Chocolate, tea, grapes and blueberries seem to have nothing in common except the fact they share a molecule found to improve memory abilities in mice.

Further trials at the Salk Institute assessed if epicatechin has the same effects on humans.

Previous researches showed that epicatechin improves the brain blood flow, especially when combined with extra exercise. Still, nutritionists do not see chocolate as a solution for improving memory, due to its high levels of fat and sugar, which counterbalance potential benefits. Other researches too connected "flavanol" molecules encountered in certain foods and health benefits, like better cardiovascular health function.

The research team led by Dr Henriette van Praag collaborated with chocolate firm Mars. They made a comparison between mice fed on a typical diet with those fed on a diet containing additional epicatechin. 50 % of the mice in each group could run on a wheel for two hours daily and then, a month later, were trained to track down a platform hidden in a pool of water.

The individuals that both exercised and were fed on the epicatechin diet performed the best on the platform location exercise.

Mice fed on epicatechin but without exercising displayed boosted memory, but to a lesser level.

The mice on the epicatechin diet seemed to display greater blood vessel growth in certain brain areas, alongside more mature brain neurons. "A logical next step will be to study the effects of epicatechin on memory and brain blood flow in aged animals - and then humans, combined with mild exercise." said van Praag.

"This is an important advance because it identifies a single natural chemical with memory-enhancing effects, suggesting it may be possible to optimise brain function by combining exercise and dietary supplementation." said Dr Mark Mattson, from the US National Institute on Aging.

"While there was some evidence that diets rich in flavanols could be beneficial in humans, often when flavanols such as epicatechin were given on their own, no benefits could be spotted. We'd obviously recommend a diet rich in fruit and vegetables, with perhaps a small amount of chocolate - but eating five bars a day is likely to just make you fatter, without any noticeable improvement in memory", said a spokesman for the British Nutrition Foundation.