Their longevity increased by 160 days from 2005 "as there was an improvement in what are considered the three major causes of deaths among the Japanese -- cancer, heart disease and strokes," a health ministry official said.
"There also were fewer deaths from influenza among the elderly in 2006 compared with the previous year," he said.
Japanese women are believed to be longest-living people in the world, according to data divided by gender. Hong Kong women came second at 84.6 years, according to figures by individual governments and the United Nations.
Swiss and Spanish women were tied for third at 83.9 years.
Japanese men are also living longer, with average lifespans up 106 days to 79.00 years, the health ministry said.
But Icelandic men, who live an average of 79.4 years, pushed Japanese men into second place. Hong Kong men were third, living 78.8 years on average.
Japan, with its traditional healthy diet and high standard of medical care, has one of the oldest populations.
But the longevity is also causing headaches for policymakers, who fear a future demographic crisis with a smaller pool of young people supporting a mass of elderly.
Last month the government forecast that two in every five Japanese people will be 65 or older by 2055 if the trends of a low birthrate and high life-expectancy continue.