A randomized, double-blind pilot study from Hebrew SeniorLife's Marcus Institute tested whether daily blueberries affect mood and gut microbes in older adults. Participants aged 65 and older with mild depressive symptoms consumed either 48 grams of blueberry powder (roughly two cups of fresh berries) or a matching placebo powder every day for three months.
The 18 completers showed no statistically significant difference in mood improvement between groups, though the blueberry group had a greater and more consistent reduction in depressive symptoms. Metagenomic sequencing and fecal metabolite analysis found no overall changes in microbial species, metabolic pathways, or short-chain fatty acids. However, researchers detected significant shifts in genes for several gut microbial enzymes, including polyamine transporting ATPase, which is involved in the production of the neurotransmitter GABA.
The authors suggest that fiber and anthocyanins in blueberries may modify the gut microbiome and metabolites relevant to depression in older adults, but they caution that larger studies are needed to confirm any connection. The study was published in the Journal of Nutrition, Health and Aging.