People stuck at their desks six hours a day should exercise for up to 40 minutes to mitigate the risks associated with sitting too much, new research suggests.

People with desk jobs have been urged to spend up to 40 minutes a day exercising to offset the health risks associated with sitting too much.

A University of Sydney study found about 20 to 40 minutes of daily physical activity is important for people who sit for longer than six hours a day.

The research, published on Tuesday, suggests reducing the amount of sitting time isn't enough to mitigate the risks of premature death and cardiovascular disease.

Professor Emmanuel Stamatakis said people who sit for more than eight hours a day and are not physically active have a 107 per cent higher risk of cardiovascular death compared to those who do least one hour of physical activity a day and sit less than four hours.

"Sitting time was associated consistently with both overall premature mortality and cardiovascular disease mortality in the least physically active groups," Professor Stamatakis said in a statement.

The research suggested 150 to 300 minutes of physical activity a week or 20 to 40 minutes a day could help eliminate the risks associated with long periods of sitting.

"Any movement is good for health but physical activity of moderate to vigorous intensity - that is activities that get people out of breath - is the most potent and most time-efficient," Professor Stamatakis said.

The research - published in the Journal of the American College of Cardiology - was conducted in collaboration with the Norwegian School of Sport Sciences, Norwegian Institute of Public Health and the UK's Loughborough University.