Americans, on average, can expect to live to about age 76, according to the US government. UN data is a bit more optimistic, putting the American life expectancy at 79.9, (compared with 83 in Australia). But health starts to decline earlier – at 64 for Americans.

Some longevity influencers have gained notoriety by focusing on that first number, claiming they can radically extend human life with experimental drugs or laborious diet, exercise and supplement protocols. But most experts who study ageing are trying to target the second element: not our lifespans, but our “health spans” – the number of years a person lives without serious disease, particularly those related to ageing.