Blueberries are often praised for their nutritional value, but could they also have a role in supporting emotional wellbeing as people age? A small pilot study has explored this possibility, examining whether daily blueberry consumption might influence depressive symptoms alongside changes in the gut microbiome. The findings offer an intriguing lead, rather than a definitive answer. Older adults who consumed blueberry powder for three months showed a reduction in depressive symptoms over time. However, the researchers did not find a statistically significant difference in symptom changes between those who received blueberries and those given a placebo. The results need to be interpreted cautiously, especially because only 18 participants completed the study.Published in ‘The Journal of Nutrition, Health & Aging‘, the research examined a possible relationship between blueberries, gut microbial activity and mood in older adults who were physically inactive and experiencing mild depressive symptoms.
What did the researchers investigate?
The study focused on adults aged 65 and above who led sedentary lifestyles and reported mild depressive symptoms. Researchers were interested in two components found in blueberries: dietary fibre and anthocyanins, the natural pigments responsible for the berries’ blue-purple colour.Both have attracted scientific interest for their potential effects on gut health. Fibre can be used by gut microbes, while anthocyanins are plant compounds that may influence biological processes associated with health. The researchers wanted to investigate whether consuming blueberries could alter gut microbial activity and related metabolites in ways that might be relevant to mood. As lead author Courtney L. Millar explained, the objective was to make a preliminary assessment of the effects of blueberry consumption on the gut microbiome, metabolites and depressive symptoms. The study was published under the title “A pilot study of daily blueberry intake modulates the gut microbiota enzyme commissions in older, sedentary adults with mild depressive symptoms.”
How the three-month experiment worked?
The researchers used a randomised, double-blind, placebo-controlled design. Participants were assigned to receive either 48 grams of blueberry powder daily or a similar-looking and tasting placebo powder for three months. The blueberry dose was described as equivalent to approximately two cups of fresh blueberries. Of the 18 participants who completed the intervention, 10 were in the blueberry group and eight were in the placebo group. Most participants were women and white, which is an important limitation when considering whether the findings apply to a wider population.Researchers assessed depressive symptoms using validated questionnaires before and after the intervention. They also analysed stool samples to examine gut microbial species, microbial genes and short-chain fatty acids, which are compounds produced when gut microbes process certain nutrients. The small sample size means the results should be treated as preliminary. Larger studies involving more diverse groups of participants will be needed to establish whether the observed patterns can be reproduced.
What changed in the gut microbiome?
The researchers did not observe changes in the measured abundance of gut microbial species, metabolic pathways or short-chain fatty acid metabolites. However, they identified statistically significant changes in the abundance of genes associated with several gut microbial enzyme functions within the blueberry group. One finding involved a polyamine-transporting ATPase enzyme classification. The researchers noted its relevance to biological processes associated with gamma-aminobutyric acid, or GABA, a neurotransmitter involved in nervous system signalling.This does not establish that eating blueberries increased GABA levels in the brain or directly changed mood through that pathway. The findings concerned markers of microbial enzyme-related activity, and further research is required to understand their significance.
Can blueberries be considered a mood booster?
The study offers a reason to investigate the gut-brain connection further, but it does not show that eating blueberries every day prevents or treats depression. Although depressive symptoms declined in the blueberry group, the change was not significantly different from that in the placebo group. Blueberries can still form part of a balanced diet, providing fibre and other beneficial plant compounds. But this study does not establish a specific daily quantity that improves mood, nor does it show that the findings apply to younger adults or people with more severe depression.Anyone experiencing persistent low mood should seek advice from a qualified healthcare professional rather than relying on a particular food as treatment. The researchers’ next step is to investigate the potential relationship between blueberry intake, gut microbial activity and emotional wellbeing in larger and more robust studies. For now, the message is one of possibility, not proof: blueberries may be worth studying as part of the broader relationship between diet, gut health and mood, but stronger evidence is needed before they can be recommended specifically for improving depressive symptoms.
