It is supposed to be the perfect bedtime drink to send you off to sleep. But in fact, a cup of hot chocolate could be just the thing to peep you up, scientists say.
Research shows that flavanols - plant chemicals abundant in dark chocolate - stave off fatigue and boost mental sharpness. It is thought that they widen blood vessels, boosting blood flow to the brain.
Psychologists asked 30 people to carry out a battery of mental arithmetic tests before and after having a flavanol-rich chocolate drink or a dummy beverage. They found the sweet drink boosted performance on one of the tests, which involved repeatedly subtracting the number three from a start point of between 800 and 999.
The flavanols also appeared to counteract the tiredness brought on by doing the intensive arithmetic, the British Psychological Society's annual conference heard.
Researcher Crystal Haskell (CORR) said: 'We asked them about their mental fatigue and that increased but the cocoa offset that increase.'
The study, carried out at the Brain, Performance and Nutrition Centre at Northumbria University, also found that a 500mg dose of flavanols was more effective than a higher one.