Cocoa can help to slow and even reverse age-related memory loss, according to a study pointing to the previously unknown mental benefits of the chocolate ingredient.
Scientists believe that flavanols, the antioxidants inside cocoa beans, can give people in their sixties the memory of a "typical 30- or 40-year-old".
The study, by the Columbia University Medical Centre in New York, is thought to be the first evidence that age-related memory decline - a common problem that can cause older people to forget small things like the names of acquaintances or where they have placed their keys - can be countered through dietary changes.
The trials involved 37 volunteers, aged between 50 and 69, divided into two groups. One group was administered daily drinks with a high (900mg) dosage of flavanols, while the other was offered just 10mg a day. After three months, the group that drank the high intake showed signs of faster and clearer recognition of visual patterns. Brain scans before and after the trial showed more blood within the dentate gyrus part of the hippocampus, one of the few regions known to generate fresh brain cells.
"If a participant had the memory of a typical 60-year-old at the beginning of the study, after three months that person on average had the memory of a typical 30- or 40-year-old," said the senior author, Dr Scott A Small.
Dr Ashok Jansari, cognitive neuropsychologist at Goldsmiths College, said: "Given a globally ageing population, by isolating a particular area of the brain that is weakening in functioning as we grow older, and demonstrating that a non-pharmacological intervention can improve learning of new information, the authors have made a significant contribution to helping us improve our cognitive health."
The study, published in the online periodical Nature Neuroscience, follows research indicating cardiovascular benefits from cocoa. However, experts said the study did not mean people should eat more chocolate, as the product used in the experiment was a specially made drink formulated from cocoa beans.
The research did not look at the impact of cocoa on dementia, which is different to age-related memory decline.
Dr Simon Ridley, of Alzheimer's Research UK, said: "This very small trial highlights some possible effects of flavanols found in cocoa beans over a short time period, but we'd need to see much longer, large-scale studies to fully understand whether a diet high in these flavanols could boost cognition in old age."
Dr Liz Coulthard, a senior lecturer in dementia neurology at the University of Bristol, said: "Only reaction times, and not accuracy of performance, were actually improved and being faster without being more accurate is not always an advantage."