Blueberries Shift Gut Bacteria in Older Adults

A small Harvard Medical School pilot study found blueberry powder changed gut bacteria enzymes in older adults, though depressive symptom improvements did not differ significantly from placebo.

Updated on Nov. 3, 2026 in Nutrition

Flat-color vector editorial illustration of a mound of blueberry powder spilling from a glass jar beside a glowing amber test tube. — Harvard Medical School researchers found daily blueberry powder shifted six gut bacteria enzyme genes in 18 older adults, though mood changes did not differ from placebo. AI Illustration. Upload story photo >

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Harvard Medical School researchers reported a pilot study of 18 adults aged 65 and older who took 48 grams of freeze-dried blueberry powder or placebo daily for three months. Six bacterial enzyme genes changed in abundance in the blueberry group, while depressive symptoms improved in both groups without a statistically significant difference between them.

Why it matters

The results suggest a possible link between blueberries, the gut microbiome and mood in older adults, a population where depression is common. Because the sample was small and the symptom difference was not significant, the findings are preliminary and do not establish a treatment effect.

The study enrolled 18 participants aged 65 and older over three months, with 48 grams of daily blueberry powder compared against placebo. Whether the observed microbial shifts translate to mood benefits remains unknown, as the sample size was too small to estimate statistical power.

The players

Harvard Medical School

A leading medical school of Harvard University in Boston, Massachusetts, widely known for biomedical research.

The details

Participants were randomly assigned to daily blueberry or placebo powder, and researchers measured gut microbiome composition, metabolites and depressive symptoms. One changed enzyme gene is involved in producing gamma-aminobutyric acid (GABA), a neurotransmitter linked to mood regulation, though the study was not designed to confirm that pathway. The findings were published in the Journal of Nutrition, Health and Aging.

Study duration: three months
Article published: November 3, 2026

Health Landscape

The study adds to a growing body of research on the gut-brain axis, in which gut bacteria and their metabolites are investigated as potential influences on mood. Its preliminary design means it extends that line of inquiry rather than establishing a clinical benefit.

For older adults, the results do not yet justify changing treatment or adding blueberries as a mood intervention. Readers interested in diet should note that the study used concentrated freeze-dried powder rather than whole fruit.

The takeaway

Blueberries may influence gut bacteria in older adults, but this small study cannot confirm any effect on mood. Larger trials will be needed to determine whether dietary changes meaningfully affect depression.