The bacteria in a child’s gut may play a bigger role in their future mental health than scientists once thought.
A new study from UCLA Health suggests that the makeup of a child’s gut microbiome at age 2 may help shape brain development in ways that influence emotional health years later. The findings, published in Nature Communications, add to growing evidence that gut microbes interact closely with the brain, potentially affecting risk for anxiety and depression.
Researchers found that toddlers whose gut microbiomes contained higher levels of bacteria from two groups — Clostridiales and Lachnospiraceae — were more likely to show symptoms of anxiety or depression, known as “internalizing” symptoms, in middle childhood. The link appeared to work indirectly: those early microbial patterns were associated with changes in brain network connectivity related to emotion and stress regulation.
“By linking early-life microbiome patterns with brain connectivity and later symptoms of anxiety and depression, our study provides early evidence that gut microbes could help shape mental health during the critical school-age years,” said senior author Dr. Bridget Callaghan, associate professor of psychology at UCLA and the Bernice Wenzel and Wendell Jeffrey Term Endowed Chair in Developmental Psychology.
The team drew on data from the Growing Up in Singapore Towards Healthy Outcomes (GUSTO) study, which has tracked children’s health from birth. The UCLA analysis included 55 participants with stool samples collected at age 2, brain scans at age 6 and caregiver reports of emotional and behavioral symptoms at age 7½.
Callaghan said the findings mirror patterns seen in adults, where certain microbes have been linked to stress response and depression. Some species within these microbial groups appear more sensitive to stress and may affect how the brain’s emotion networks develop.
Previous research on the gut–brain axis in children has focused mainly on early cognitive or motor development. This study is among the first to show how gut microbes might be connected to later emotional health, a period when conditions like anxiety and depression often first emerge.
While the study does not prove causation, Callaghan said it offers promising directions for future research.
“We need to figure out what species within these larger groups are driving the findings,” she said. “Once we have that information, there are relatively straightforward ways to change the microbiome, like probiotics or diet, that we could use to address issues.”
The researchers say understanding how early microbial patterns shape emotional development could open new possibilities for early interventions that support both mental and physical health as children grow.
The study was supported by multiple international agencies, including the Agency for Science, Technology and Research (A*STAR) in Singapore; the Singapore National Research Foundation; the UK Medical Research Council; the U.S. National Institutes of Health; and Alzheimer’s Research UK. Additional support came from the National Institute for Health and Care Research, the JPB Foundation’s Toxic Stress Network and UCLA’s Goodman-Luskin Microbiome Center.