Depressive symptoms fell more consistently, not significantly, with eating blueberries every day—a surprising effect on mood

Testing blueberries and mood

Researchers recruited physically inactive adults aged 65 and older who had mild depressive symptoms. The randomized, double-blind pilot study compared daily blueberry powder with a matching placebo over three months.

Participants received either 48 grams of blueberry powder a day, roughly equivalent to two cups of fresh berries, or placebo powder. Eighteen people completed the study: 10 in the blueberry group and eight in the placebo group. Most participants were women, and the group was predominantly white.

Mood results remain uncertain

Participants taking blueberry powder showed a greater and more consistent decline in depressive symptoms. However, the difference in mood improvement between the blueberry and placebo groups was not statistically significant.

The results therefore do not establish that eating blueberries can relieve depression. The researchers described the findings as preliminary evidence for a possible link among blueberry consumption, gut microbes and mental health.

Changes in microbial genes

Researchers analyzed gut microbes through metagenomic sequencing and measured fecal short-chain fatty acids. They found no overall changes in microbial species, MetaCyc metabolic pathways or these metabolites. Within the blueberry group, however, genes associated with several gut microbial enzymes changed significantly. One was EC 3.6.3.31 Polyamine Transporting ATPase, an enzyme involved in producing GABA, a neurotransmitter that has a role in brain signaling.

Further research needed

Lead author Courtney L. Millar said blueberry fiber and anthocyanins could affect gut microbes and metabolites relevant to depression in older adults. The study set out to examine those measures alongside depressive symptoms.