A UCLA Study Links Gut Bacteria to How Fast the Brain Ages

A new study from UCLA suggests that how fast the brain ages may be linked to bacteria in the gut and the chemicals they make. The results offer a new view of changes that may begin long before anyone notices problems with memory or thinking.

For years, scientists have used brain scans to estimate a person's "brain age," which can differ from their real age. Earlier research found that when a brain looks older than expected, it can be linked to poorer memory, weaker thinking skills and changes in mood. But most earlier studies looked at older adults or people with brain conditions. It was unclear whether an older-looking brain matters in younger, generally healthy adults.

In the new study, published in the journal eBioMedicine, UCLA Health researchers studied brain scans from nearly 1,500 adults split into three groups. The scans measure how different brain areas communicate with each other while a person is resting. The team built a computer model that estimated each person's age from those patterns. The difference between the estimated brain age and the actual age was called the Brain Aging Index, or BAI.

In all three groups, people whose brains looked older than their actual age generally did worse on tests of working memory and executive function. These abilities help people keep information in mind, stay focused, plan and organize. People with a higher index also reported more symptoms of depression. The patterns often involved brain regions linked to memory and to thinking about oneself.

For one group, the researchers also studied stool samples. Researchers discovered that a higher Brain Aging Index was linked to specific gut bacteria and various chemical leftovers, such as certain fat molecules, a substance related to cholesterol, and reduced amounts of a hormone known as estetrol. The related pathways involved the immune system, blood vessel function, communication between brain cells and how cells make energy.

Dr. Arpana Church, the senior author and co-director of the Goodman-Luskin Microbiome Center at UCLA Health, said brain aging does not suddenly begin when we get older, and its biological signals may be detectable decades earlier. By linking early brain changes with the gut microbiome and its byproducts, she said, scientists are starting to find pathways that might one day be targeted to prevent problems.