However, the improvements in depressive symptoms were not statistically significant when compared with the placebo group. Although the findings do not establish that blueberries can relieve depression, they offer preliminary clues about a possible connection between blueberry consumption, the gut microbiome, and mental health.

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

Testing the Effects of Daily Blueberry Consumption

To investigate the potential connection, 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 evaluate whether consuming blueberries could influence gut microbes and mood.

Over three months, participants consumed either 48 grams of blueberry powder each day (approximately two cups of fresh berries) or a matching placebo powder.

Researchers examined the participants' gut microbiomes using metagenomic sequencing, which allowed them to measure the abundance of different microbial species and genes. They also used liquid chromatography/mass spectrometry to analyze gut-derived fecal short-chain fatty acids, compounds produced through microbial activity. Depressive symptoms were assessed using validated questionnaires administered before and after the three-month intervention.

Blueberries Linked to Subtle Changes in Gut Microbial Activity

A total of 18 participants completed the study. Most were women, and the group was predominantly white (placebo group, n = 8; mean age: 75 ± 6; blueberry group, n = 10; mean age: 71 ± 4).

Despite the encouraging pattern in depressive symptoms among participants consuming blueberries, the researchers found no statistically significant difference in mood improvements between the blueberry and placebo groups.

The gut microbiome results also revealed a mixed picture. The overall abundance of microbial species, MetaCyc metabolic pathways, and short-chain fatty acid metabolites remained unchanged.

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

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

The study, "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.

Other contributors included Mohit P. Chopra, MD, of the Deanna and Sidney Wolk Center for Memory Health at Hebrew SeniorLife and the Department of Psychiatry at UMass Chan Medical School; Xochitl Morgan, PhD, and Emily A. Green, PhD, of the Department of Biostatistics at Harvard T.H. Chan School of Public Health; Alex Wolfe of the Hinda and Arthur Marcus Institute for Aging Research at Hebrew SeniorLife; Kerry A. Pierce of the Broad Institute of MIT and Harvard; and Lidan Gao, PhD, and Christopher N. Blesso, PhD, of the Department of Nutritional Sciences at the University of Connecticut.

Additional contributors were Alyssa B. Dufour, PhD, of the Hinda and Arthur Marcus Institute for Aging Research at Hebrew SeniorLife and the Department of Medicine at Beth Israel Deaconess Medical Center and Harvard Medical School; Douglas P. Kiel, MD, MPH, of the Hinda and Arthur Marcus Institute for Aging Research at Hebrew SeniorLife, Harvard Medical School, and Beth Israel Deaconess Medical Center; and Lewis A. Lipsitz, MD, of the Hinda and Arthur Marcus Institute for Aging Research at Hebrew SeniorLife and professor of medicine at Harvard Medical School.