The government has confirmed that Japanese women remained the world's longest-living last year, although their average life expectancy edged down slightly to 86.39 years.
The fall of 0.05 years was the first decline in five years, falling from a record 86.44 registered in 2009, the Ministry of Health, Labour and Welfare said.
"Last year's heat wave probably led to an increase in deaths resulting from heat stroke and heart trouble," a ministry official said.
Deaths from heat stroke reached a record high of 1,718, with 80 percent of those people aged 65 and older, he said.
Among countries and areas across the world, Japan ranked first for women's longevity, followed by Hong Kong at 85.9 years and France at 84.8 years, the ministry said.
The average life expectancy of Japanese men hit a new high for the fifth straight year in 2010, rising 0.05 to 79.64 years, the ministry said.
Japan ranked fourth in men's longevity below Hong Kong at 80.0 years, Switzerland at 79.8 years and Israel at 79.7 years.