Small blueberry pilot finds no significant difference in depressive symptoms

Researchers conducted a randomized, double-blind, placebo-controlled pilot study in physically inactive adults aged 65 and older who had mild depressive symptoms. Participants received either 48 g of blueberry powder daily—described as equivalent to about two cups of fresh blueberries—or a matching placebo for three months. Eighteen participants completed the study: 10 in the blueberry group and eight in the placebo group. The researchers assessed depressive symptoms and analyzed stool samples for microbiome composition, microbial genes and short-chain fatty acids.

Symptoms declined more consistently among participants assigned blueberries, but the mood improvement was not statistically significant compared with placebo. Overall microbial species abundance, metabolic pathways and short-chain fatty acid levels also did not change. Within the blueberry group, researchers did find significant changes in the abundance of genes associated with several microbial enzymes, including one related to polyamine transport.

The findings are preliminary and do not establish that blueberries improve depression or that the observed microbial gene changes explain mood effects. The small sample and lack of a significant between-group mood difference limit clinical interpretation. Larger studies are needed to test whether these findings are reproducible and linked to meaningful symptom changes.