New research has found that gut bacteria and chemicals could be used to identify people with mild cognitive impairment and help predict how quickly their memory and thinking might decline.
In what is thought to be the first study of its kind, researchers from Cardiff University and Imperial College London examined both gut bacteria and chemicals. Their findings could support earlier diagnosis and help spot people at risk of faster decline.
This study leads us to conclude that the gut could offer a window into what's happening in the brain at the earliest stages of cognitive decline.
The researchers analysed faecal samples from 35 older adults, most of them couples living together where one partner had mild cognitive impairment and the other did not, and used machine learning to see whether the samples could help diagnose the condition and predict how quickly it progresses.
The study found that people with mild cognitive impairment had a different mix of gut bacteria compared to people without cognitive impairment. In particular, people with mild cognitive impairment displayed significantly elevated levels of the bacteria Izemoplasmatales spp. and the gut chemical proline. They also showed decreased levels of Ruminococcus spp. and Lachnospira spp. bacteria, and lower levels of the chemical fumaric acid.
These bacteria belong to a larger group that has been linked to brain health in previous studies.
The team also tested for these bacterial markers in an independent group of people from a previous study, where they could still distinguish people with mild cognitive impairment from healthy individuals.
The researchers followed people with mild cognitive impairment for a year. They found that those whose initial samples had higher levels of the bacteria Bilophila spp. and the chemicals arginine, aspartic acid and hypoxanthine, and lower levels of Coprococcus spp., showed a faster decline in memory and thinking skills.
Study co-author Dr You Zhou, Cardiff University, said: "Mild cognitive impairment affects around one in four older adults worldwide, but we have no simple way of telling who will go on to decline quickly."
We found that a combination of gut bacteria and chemicals could distinguish people with mild cognitive impairment from healthy individuals with high accuracy, and certain gut chemicals were strongly linked to faster decline over the following year.
"This was a small study and the findings need confirming in larger groups, but they point towards simple, non-invasive tests that could one day support earlier diagnosis."
Co-author Professor Julian Marchesi, Imperial College London, said: "Gut bacteria and chemicals are increasingly recognised as an important link between the gut and the brain. By looking at both together, we get a much fuller picture of what's changing in people with mild cognitive impairment. Future studies on larger groups of patients will help pinpoint exactly which microbes and chemicals matter most."
The researchers say further studies are now needed in more diverse groups and to examine the influence of diet, lifestyle, ethnicity, environment and genetic risk.
The research, Profiling Gut Microbiome and Metabolites Aids Diagnosis and Prediction of Progression in Mild Cognitive Impairment , was published in MedComm. The study was funded by the Rosetrees Trust. The researchers thank the participants and the Memory Team at Cardiff and Vale University Health Board.
