Okinawa, part of the Ryukyu archipelago of 161 islands that stretch between Japan and Taiwan, has long been rumoured to be home to the longest-living people in the world. Now, after a 25-year scientific study, the rumour has been proved to be fact. Its population of 1.3 million includes more than 400 centenarians - nearly four times the rate in Western countries, and more per head of population than anywhere in the world. The average age of death is 81.2 years - around five years older than that of Westerners.

But what, perhaps, is more striking is the extraordinary rude health that the elderly...