Daily consumption of blueberry powder led to statistically significant changes in gut microbial enzymes in older, sedentary adults with mild depressive symptoms during a three-month pilot study, according to research led by Dr. Courtney L. Millar from Hebrew SeniorLife's Hinda and Arthur Marcus Institute for Aging Research. The study, involving 18 participants, indicated a possible connection between blueberries, the gut microbiome, and mood, despite direct mood benefits not reaching statistical significance.

This finding is important because it offers preliminary evidence of how diet might influence gut health and potentially impact neurological functions related to mood in older populations. Understanding these mechanisms could pave the way for future dietary interventions aimed at supporting mental well-being as people age.

What the Records Show

The study, published in the Journal of Nutrition, Health and Aging, was a randomized, double-blind, parallel-arm, placebo-controlled trial over three months. Eighteen sedentary adults, aged 65 and older, experiencing mild depressive symptoms participated. The active group of 10 individuals consumed 48 grams of blueberry powder daily, equivalent to about two cups of fresh berries, while a placebo group of 8 received a matched powder.

While participants in the blueberry group showed a greater and more consistent reduction in depressive symptoms, this difference was not statistically significant compared to the placebo group. However, the study observed statistically significant changes in the gene abundance of several enzyme commissions within the gut microbiome of the blueberry group. Specifically, changes were detected in EC 3.6.3.31 Polyamine Transporting ATPase, an enzyme involved in the production of the neurotransmitter gamma-aminobutyric acid (GABA). The research was supported by the National Institute on Aging, part of the National Institutes of Health.

Timeline

Hebrew SeniorLife issued a press release about the study on September 3, 2026. News articles detailing the findings appeared on ScienceDaily on October 18, 2026, and Scitechdaily on October 15, 2026. An Instagram post from Hebrew SeniorLife discussing the pilot study also appeared on July 9, 2026.

What Changed and For Whom

The study revealed subtle shifts in microbial genes within the gut microbiome of the older adults who consumed blueberries daily. These changes suggest that blueberries may have a direct impact on the enzymatic activities of gut bacteria. The target population for these potential changes were sedentary adults aged 65 and older who exhibited mild depressive symptoms. The consistent reduction in depressive symptoms observed in the blueberry group, though not statistically significant, points to a potential, yet unconfirmed, benefit for this demographic.

What the Subject Has Said Publicly

Dr. Courtney L. Millar, lead author of the study, assistant scientist II at Hebrew SeniorLife's Hinda and Arthur Marcus Institute for Aging Research, and assistant professor of medicine at Beth Israel Deaconess Medical Center and Harvard Medical School, commented on the findings. Millar stated, "Fiber and anthocyanins in blueberries have potential to modify the gut microbiome and metabolites that are relevant to depression in older adults". She added that the study's objective was to preliminarily determine how blueberry consumption affects the gut microbiome, metabolites, and depressive symptoms. Millar noted that the preliminary data from the study warrants additional research into this gut-brain connection.

What we could not confirm

Whether daily blueberry consumption directly leads to statistically significant improvements in mood or depressive symptoms in older adults was not confirmed by this pilot study. The long-term effects of these observed gut microbial enzyme changes on overall health and mood were also not established. The specific mechanisms through which changes in EC 3.6.3.31 Polyamine Transporting ATPase might influence GABA production and subsequent mood were not fully elucidated.