The brain changes as people grow older, but those changes may begin long before noticeable signs of aging appear.

A new study from the University of California, Los Angeles, found that certain types of gut bacteria and the chemicals that they produce are associated with faster brain aging, which raises questions about how digestive health may influence memory, concentration and mood.

Researchers examined brain scans from nearly 1,500 adults across three separate groups. The study, published in the journal eBioMedicine, investigated whether biological signs of brain aging could be detected in generally healthy adults, rather than only in older people or individuals with neurological conditions.

To estimate brain age, researchers used brain scans to measure how different regions communicated with one another while participants rested.

Then, they developed a computer model to estimate each person’s brain age based on these communication patterns.

By comparing this estimate with each participant’s actual age, researchers calculated a Brain Aging Index that indicated whether someone’s brain appeared older or younger than expected.

The results showed that participants with higher Brain Aging Index scores generally performed worse on tests of working memory and executive function.

These abilities help people retain information, concentrate, plan and organize tasks.

Participants with higher scores also reported more symptoms of depression, suggesting that faster brain aging may be associated with changes in both cognitive performance and emotional well-being.

Researchers also examined stool samples from one group of participants to investigate possible connections between brain aging and the gut microbiome— the community of microorganisms living in the digestive system.

They found that higher Brain Aging Index scores were associated with specific gut bacteria and several metabolic byproducts, including certain fat molecules, a cholesterol-related compound and lower levels of a hormone called estetrol.

These biological signals were linked to processes involving the immune system, blood vessel function, communication between brain cells and cellular energy production.

Although the findings reveal connections between gut biology and brain aging, they do not establish that particular bacteria directly cause the brain to age faster.

“Brain aging doesn’t suddenly begin when we get older, but the biological signals may be detectable decades earlier,” Dr. Arpana Church, the study’s senior author and co-director of the Goodman-Luskin Microbiome Center at UCLA Health, said.

The findings could eventually help researchers identify individuals at risk of cognitive decline earlier in life. They also raise the possibility that improving gut health may become part of future strategies for supporting brain health.

However, additional research is needed to determine whether changing the gut microbiome can slow brain aging or improve memory and mood.

The study offers new insight into the relationship between the digestive system and the brain.

By connecting gut bacteria and their chemical byproducts with biological measures of brain aging, researchers have identified potential pathways for future investigation.

Further studies may help determine whether the gut microbiome can become a useful target for protecting cognitive health as people age.