One cup a day of wild blueberries can speed up reaction times, strengthen short term memory and improve executive function, as well as provide a brain boost, lower blood pressure, and contribute to better cardiovascular health, a study from King’s College London Faculty of Life Sciences and Medicine has found.
The randomised, double-blind, placebo-controlled trial involved participants consuming a daily drink of 26 grams of freeze-dried wild blueberry powder for 12 weeks: they showed a 3.59mm of mercury (mmHG) reduction in systolic blood pressure, and improved blood vessel function compared with individuals consuming a placebo powder.
Those who drank blueberries were better at immediately recalling word lists, and exhibited improved switching accuracy. The researchers observed no improvement in delayed recall, however.
The study, which was published in the American Journal of Clinical Nutrition, involved 61 healthy male and female participants from London, aged between 65 and 80. Over 12 weeks, half of them drank a daily beverage containing 26g of freeze-dried wild blueberry powder, while the other half consumed a taste-, appearance-, macro-nutrient-, fibre-, and vitamin C-matched placebo.
The 26g of blueberry powder participants consumed daily was the equivalent of 178g of whole blueberries – somewhere between 75–80 blueberries, since they vary in size.
Senior investigator Dr Ana Rodriguez-Mateos told Medical News Today that the blueberries need not be wild, since “there have been other studies conducted with other types of blueberries showing benefits in cognitive and vascular health”.
Anthocyanins: healthy natural pigments
The researchers believe the blueberries’ beneficial effects are due to their blue pigments called anthocyanins. Each daily dose of wild blueberry powder in the study contained 302mg of anthocyanins. The placebo beverage contained none.
Anthocyanins are a class of polyphenols, and Michelle Routhenstein, a heart health dietitian not involved in this study, said there were about 8 000 different types of these that provide health benefits. “Some other foods that have beneficial polyphenols include green tea, broccoli, pears, and spices like turmeric and cinnamon.”
Anthocyanins are also present in strawberries, raspberries, red grapes and purple vegetables.
How the study came to be
Rodriguez-Mateos and co-author Dr Claire Williams had been separately investigating the cognitive and cardiovascular benefits of blueberries, and seeing similar results.
They decided to investigate the effects on vascular and cognitive function simultaneously in one clinical study. They set out to measure cerebral blood flow, as other research has suggested it may be a mechanism behind polyphenols’ beneficial effects, along with increased vascular blood flow.
In addition, recent insights into the gut microbiota and gut-brain axis prompted them to explore this relationship as well.
What polyphenols may be doing
The mechanism behind the beneficial effects of polyphenols is not yet fully understood.
“One theory is that polyphenol metabolites may act as signalling molecules, acting through several cell-signalling pathways, modulating nitric oxide bioavailability and different enzymes,” said Rodriguez-Mateos.
The researchers found increases in anthocyanin metabolites in participants’ urine after the 12-week study period.
They are certain that the mechanism of action in the blood vessels is endothelium-dependent and therefore mediated through the nitric oxide pathway.
While the study found evidence that blueberries improved cerebral and vascular blood flow, they saw no difference in arterial stiffness and blood lipids between people consuming the fruit and the placebo group.
Still, “when blood flow is improved, both heart and brain health benefit”, said Routhenstein.
As far as the role of gut microbiota goes, Rodriguez-Mateos said: “A hypothesis we proposed in our study is that polyphenols may act via enhancing the abundance of butyrate-producing beneficial bacteria, and therefore, the production of butyrate.”
She added this needs to be confirmed in further studies.
Study details
Wild Blueberry (Poly)phenols can Improve Vascular Function And Cognitive Performance In Healthy Older Males And Females: A Double-Blind Randomised Controlled Trial
Eleanor Wood, Sabine Hein, Robin Mesnage, Lynne Bell, Claire Williams, Ana Rodriguez-Mateos.
Published in The American Journal of Clinical Nutrition on 25 March 2023
Abstract
Background
Evidence suggests that intake of blueberry (poly)phenols is associated with improvements in vascular function and cognitive performance. Whether these cognitive effects are linked to increases in cerebral and vascular blood flow or changes in the gut microbiota is currently unknown.
Methods
A double-blind, parallel randomised controlled trial was conducted in 61 healthy older individuals aged 65-80 y. Participants received either 26g of freeze-dried wild blueberry (WBB) powder (302 mg anthocyanins) or a matched placebo (0 mg anthocyanins). Endothelial function measured by flow-mediated dilation (FMD), cognitive function, arterial stiffness, blood pressure (BP), cerebral blood flow (CBF), gut microbiome and blood parameters were measured at baseline and 12 weeks following daily consumption. Plasma and urinary (poly)phenol metabolites were analysed using micro-elution solid phase-extraction coupled with LC-MS.
Results
A significant increase in FMD and reduction in 24 h ambulatory systolic BP were found in the WBB group compared to placebo (0.86%; 95% CI 0.56, 1.17, p<0.001; -3.59 mmHg; 95% CI -6.95, -0.23, p=0.037; respectively). Enhanced immediate recall on the auditory verbal learning task, alongside better accuracy on a task-switch task were also found following WBB treatment compared to placebo (p<0.05). Total 24 h urinary (poly)phenol excretion increased significantly in the WBB group compared to placebo. No changes in CBF or gut microbiota composition were found.
Conclusions
Daily intake of WBB powder, equivalent to 178 g fresh weight, improves vascular and cognitive function, and decreases 24h ambulatory systolic BP in healthy older individuals. This suggests that WBB (poly)phenols may reduce future cardiovascular disease (CVD) disease risk in an older population, and may improve episodic memory processes and executive functioning in older adults at risk of cognitive decline.
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Plant-based diet lessens risk of cognitive impairment — 12-year European study
Flavonoids may have protective benefits against Alzheimer’s and related dementias
Cranberries could improve memory, fight dementia – British collaborative study