OKINAWA IS famed for the longevity of its residents. The small Japanese island, far south-west of the mainland, boasts a life expectancy for 65-year-old women that is almost a year higher than the country-wide average, and around four years more than that of Britain or America.
As a result, researchers seeking a life-extending elixir (see Technology Quarterly) have long looked to Okinawans for their secret. Eating a vegetable-rich diet, staying active and having a sense of purpose have all been suggested as candidates. But one pre-print study provides a more prosaic explanation for remarkable reported longevity in certain parts of the world: data errors.
Estimates of the ages of the exceptionally elderly are often inaccurate. Few very old people have birth certificates. Some do not know their true age. And public records can be woefully unreliable. A government audit in 2010 uncovered 230,000 supposedly living Japanese centenarians who were dead or missing. Some errors are genuine mistakes, but others may be the result of deliberate efforts by individuals or family members to commit pension fraud.
Saul Newman of Oxford University set out to test whether such errors could explain why some places appear to be longevity hotspots. He gathered numbers of centenarians, semi-supercentenarians (those over 105 years old) and supercentenarians (those over 110) ostensibly living in areas of America, Britain, Italy, France and Japan using a patchwork of death records, censuses and databases logging old people.
Dr Newman found that clusters of high reported longevity tended to occur in areas where record-keeping might conceivably be more lax, or where residents might have more incentive to claim pensions fraudulently. In Britain, Italy, France and Japan records showed old people living in poorer, crime-ridden areas as more likely to reach extraordinary ages. Okinawa, for example, has a poverty rate nearly twice the Japanese average and 1.6 times as many listed centenarians for each reported nonagenarian.
There were also curious paradoxes in the distribution of centenarians that could be easily explained by reporting errors. In Italy provinces where more people reach the age of 105 tend to have more people die before 55. On the island of Sardinia, renowned for its abundance of very old people, residents have among the lowest chances of reaching midlife of any Italians.
The most concrete evidence that mistakes could be causing variations in the numbers of very old people came from America. Between 1841 and 1919, states introduced birth certificates, making age estimates more accurate and fraud more difficult. By aligning data on the numbers of old people in each state with the date that birth registration was introduced, Dr Newman found that it resulted in a 69% drop in the prevalence of supercentenarians.
Differences in lifestyle and health care probably cause variability in life expectancy across countries, but they cannot fully explain why some places appear to have so many centenarians. One secret to a longer life? Throw away your birth certificate. ■
