Young blood: The plasma in young people is said to hold the key to reversing ageing in the brain

The claim, made by California-based research company Alkahest, suggests that proteins in adolescent blood can actually rebuild damaged cells and u-turn age-related deterioration.

Using donations from 18 year-olds, the researchers gave middle-aged mice two doses of human blood each week and monitored the reactions.

Prior to the treatment, the mice aged as standard – showing reduced speed and diminished memory.

But, following three weeks of the transfusions, that all changed – with the rodents developing new brain cells and exhibiting greater speed, agility and reaction times.

The study's author, Sakura Minami, said that her team had seen a "rejuvenation effect" on the mice – something which held promise for a possible human treatment, particularly for those suffering from Alzheimer's disease.