Blueberry Study Explores Link Between Gut Health and Mood

Key Developments:

• Small trial links blueberry intake to changes in gut microbial genes
• Researchers found no significant mood difference versus placebo

(Science Daily) — October 19, 2026: Daily blueberry consumption may influence certain gut microbial functions in older adults, according to a preliminary study exploring the relationship between diet, intestinal bacteria and mood.

The research, published in The Journal of Nutrition, Health and Aging, examined whether compounds in blueberries could affect gut microbiome activity and depressive symptoms in adults aged 65 and older. Although participants who consumed blueberry powder showed a more consistent reduction in reported depressive symptoms, the improvement was not statistically significant compared with the placebo group.

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The researchers cautioned that the results do not establish blueberries as a treatment for depression. Instead, the findings provide an initial basis for investigating how specific foods may interact with gut microbes and processes associated with mental health.

Lead author Courtney L. Millar, a researcher at Hebrew SeniorLife’s Hinda and Arthur Marcus Institute for Aging Research and an assistant professor at Harvard Medical School and Beth Israel Deaconess Medical Center, explained the scientific rationale.

"Fiber and anthocyanins in blueberries have potential to modify the gut microbiome and metabolites that are relevant to depression in older adults," Millar said. She added: "Our objective was to preliminarily determine the effect of blueberry consumption on the gut microbiome, metabolites, and depressive symptoms."

The trial enrolled sedentary adults aged 65 or above who reported mild depressive symptoms. Participants were randomly assigned to receive either 48 grams of blueberry powder daily—equivalent to approximately two cups of fresh blueberries—or a placebo powder for three months. The study used a double-blind design, meaning participants and researchers were not informed of the assigned treatment during the trial.

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Only 18 participants completed the intervention: 10 in the blueberry group and eight in the placebo group. Most were women, and the participants were predominantly white. The small and relatively narrow sample limits how confidently the results can be applied to the wider older population.

Woman Holding Organic Blueberry Blueberries are small, nutrient-rich fruits packed with fiber, vitamins, and anthocyanins—the pigments responsible for their deep blue color. Credit: Shutterstock.

Researchers assessed participants’ gut bacteria and the genes associated with microbial activity through metagenomic sequencing. They also measured short-chain fatty acids in stool samples and used validated questionnaires to assess depressive symptoms before and after the intervention.

The analysis did not show meaningful overall changes in the abundance of bacterial species, broader microbial metabolic pathways or measured short-chain fatty acid metabolites. However, researchers detected changes in the abundance of genes associated with several microbial enzymes within the blueberry group.

One of the identified enzymes was Polyamine Transporting ATPase, classified as EC 3.6.3.31. The study linked this enzyme to a pathway involved in the production of gamma-aminobutyric acid, or GABA, a neurotransmitter involved in communication within the nervous system. The findings do not establish that blueberry consumption increased GABA levels in the brain or improved mental health through this pathway.

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The mood results were similarly inconclusive. Participants receiving blueberry powder appeared to experience a greater reduction in depressive-symptom scores, with less variation in their responses. However, the difference between the blueberry and placebo groups did not reach statistical significance. The study therefore cannot confirm that the fruit itself produced a measurable antidepressant effect.

Dr. Rafaela G. Feresin, associate professor in GSU’s Department of Nutrition, is leading cutting-edge research exploring how wild blueberry polyphenols may: Improve gut microbiota balance, Support heart & brain function, Offer benefits for prediabetes and hypertension. CREDIT: @gsunutrition/Instagram.

The findings raise questions about whether dietary compounds can alter particular microbial functions without substantially changing the overall composition of gut bacteria. Further research involving larger and more diverse groups will be needed to determine whether these changes are reproducible and whether they have any meaningful relationship with mood.

The study, titled A pilot study of daily blueberry intake modulates the gut microbiota enzyme commissions in older, sedentary adults with mild depressive symptoms, was published in The Journal of Nutrition, Health and Aging.

For now, the research offers an early insight into the possible relationship between blueberries, gut microbial activity and emotional wellbeing in older adults. It does not establish that eating blueberries every day prevents or treats depression, and the findings should not replace professional assessment or treatment for people experiencing persistent depressive symptoms.

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