Japan fears for its centenarian citizens - all 20,000 of them

The number of Japanese centenarians has risen to more than 20,000, setting another record in the world's longest-living country.

The figure of 20,561 is an increase of more than one hundred fold since records began in 1963, and is a jump of 2,627 in the past year.

Women account for 84 per cent of the total, including the world's oldest living person, Kamato Hongo, from the southern island of Kyushu. She will turn 116 next Tuesday. The same island is also the home of Yukichi Chuganji, who at 114 is the oldest living man.

Scientists have long speculated on the secret of Japan's centenarians, with explanations ranging from strict exercise regimes to the traditional Japanese diet, which is low in fatty foods.

The Okinawa chain of islands boasts the most centenarians per head of population, with 34.67 per 100,000, a fact sometimes attributed to a combination of its subtropical climate and the people's traditional diet - local specialities include vegetables, fruit and bean curd.

Mr Chuganji seems to be a living rejection of the dietary theories - he hates eating vegetables and lists meat as one of his passions.

Other senior citizens each had their own explanation. Miyuki Lida, 100, credited fresh-squeezed lemon juice. Ms Hongo's 79-year-old daughter was quoted as saying the world's oldest woman "grew up in a warm household surrounded by her parents and siblings".

Japan has the world's highest life expectancy, at 78 years for men and 85 for women and the growing number of people who have lived for more than a century is a source of national pride.

But a falling birth rate has raised concerns over Japan's ability to support its ageing population. This rapid ageing of Japanese society and the tumbling birthrate - last year it was recorded at a record low of only 1.35 births per woman - have raised concerns that pension obligations may become unmanageable.

Almost a fifth of the Japanese population (23.63 million) is over 65, with some estimates speculating that the figure will rise to roughly one person over 65 for every two of working age by 2025 - a higher dependency ratio than any other big industrialised nation.

The speed of ageing of Japan's population is much greater than that of Western countries. According to the Statistical Handbook of Japan 2003 the population of the elderly in Japan jumped by 7 per cent in 24 years - a similar increase took 85 years in Sweden and more than 100 years in France.