TL;DR
A UCLA-led study found that adults whose brains appeared older than their chronological age tended to score lower on working-memory and executive-function tests and report more depressive symptoms. In one of three groups, a higher brain-aging score was also associated with particular gut bacteria and metabolic compounds; the findings show links, not that gut microbes cause brain aging.
A UCLA Health study of nearly 1,500 adults found that people whose brains appeared older than their chronological age tended to perform worse on working-memory and executive-function tests and report more depressive symptoms. In one of the study’s three groups, a higher brain-aging score was also associated with specific gut bacteria and metabolic byproducts, suggesting a relationship researchers say warrants further study—not proof that gut microbes cause the brain to age.
The study, published in eBioMedicine, used resting brain scans to measure how different brain areas communicated. Researchers trained a computer model to estimate each participant’s age from those patterns, then compared that estimate with the person’s actual age. The difference was called the Brain Aging Index. A higher index meant the brain appeared older relative to the participant’s chronological age.
Across the three groups, participants with higher scores generally did worse on tests of working memory and executive function, abilities involved in holding information in mind, focusing, planning and organizing. They also reported more symptoms of depression. The researchers said the patterns repeatedly involved brain areas linked to memory and self-referential thought. These are group-level associations; the report does not establish that an individual score predicts a person’s future health.
For one group, the team also analyzed stool samples. A higher Brain Aging Index was associated with certain bacteria and several metabolic compounds, including some fat molecules, a cholesterol-related compound and lower levels of the hormone estetrol. The associated biological pathways included immune activity, blood-vessel function, communication between brain cells and cellular energy production. The gut analysis was limited to that study group, rather than all participants.
Early Brain-Age Signals and Gut Links
The findings add to research asking whether measurable differences in brain health can appear before memory or thinking problems are obvious. The study included adults beyond the older or neurologically ill populations often examined in earlier research, according to the report. Its results point to a possible connection between brain communication patterns, cognitive and mood measures, and gut biology in adults who may not yet have noticeable impairment.
That connection could guide future research into whether gut-related signals help identify people who may be more vulnerable to later cognitive or mood changes. But the study did not test a diet, supplement, probiotic or other intervention, and it does not show that changing gut bacteria can slow brain aging. The practical significance for readers is a research lead, not a current screening or treatment recommendation.
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How Researchers Estimated Brain Age
“Brain age” is an estimate derived from biological measurements, not a person’s actual age or a clinical diagnosis. In this study, the estimate came from patterns of communication between brain regions while participants were resting. Researchers compared that estimate with chronological age to create the Brain Aging Index.
Earlier research has associated brains that appear older than expected with poorer memory, weaker thinking skills and changes in mood, but much of that work focused on older people or those with neurological conditions, the ScienceDaily report said. The UCLA team examined three separate adult groups. Its findings extend the question to a broader set of adults, while the gut-microbe analysis applied to only one group. The report does not provide enough detail to treat the study as a test of cause and effect.
Association Does Not Show Cause
The reported results show associations, not causation. They do not establish whether gut bacteria or their byproducts affect brain aging, whether brain-related changes affect the gut, or whether other factors contribute to both. The report also does not establish that the observed bacterial or chemical signals can predict an individual’s future cognitive or mood health.
The stool-sample findings came from only one of the three groups. The source summary does not specify the group’s size, provide effect sizes or identify the bacteria and compounds by name. It is also unclear whether the links persist over time or apply across different populations. The findings do not amount to a validated diagnostic test, and the study did not test whether altering gut health changes brain-age estimates.
Further Studies Must Test the Links
The next step is to determine whether the reported relationships hold in larger and more varied groups and over time. Researchers would also need to test whether the gut-related signals precede changes in brain measures, and whether the associations remain after accounting for other influences on cognition, mood and the microbiome.
Church said the findings could help researchers explore earlier identification of people at risk and whether gut health might eventually be a target for strategies supporting brain health. Those possibilities remain prospective. Until intervention studies and further validation are available, the study offers no basis for using stool tests or changing diet or supplements specifically to alter a brain-aging score.
Key Questions
What did the UCLA study find?
Across three groups of adults, higher Brain Aging Index scores were generally associated with lower working-memory and executive-function test performance and more reported depressive symptoms. In one group, higher scores were also associated with particular gut bacteria and metabolic compounds.
Does the study show that gut bacteria cause brain aging?
No. The reported findings are associations and do not establish which factors cause the others, or whether another factor explains the links.
How did researchers estimate brain age?
They used a computer model to estimate age from resting brain scans measuring communication patterns between brain regions. They compared that estimate with each participant’s chronological age; the difference was the Brain Aging Index.
Can people use gut tests or supplements based on these results?
The study did not validate a gut test for predicting brain aging or test supplements, diet changes or other interventions. It does not support changing treatment or taking supplements on its own; people with health concerns should seek guidance from a qualified health professional.
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