A pilot study of daily blueberry intake modulates the gut microbiota enzyme commissions in older, sedentary adults with mild depressive symptoms

BACKGROUND: Fiber and anthocyanins in blueberries have potential to modify the gut microbiome and metabolites that are relevant to depression in older adults. OBJECTIVE: Our objective was to preliminarily determine the effect of blueberry consumption on the gut microbiome, metabolites, and depressive symptoms. DESIGN: Sedentary, older adults (≥65y) with mild depressive symptoms were enrolled in a randomized, double-blind, parallel-arm, placebo-controlled pilot study. Participants consumed 48 g/day of blueberry powder (∼2 cups of fresh berries) or placebo for 3 months. Metagenomic sequencing measured the abundance of fecal bacterial species and genes, liquid chromatography/mass spectrometry evaluated gut-derived fecal short chain fatty acids (SCFA), and validated questionnaires evaluated depressive symptoms before and after the intervention. PARTICIPANTS: Eighteen participants who were predominantly female and white completed the intervention (Placebo Group, n = 8, mean age: 75 ± 6; Blueberry Group, n = 10, mean age: 71 ± 4). RESULTS: Measures of species abundance, MetaCyc pathways, and metabolites did not change. There were statistically significant in the gene abundance of several Enzyme Commissions (EC) of the gut microbiome within the Blueberry Group-including EC 3.6.3.31 Polyamine Transporting ATPase, which is involved in the production of the neurotransmitter, gamma-aminobutyric acid (GABA). CONCLUSION: While there were no statistically significant differences in changes in depressive symptoms between groups, the magnitude of reduction in depressive symptom severity appeared greater, with smaller variability in the Blueberry Group, which was paired with minor changes in the gut microbial ECs. Our data are preliminary and warrant additional studies to investigate the link between blueberries, the gut-microbiome, and mood in older adults.