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Eating a dark chocolate bar may improve visual and cognitive functions – at least temporarily. Visual sensitivity – the ability to see in difficult conditions – was enhanced up to two hours later in people who ate the chocolate as part of a study. The results highlight the potential health benefits derived from dark chocolate and suggest new avenues of research.

What did they do?

Researchers from the University of Reading examined the visual and cognitive effects of cocoa flavanols. In the study, 30 18- to 25-year-olds ate a dark chocolate bar (CHOXI+) containing 773 milligrams cocoa flavanols during one test session and a white chocolate bar containing none at a second test session a week later. Two hours after eating the bar at each session, they were tested on visual, memory and reaction time tasks.

One visual task assessed the ability to read as light conditions change – called contrast sensitivity. After participants correctly read a set of numbers on a screen the light contrast was lowered to make the numbers more difficult to read. The contrast was again lowered after each correct response until neither of the digits was read correctly.

Other sets of visual tests used moving dots. Participants identified their direction and their pattern – either horizontal or random.

Cognitive skills were assessed through memory and reaction time tests. For memory, the participants were asked to identify which objects had changed locations from one screen to another. The reaction time task required participants to quickly press one of three keys associated with a number or two letters that flashed on the computer screen.