She emphasizes that no one has convincingly shown that young blood lengthens lives, and there is no promise that it will. Still, she says that young blood, or factors from it, may hold promise for helping elderly people to heal after surgery, or treating diseases of ageing.

“It’s very provocative,” says Mark Mattson, chief of the Laboratory of Neurosciences at the US National Institute on Aging in Bethesda, Maryland, who has not been involved in the parabiosis work. “It makes you think. Maybe I should bank some blood of my daughter’s son, so if I start to have any cognitive problems, I’ll have some help,” he says, only half-joking.