Daily Blueberries May Help Ease Depression Symptoms in Older Adults

Fruit contains a wide range of beneficial compounds, and researchers continue to examine how those nutrients may support mental health as well as physical health.

A small pilot study led by Harvard Medical School researchers in the United States suggests that eating blueberries every day may help reduce symptoms of depression in older adults who are mostly inactive.

That matters because older people face a higher risk of depression, and many do not have easy access to some of the usual ways to help manage it, such as regular exercise and time outdoors.

Blueberries could therefore offer a simple, nutritious way to help support mood.

The findings were published in the Journal of Nutrition, Health and Aging, and the study also pointed to changes in gut bacteria after blueberry intake.

“Our objective was to preliminarily determine the effect of blueberry consumption on the gut microbiome, metabolites, and depressive symptoms,” said molecular nutritionist Courtney Millar of Harvard Medical School.

The trial included 18 participants aged 65 and older, who received either 48 grams of freeze-dried blueberry powder each day, roughly equivalent to about two cups of berries, or the same amount of placebo powder.

After three months, depressive symptoms improved in both groups. The blueberry group showed larger and more consistent gains, although the difference was not statistically significant.

“While changes in mental well-being outcomes are not different between groups, they appear to be ‘improvements’ of stronger magnitude in the blueberry group, with less variability compared to the placebo group,” the researchers wrote in their paper.

“This pilot study was designed to test intervention feasibility and gather the preliminary data on outcomes that are needed to estimate power of a larger trial.”

There were also modest changes in gut microbes among the blueberry participants, including shifts in enzyme genes related to chemical activity.

Six bacterial enzyme genes changed in abundance, five of them increasing. One of the genes was linked to the production of gamma-aminobutyric acid, or GABA, a neurotransmitter previously associated with depression.

Because blueberries already are known to influence the gut microbiome through fiber and anthocyanins, some changes were expected. Still, more detailed research is needed to understand exactly what is happening.

The researchers also noted the study’s limitations, including its small sample size and the fact that most participants were female and white, and had mild depressive symptoms rather than a formal diagnosis of depression.

Although the results do not support broad conclusions, they provide a foundation for larger studies.

The team said future research should include more diverse participants and “recruit a larger sample size to account for the effect of potential confounders and baseline differences.”

The lack of a statistically significant difference between the blueberry and placebo groups may seem discouraging, but the more consistent symptom improvements and the microbiome changes suggest follow-up work is worthwhile.

The placebo effect may also have played a role, since people in the placebo group could have felt better simply because they believed they were taking something beneficial.

The connection between the brain and the gut is complex and bidirectional, and scientists are still working to understand it. Evidence is growing that diet can influence mental health, and this study adds to that body of research.

“Our data are preliminary and warrant additional studies to investigate the link between blueberries, the gut microbiome, and mood in older adults,” the researchers wrote.

The research appeared in The Journal of Nutrition, Health and Aging.