As we heard in a government white paper on the elderly last week, the number of people aged 90 or over topped 1 million in Japan for the first time in 2004. Japan has long held the record for its citizens having the longest life expectancy in the world. And the government is only too aware of the graying population, which combined with a record low birth rate -- an average of only 1.29 children per woman -- is certain to cause economic problems in the near future.

At the current rate, there will be only 64 million people in the country by the end of the century, and many of those will be elderly. But why do people live so long in Japan?

The standard answers point to a good diet, good health care and good support for the elderly -- all of which certainly play an important part in keeping Japan at the top of the world's longevity league. But I like to think (without any really solid evidence, it has to be said) that there is something else going on too.