As we age, our metabolism slows and our immune system runs out of steam. Older people are more likely to have severe cold and flu symptoms, probably because they have fewer fresh immune cells left. And a slower metabolism means that glucose stays in the blood stream for longer after eating a meal. Over time, high blood sugar levels can damage organs.

But experiments in mice suggest that transplanting organs from a younger individual could reverse these changes. Jeffrey Mason at Utah State University in Logan removed the ovaries of 10 mice that were 12 months old and had gone through oestropause, a transition similar to the human menopause. He replaced these with ovaries taken from 60-day old mice – roughly equivalent to people in their early 20s in terms of ageing.