Those who consumed 500ml daily for eight weeks noticed an eight per cent improvement in the ability to process thoughts, retrieve memories and learn new information.

Orange contains flavonoids, which seem to activate important pathways in the hippocampus area of the brain, the study found.

Over a lifetime the benefits could be substantial and experts hope they have found a cheap way to keep people mentally alert for longer.

But they do not recommend continually drinking such a large amount of juice because of its high sugar content.

Dr Daniel Lamport, of the University of Reading’s School of Psychology and Clinical Language Sciences, said: “More research on the positive effects of flavonoids on cognition is needed. However, this is an important discovery.”

Flavonoids are found in green tea, apples, red wine, strawberries, blueberries and cocoa. The university’s study was published in the American Journal of Clinical Nutrition.