In what could be a fresh chapter in the never-ending story of the search for eternal youth, scientists are to tinker with people’s blood in the hope of slowing down the ageing process and preventing age-related diseases.

Researchers in California plan to launch a clinical trial of the radical – and highly experimental – approach in the next six months, after a small study in mice found the treatment had promise.

People who take part in the trial will have their blood passed through a machine that resets abnormal levels of proteins seen in older blood. The scientists believe these high levels of certain proteins can hamper the growth and maintenance of healthy body tissues, and so contribute to their deterioration in old age.

Plans for the trial emerged as scientists announced the results of the animal study, which was part-funded by Calico, Google’s life extension company. The study showed that infusions of old blood reduced the growth of fresh liver and brain cells in young mice and impaired their performance in a strength test.

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