Japanese women had a life expectancy of 85.59 years in 2004, making them the world’s longest living group for the 20th consecutive year, the government said on Friday.

Japanese men trailed with a life expectancy of 78.64 years, which placed them second for longevity after Icelandic men, who live an average of 78.8 years.

The government attributes Japanese longevity to a range of factors, including a healthy diet and improving medical care, a spokeswoman for the Health Ministry said.

The Japanese diet tends to be rich in vegetables and fish products and relatively low in animal fats.

But long life expectancies combined with a tumbling birth rate may be storing up problems for Japan, where one in five of the population is over 65 and the figure is expected to jump to one in four in the next decade.

Women in Hong Kong were the second longest living group in the world, according to Japanese government figures, followed by Swiss women.