However, the improvement in depressive symptoms was not statistically significant compared with the placebo group. The findings do not prove that blueberries reduce depression, but they offer preliminary clues about a possible connection between blueberry consumption, the gut microbiome and mental health.

“The fiber and anthocyanins in blueberries have the potential to alter the gut microbiome and metabolites associated with depression in older adults,” said lead author Courtney L. Miller, Ph.D., a scientific assistant at Hebrew Senior Life’s Hinda Arthur Marcus Institute on Aging and an assistant professor at Beth Israel Deaconess Medical Center and Harvard Medical School. “Our aim was to preliminarily investigate the effects of blueberry consumption on the gut microbiome, metabolites and depressive symptoms.”

How the blueberry study was conducted

Researchers recruited adults aged 65 and older who were physically inactive and experiencing mild depressive symptoms. The pilot study used a randomized, double-blind, parallel-arm, placebo-controlled design to examine whether daily blueberry consumption affected gut bacteria and mood.

Participants consumed either 48 grams of blueberry powder—approximately equal to 2 cups of fresh blueberries—or a matching placebo powder every day for three months.

Researchers used metagenomic sequencing to examine the participants’ gut microbiomes and measure the abundance of microbial species and genes. They also used liquid chromatography/mass spectrometry to analyze gut-derived fecal short-chain fatty acids, which are compounds produced by microbial activity.

Depressive symptoms were assessed with a validated questionnaire administered before and after the three-month intervention.

Blueberries were linked to subtle changes in gut microbial activity

A total of 18 participants completed the study. Most participants were women, and the groups were predominantly Caucasian. The placebo group included eight participants with a mean age of 75 ± 6 years, while the blueberry group included 10 participants with a mean age of 71 ± 4 years.

Although participants who consumed blueberries showed an encouraging pattern of reduced depressive symptoms, researchers found no statistically significant difference in mood improvement between the blueberry and placebo groups.

The gut microbiome results were also complex. The overall abundance of microbial species, MetaCyc metabolic pathways and short-chain fatty acid metabolites did not change significantly.

However, researchers identified statistically significant changes in the abundance of genes associated with several gut microbial enzymes among participants in the blueberry group. One was EC 3.6.3.31 Polyamine transport ATPase, which is involved in the production of gamma-aminobutyric acid, or GABA—a neurotransmitter that plays a role in brain signaling.

These findings suggest that blueberries may influence specific aspects of gut microbial function without producing measurable changes in the overall composition of the microbiome. Larger studies are needed to determine whether these changes can lead to significant improvements in mood or depressive symptoms.

What the findings mean

The study offers early evidence that daily blueberry consumption may affect gut microbial activity in older adults with mild depressive symptoms. However, because the study included only 18 participants and did not find a statistically significant difference in mood outcomes, the results should be considered preliminary.

The study was published as “A pilot study of daily blueberry consumption modulates enzyme activity in the gut microbiome in sedentary older adults with mild depressive symptoms” in the Journal of Nutrition, Health and Aging.

Other contributors included Deanna Sidney Walk, MD, of Hebrew Senior Life’s Memory Health Center, and Mohit P. Chopra, MD, of the Department of Psychiatry at Massachusetts Chan College of Medicine; Xochitl Morgan, Ph.D., and Emily A. Green, Ph.D., of the Department of Biostatistics at the Harvard T.H. Chan School of Public Health; Alex Wolff of Hebrew Senior Life’s Hinda and Arthur Marcus Institute on Aging; Kelly A. Pierce of the Broad Institute of MIT and Harvard University; and Lidan Gao, Ph.D., and Christopher N. Bledso, Ph.D., of the University of Connecticut’s Department of Nutritional Sciences.

Additional contributors included Alyssa B. Dufour, Ph.D., of Hebrew Senior Life’s Hinda and Arthur Marcus Institute on Aging, Beth Israel Deaconess Medical Center and Harvard Medical School; Douglas P. Keel, MD, MPH, of the Hinda and Arthur Marcus Institute on Aging at Hebrew Senior Life, Harvard Medical School and Beth Israel Deaconess Medical Center; and Louis A. Lipsitz, MD, of Hebrew Senior Life’s Hinda and Arthur Marcus Institute on Aging and Harvard Medical School.