Gut microbes linked to accelerated brain ageing in younger adults

The biological processes associated with brain ageing may begin far earlier than previously recognised, according to new research from UCLA Health that links accelerated brain ageing to specific gut microbes and the chemicals they produce. The study, published in the journal eBioMedicine, found that adults whose brains appeared biologically older than expected for their age showed poorer performance on tests of memory and executive function and reported more symptoms of depression. Researchers also identified distinct patterns in the gut microbiome associated with these accelerated ageing signatures.

The findings are significant because they suggest measurable changes linked to cognitive decline may be detectable decades before the appearance of obvious symptoms, potentially opening the door to earlier interventions aimed at preserving brain health. “Brain aging doesn’t suddenly begin when we get older, but the biological signals may be detectable decades earlier,” said Dr Arpana Church, co-director of UCLA Health’s Goodman-Luskin Microbiome Center and senior author of the study.

The research appears in the paper, Brain-gut crosstalk associated with brain ageing in young and mid-life adults: a multicohort cross-sectional study, published in eBioMedicine. This builds upon earlier inquires into the structural imaging measures of brain aging. Here, scientists have increasingly turned to advanced brain imaging to estimate “brain age”, a measure of how old the brain appears biologically rather than chronologically.

Previous investigations have shown that people whose brains appear older than expected often experience poorer cognitive outcomes and face increased risks of neurological disorders. However, most studies have focused on older populations or patients already living with neurological disease. The UCLA team instead examined whether these biological ageing patterns could be detected in younger adults who were largely healthy and symptom-free.

To investigate, researchers analysed brain scans from nearly 1,500 adults across three independent study cohorts. Using resting-state functional magnetic resonance imaging (fMRI), they measured communication patterns between different brain regions while participants were not engaged in specific tasks. The researchers then developed a machine-learning model capable of predicting age from those neural communication patterns. By comparing predicted age with actual age, they calculated a measurement called the Brain Aging Index (BAI). It was established that a higher score indicated that an individual’s brain appeared older than expected.

Across all three cohorts, a consistent pattern emerged. Participants with elevated Brain Aging Index scores performed less well on assessments of working memory and executive function. These cognitive abilities are essential for everyday tasks, helping individuals hold information temporarily in mind, concentrate on goals, make decisions, plan activities and organise complex tasks.

The association was not limited to cognitive performance, for people with older-appearing brains also reported higher levels of depressive symptoms, suggesting that accelerated brain ageing may influence mood as well as cognition. Notably, the researchers found repeated involvement of brain networks associated with memory processing and self-referential thinking, the mental processes involved in reflecting on one’s experiences, identity and emotions. The consistency of these findings across multiple populations strengthens the evidence that brain-ageing signals can be detected well before any clinical diagnosis of cognitive impairment.

The gut microbiome emerges as a key factor

The study’s most intriguing discovery came from analysis of the gut microbiome. In one participant cohort, researchers examined stool samples to determine whether brain ageing patterns correlated with differences in the microorganisms living within the digestive tract. They found that individuals with a higher Brain Aging Index possessed distinct gut microbial signatures. Accelerated brain ageing was also associated with several metabolic compounds, including specific lipid molecules, a cholesterol-related metabolite and lower levels of the naturally occurring hormone estetrol.

These biological signals converged on pathways involved in immune regulation, blood-vessel function, communication between brain cells and cellular energy production, all processes widely recognised as important components of healthy ageing. While the study does not prove that gut microorganisms directly cause accelerated brain ageing, it adds to a rapidly growing body of evidence showing that the gut and brain are closely connected through what scientists call the gut-brain axis.

The concept that microorganisms in the gut might influence brain health has gained significant scientific attention during the past decade. Research has linked microbial imbalances to conditions including Alzheimer’s disease, Parkinson’s disease, depression and anxiety. However, many earlier studies examined patients after symptoms had already emerged. The UCLA findings are notable because they push the timeline much earlier. Rather than focusing on disease, the researchers identified biological markers associated with accelerated ageing in adults who were still relatively young and generally healthy. This raises the possibility that the earliest stages of brain decline may be observable long before people experience noticeable memory problems or cognitive difficulties. Such a shift in understanding could have major implications for preventive medicine.

If future studies confirm that changes in the gut microbiome contribute to brain ageing, researchers may eventually be able to identify high-risk individuals earlier and develop targeted interventions to slow the process. Potential approaches could include dietary modification, microbiome-directed therapies or other strategies designed to influence the metabolic pathways identified in the study.

From treatment to prevention

The research reflects a broader trend in neuroscience towards detecting risk factors before disease develops. Many neurodegenerative conditions evolve slowly over decades. By the time symptoms become apparent, substantial biological changes may already have occurred within the brain. The ability to identify accelerated brain ageing earlier could therefore provide a valuable opportunity to intervene while the brain retains greater capacity for resilience and adaptation.

Church believes the findings represent an important step in that direction. “By linking these early brain changes with the gut microbiome and its metabolites, we are beginning to identify pathways that could ultimately help us understand who may be at risk and, importantly, where we might intervene to support healthier brain aging,” she said. For now, the study remains observational and cannot establish cause and effect. Nevertheless, by connecting brain-ageing signatures, cognitive performance and the gut microbiome in younger adults, the research offers fresh evidence that the roots of age-related decline may take hold far earlier than previously appreciated and that some of the answers may lie not in the brain itself, but in the trillions of microbes living within the gut.