Blackberries are thought to be the best source of flavenols, which scientists believe could be key to boosting memory and sleep. Andrea Warnecke/dpa

Found in berries and teas, flavonols could be key to boosting memory and sleep - if only there was a way to get the body to absorb more of them.

A team of scientists at the Shibaura Institute of Technology in Tokyo has found that a single dose “stimulated brain regions involved in memory and sleep-wake regulation, and increased sympathetic nervous activity, a stress response.”

But although flavenols are found in a range of foods, including coffee, wine and many vegetables, they have “poor bioavailability,” according to the researchers.

This means that only “a fraction” of what gets ingested makes it as far as the bloodstream, limiting their potential impact.

The “astringent” tastes that many flavenol-rich food items and drinks come with could be key, however, as it appears this is what stimulates the brain - at least in tests on mice, which “exhibited greater motor activity, exploratory behaviour, and improved learning and memory” when given flavenols.

Flavenol intake appeared to prompt a dopamine rush, referring to the brain chemical and so-called “feel-good” hormone that plays a role in memory, stress and mood.

“Moderate intake of flavanols, despite their poor bioavailability, can improve the health and quality of life,” said Shibaura researcher Yasuyuki Fujii.

Blackberries are thought to be the best source of flavenols, with blueberries and raspberries next. Previous studies have pointed to a link between consistent intake of flavenol-rich food and reduced risk of developing breast, colon and prostate cancer.