A study of how long men and women are living in 18 wealthy countries has found that life expectancy is on the rise in Australia but declining in Britain, the United States and several other nations.

Australian women had a life expectancy of 85.5 years in 2016, while for men it was 81.5 years, the study by researchers at Princeton University and the University of Southern California found.

Both Australian men and women are now living more than a year longer than they were in 2010.

By comparison, British women and men have seen their life expectancy dip to 82.7 years and 79 years respectively.

There's been a similar pattern in the US, where men now live an average of 76.4 years and women for 81.4 years.

Overall, Switzerland has the longest life expectancy for men at 81.6 years, while Japanese women live to a ripe old age of 87.2 years.

Japanese people live the longest with women having an average life span of 87.2 years and men 81 years.

The researchers said while Australia's life expectancy rates have increased uninterrupted since 2010, about 12-of-the 18 OECD countries experienced an unusual simultaneous drop in 2014-15.

While they blamed the fall largely as a result of a severe flu season, the researchers said it was the first time in decades that so many wealthy countries experienced a decline in the one year.

Most of those countries bounced back the following year, but the US and Britain did not.

The researchers suggested that the opioid epidemic gripping the US could be to blame for the decline in life expectancy there, while in the UK it could be the result of higher mortality rates among the over 65s.

The findings were published by the British Medical Journal on Thursday.

TOP FIVE COUNTRIES FOR LIVING LONGER

WOMEN

1. Japan 87.2 yrs

2. Spain 85.8 yrs

3. Switzerland 85.4 yrs

4. France 85.5 yrs

5. Australia 85.46 yrs

MEN

1.Switzerland 81.6 yrs

2. Australia 81.5 yrs

3. Japan 81.01 yrs

4.Norway 80.61 yrs

5.Sweden 80.57 yrs

Australian Associated Press