Blackcurrant juice increases blood flow in the brain’s prefrontal cortex

A new study published in Nutritional Neuroscience provides evidence that drinking blackcurrant juice may increase blood flow in the brain’s frontal regions during both rest and mental effort. The study, conducted in healthy young adults, found that those who drank a polyphenol-rich blackcurrant juice showed significant changes in blood oxygen levels in the prefrontal cortex, a brain area involved in decision-making and attention. However, these changes did not translate into improved performance on mental tasks.

Blackcurrants are rich in compounds called polyphenols, especially anthocyanins. These natural plant chemicals have been linked to improved heart and blood vessel health in past studies. There is also growing interest in whether polyphenols can influence brain function, particularly by improving blood flow to key areas involved in thinking and memory.

“This project is part of a larger body of work that I’ve been undertaking for the past 10 years investigating potential effects of blackcurrants on brain health,” said study author Anthony Watson, the principal investigator of the Human Nutrition and Exercise Research Centre at Newcastle University.

Earlier research by the same team found that blackcurrants might impact neurotransmitters like dopamine and serotonin by blocking the enzyme monoamine oxidase. This enzyme is known to break down these brain chemicals, and blocking it may help maintain their levels. The researchers had also shown that blackcurrants can influence brain wave activity, particularly in the frontal cortex. Based on these earlier findings, they hypothesized that blackcurrant juice might improve blood flow in the same part of the brain, possibly supporting mental performance.

To test their theory, researchers used a controlled experiment involving 20 healthy adults aged 18 to 35. Each participant visited the lab on two different days. On one day, they drank a special blackcurrant juice made from a variety known as “Blackadder,” which had been processed to contain 500 milligrams of polyphenols. On the other day, they consumed a placebo drink that looked and tasted the same but did not contain polyphenols. The study followed a crossover design, meaning all participants tried both drinks in a random order.

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After consuming the drink, participants rested for one hour to allow the polyphenols to enter the bloodstream. During this rest period and afterward, their brain blood flow was measured using a non-invasive technique called near-infrared spectroscopy. This method shines light through the skull to track changes in oxygen levels in the blood, providing a picture of how much blood is flowing in the brain’s surface areas.

Following the rest period, participants completed a series of mentally demanding tasks designed to activate the prefrontal cortex. These included two types of arithmetic problems and a task that required monitoring rapidly changing numbers on a screen. Participants also rated their feelings of mental fatigue.

The most striking result was that drinking the blackcurrant juice led to a measurable change in blood flow in the brain. Specifically, oxygenated hemoglobin—an indicator of blood carrying fresh oxygen—increased in the left side of the prefrontal cortex during mental tasks. At the same time, levels of deoxygenated hemoglobin dropped, suggesting more efficient oxygen delivery and use. These patterns began to appear around 35 minutes after drinking the juice and continued through the end of the session.

Interestingly, this change was not seen on the right side of the brain, indicating a possible lateralized effect. This aligns with earlier imaging studies suggesting that the left prefrontal cortex is more active during tasks involving working memory.

The researchers also observed that total hemoglobin, which reflects overall blood volume in the area, increased slightly in the left hemisphere following juice consumption. These findings are consistent with increased blood flow to that region, possibly due to a response known as neurovascular coupling. This process involves blood vessels expanding in response to increased brain activity, ensuring the area gets enough oxygen and nutrients.

Despite these physiological changes, participants did not perform any better on the mental tasks after drinking the blackcurrant juice. Their speed, accuracy, and self-reported fatigue were similar whether they consumed the juice or the placebo.

The lack of improvement in task performance suggests that simply increasing blood flow may not be enough to boost cognition in healthy young adults who already have optimal brain function. It is possible that these individuals were already performing near their best, leaving little room for improvement. Another possibility is that the mental tasks used, while demanding, were not sensitive enough to detect small differences in cognitive performance.

The left-sided increase in blood flow raises questions about how blackcurrant polyphenols affect the brain. One idea is that the anthocyanins or other compounds in the juice may promote the release of nitric oxide, a molecule that helps widen blood vessels. Another possible explanation is that the juice’s effect on neurotransmitters like dopamine or serotonin may play a role. Dopamine, in particular, has been linked to blood flow regulation in animal studies and may help explain the observed changes.

This study was small, with only 20 participants, and focused on a very specific age group—young adults in good health. The researchers acknowledge that this group may not benefit as much from blood flow changes as older adults or individuals with impaired circulation. Larger studies involving different age groups or people with reduced cognitive function could help determine whether blackcurrant juice offers more obvious mental benefits in those populations.

Another limitation is that only the prefrontal cortex was examined. While this region is important for attention and decision-making, it is just one part of a much larger brain network involved in cognition. It’s not clear whether blackcurrant juice would have similar effects elsewhere in the brain.

The researchers also did not measure levels of vitamins or minerals in the juice, which could have contributed to the observed effects. Blackcurrants are naturally high in vitamin C and other nutrients, which may also influence blood flow. Future studies might aim to control for these factors more precisely.

Finally, the researchers note that participants’ diets were not closely monitored. Regular intake of polyphenols may influence how the body responds to a single dose, so future work may need to consider habitual dietary patterns.

“The current paper is another small piece of a jigsaw of evidence which demonstrates the influence blackcurrant consumption can have on the brain,” Watson said. “Our work continues and, if funding applications are successful, the next project will use MRI to understand the effects blackcurrant have on the brain.”

The study, “Effects of blackcurrant juice on pre-frontal cortical haemodynamics and cognition in healthy young adults,” was authored by Anthony W. Watson, Arjan Scheepens, David O. Kennedy, and Crystal F. Haskell-Ramsay.