It is the first time life expectancy figures have cracked the 85 mark for an Australian state or territory population, with the 85.1 years life expectancy an increase on the previous year's 84.8.

The statistics show boys born in the capital now have a life expectancy of 81.2, leading the nation in the male category.

Hal Kendig of the Centre for Research on Aging, Health and Wellbeing at ANU said the explanation comes down to socio-economic factors.

"By and large, the population in Canberra has higher income, has more white collar sorts of jobs and is better educated, and all these socio-economic factors are associated with longer life expectancy," he said.

"The question is why does the socio-economic factor make a difference. It has a lot to do with the kind of lifestyles we live, what stress we're under, how much choice we have in our lives.

"The other factor would be we know in rural areas there are higher incidences of injuries, there are less healthy ways of living … and the ACT is basically a middle-sized city."

Heather Booth, associate professor of demography at ANU, said the Canberra environment is also enabling for healthy behaviour, further adding to the socio-economic factors. "All the bike paths, the walking, the clean air … being active is actually encouraged by the environment," she said.

Australia's national life expectancy at birth is among the highest in the world, with a combined male and female figure of 82 years - slightly lower than Japan and Hong Kong, but higher than Canada, New Zealand, Britain and the US.

While Professor Kendig suggests Australia's standard of healthcare would be a factor when comparing life expectancy internationally, it is unlikely to account for the ACT's higher figures. "You'd be hard pressed to argue healthcare in Canberra [is better than the rest of the country] … I don't think that's a major factor here."

The ACT has the third lowest infant mortality rate in the country at 2.9 deaths per 1000 live births, a statistic beaten by Western Australia (2.5) and Victoria (2.8).

But when it comes to the overall death rate, the ACT had the lowest in the country at 4.9 deaths per 1000 standard population last year, which is reflected by the high life expectancy.

"It used to be we had lots of babies and young mothers dying early in the lifespan, but that has largely been addressed, so what we're finding now is the increase in life expectancy is due to decreased death rates in middle and older age," Professor Kendig said.

"We're increasing the proportion of people who approach maximum life expectancy, so these figures show that if you're aged 65 and a woman, you're odds on to live into your 90s."

Nationally, the standardised death rate is the lowest ever recorded in Australia at 5.5 deaths per 1000 people.

It is down from 6.8 deaths per 1000 in 2002, with the decrease greater for males (two deaths/1000) than females (one death/1000).

"It's despite an increase of obesity, it's despite a number of other factors … even though we hear of all these health problems, overall life is getting longer," Professor Kendig said.