Blueberry study finds gut enzyme changes but no mood improvement
A three-month pilot study in older adults with mild depression found daily blueberry powder did not significantly improve mood more than a placebo.
A three-month pilot trial found no significant difference in depressive symptoms between older adults consuming daily blueberry powder and those taking a placebo. The randomized, double-blind study involved 18 physically inactive adults aged 65 and older who were experiencing mild depressive symptoms.
Participants were divided into two groups. One group consumed 48 grams of blueberry powder daily, equivalent to about two cups of fresh berries. The other took a matching placebo powder. Depressive symptoms were measured using validated questionnaires before and after the three-month intervention. The blueberry group showed a greater reduction in symptoms, but the difference was not statistically significant.
| Group | Number of Participants | Mean Age |
|---|---|---|
| Blueberry | 10 | 71 ± 4 |
| Placebo | 8 | 75 ± 6 |
Most participants were women and the group was predominantly white.
Blueberry group shows changes in gut microbial genes
Despite the lack of a clear mood benefit, the blueberry group exhibited statistically significant changes in genes related to gut microbial enzymes. Researchers used metagenomic sequencing to analyze the gut microbiome and liquid chromatography/mass spectrometry for metabolites.
The overall abundance of microbial species and short-chain fatty acid metabolites did not change. However, the abundance of genes for specific gut microbial enzymes shifted. One identified gene, EC 3.6.3.31 Polyamine Transporting ATPase, is involved in the production of GABA, a neurotransmitter crucial for brain signaling.
Researchers highlight gut-brain axis potential
The study authors suggest that compounds in blueberries may influence the gut microbiome in ways relevant to depression, even if clinical mood effects were not detected in this small trial. The research was published on October 18, 2026, in the Journal of Nutrition, Health and Aging.
Lead author Courtney L. Millar, PhD, an assistant scientist at Hebrew SeniorLife's Hinda and Arthur Marcus Institute for Aging Research, explained the goal. "Our objective was to preliminarily determine the effect of blueberry consumption on the gut microbiome, metabolites, and depressive symptoms," Millar said.
She noted that the fiber and anthocyanins in blueberries have the potential to modify the gut microbiome and metabolites relevant to depression in older adults. The connection between consumption and mental well-being is linked to the gut-brain axis, a communication pathway between the digestive system and the brain.
Other contributors included researchers from Harvard T.H. Chan School of Public Health, the Broad Institute, and the University of Connecticut. The study concludes that while blueberry intake did not significantly improve mood in this pilot, it modulates gut microbiota enzyme activity, warranting further investigation.
