A small study of older adults has found that daily blueberry powder may influence some gut microbial functions, but it did not show a statistically significant improvement in depressive symptoms compared with a placebo.
The findings offer preliminary evidence for further investigation of diet, gut microbes and mood—not proof that blueberries can treat or prevent depression.
The research, published in the Journal of Nutrition, Health and Aging, examined sedentary adults aged 65 and older with mild depressive symptoms. It has drawn renewed attention through lifestyle coverage, including a Metro Mode report asking whether daily blueberries could ease low mood in older people.
What researchers tested
Participants were randomly assigned to consume 48 grams of blueberry powder each day, approximately equivalent to two cups of fresh berries, or a matched placebo powder for three months. The trial was double-blind, meaning neither participants nor the researchers conducting the intervention knew which powder each participant received.
The reported microbiome analysis included 18 participants: 10 in the blueberry group and eight in the placebo group. Most were white women, limiting how broadly the results can be applied.
Researchers assessed depressive symptoms with validated questionnaires and analysed stool samples to examine microbial species, genes and metabolites. The published study describes the work as a pilot investigation intended to test feasibility and provide preliminary data for a larger trial.
Mood improved in both groups
Measures of mental well-being improved over time in both groups. The reduction in depressive symptoms appeared larger and less variable among participants taking blueberry powder, but the difference between groups was not statistically significant.
That distinction is central to interpreting the findings. Improvement during a trial does not by itself demonstrate that the tested food caused it. The placebo comparison did not establish a blueberry-specific benefit for depressive symptoms.
A small trial can miss a real effect, but that possibility is not evidence that an effect exists. Larger studies are needed to determine whether any clinically meaningful mood benefit can be reproduced.
Subtle gut changes, not a proven gut-brain treatment
The blueberry group showed changes in the abundance of genes associated with several gut microbial enzymes. However, overall microbial species abundance, the measured metabolic pathways and short-chain fatty acid metabolites did not change.
These results suggest that particular microbial functions may respond to the intervention even without broad changes in the composition of the gut microbiome. They do not establish that the enzyme-related changes caused an improvement in mood.
The authors called for additional research into the relationship between blueberries, the gut microbiome and depressive symptoms in older adults. Their study does not support replacing professional assessment or established depression treatment with blueberries or supplements.
