Eating Blueberries Every Day Could Reduce Depressive Symptoms in Older Adults

There's a lot of goodness packed inside the fruits we eat, and scientists continue to look at how that goodness might benefit our mental as well as our physical health.

In a small pilot study, researchers led by a team at Harvard Medical School in the US found hints that a daily dose of blueberries may help ease the symptoms of depression in older, sedentary adults.

This is a group of people who we already know are at a higher risk of depression, and who don't necessarily have easy access to some of the natural ways of tackling it – including exercising and getting outdoors.

Eating blueberries every day might be a simple, healthy way of keeping depression at bay.

The researchers have now published their work in the Journal of Nutrition, Health and Aging, and the study showed some interesting gut bacteria shifts caused by the extra blueberries too.

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

The study involved 18 participants aged 65 and older, who were either given 48 grams of freeze-dried blueberry powder every day (about two cups' worth of berries) or the same amount of placebo powder.

After three months, depressive symptoms had improved in both groups. Those in the blueberry group showed bigger and more consistent improvements, though the difference didn't reach statistical significance.

"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," write the researchers in their published 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."

In terms of gut bacteria, there were some small changes in the enzymes (proteins triggering chemical reactions) present in the blueberry participants.

Six types of bacterial enzyme genes changed in abundance, five of them rising, including one involved in making gamma-aminobutyric acid (GABA), a neurotransmitter previously linked to depression.

It's already well-established that fiber and anthocyanins (blue pigments) in blueberries can have an effect on the gut microbiome, so some shifts were expected – and a more detailed analysis will be needed to confirm exactly what's going on.

The researchers also acknowledge the relatively small sample size here, and that the participants were mostly female and white, with mild depressive symptoms rather than diagnosed depression.

While we can't make any grand conclusions from the results published here, it sets the stage for bigger studies.

The researchers say further studies should involve more diverse populations and "recruit a larger sample size to account for the effect of potential confounders and baseline differences."

That there was no statistically significant difference between the blueberry and placebo group might make you think there's nothing to see here – but the bigger, more consistent improvements in symptoms, coupled with the gut microbiome shifts, are reasons to run follow-up studies.

We also know that the placebo effect has been shown in study after study. You could argue that even the thought of a daily dose of blueberry powder was enough to lift the moods of the placebo group participants.

The brain and the gut have a complex, two-way relationship that scientists are still trying to understand. There's already some notable evidence that what we eat in our diets can have an effect on mental health, and this small study adds to it.

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

The research has been published in The Journal of Nutrition, Health and Aging.