirmed through sophisticated analyses of the microbiome. Concomitant with this was a positive influence on cognitive function, which is a critical observation.” 

Because gut microbiota-mediated influences were seen in terms of cognitive aspects, “this is a very important study”, he added, and “another great output from the world class twins cohort research at KCL”.