New Australian research shows that no matter how physically active you are, your chances of dying before your time are increased by sitting for long periods.

And the more you sit, the greater the risk.

Those reporting the highest amount of daily sitting had a 48 per cent increased risk of premature death compared with those who sat for less than four hours a day, the research found.

This was independent of how much time they spent on physical activity.

The finding has come from the 45 and Up Study, which included more than 200,000 men and women in New South Wales in what researchers claim is the longest ongoing study in the Southern Hemisphere.

The study was set up to study healthy aging, and is managed by the Sax Institute in collaboration with the Cancer Council, the National Heart Foundation and NSW health agencies.

The Sax Institute is a coalition of 35 universities, public health and health service research groups.

Study co-author Professor Adrian Bauman, from the University of Sydney's school of public health, said the findings had important implications for public health programmes.

"They show that physical activity, while important, is no 'get out of jail free' card," he said.

Prof Bauman said programmes of the future might need to focus specifically on reducing prolonged periods of sitting as well as boosting the amount of exercise people undertook.

Earlier findings from the study had shown strong links between sedentary time and obesity.

But until now there had been limited evidence about the impact of sitting time on mortality risk.

Further work will be continued in a five-year follow-up study of 265,000 people enrolled in the research programme.