Harvard study links gut bacteria to lower anxiety levels
Researchers at Harvard University have identified specific gut microbiome compositions associated with reduced anxiety in humans. The two-year study, published today, strengthens evidence for the gut-brain connection. This discovery opens doors to microbiome-based mental health interventions.
In a landmark investigation published on October 1, 2025, in the journal Science, a team led by Dr. Emily Carter at Harvard University examined the role of gut bacteria in mental health. The study tracked 500 participants over two years, analyzing their gut microbiomes through stool samples and correlating findings with self-reported anxiety levels via standardized psychological assessments.
The researchers discovered that individuals with higher abundances of certain bacterial strains, such as Lactobacillus and Bifidobacterium, exhibited significantly lower anxiety scores. "Our findings suggest that modulating the gut microbiome could be a novel therapeutic approach for mental health disorders," Dr. Carter stated in the paper's discussion section. This builds on prior animal studies that hinted at the gut-brain axis—a bidirectional communication pathway between the digestive system and the central nervous system—but marks the first large-scale human confirmation.
Participants were diverse in age, gender, and ethnicity, recruited from the Boston area starting in 2023. The study controlled for factors like diet, exercise, and medication use to isolate microbiome effects. Notably, those with balanced microbiomes showed up to 30% lower anxiety metrics compared to others.
Background context reveals growing interest in the microbiome's influence on behavior. Earlier research, such as 2019 rodent experiments, demonstrated how gut bacteria affect neurotransmitter production like serotonin, much of which originates in the gut. However, human data has been limited until now.
Implications are promising yet preliminary. The team calls for clinical trials testing probiotics or fecal transplants for anxiety treatment. While not a cure-all, this could complement existing therapies like cognitive behavioral therapy or antidepressants. Experts caution that causation isn't fully proven—correlation doesn't imply direct cause—but the robust sample size lends credibility.
This work underscores the microbiome's untapped potential in psychiatry, potentially shifting treatment paradigms toward holistic, biology-informed strategies.