LONDON (CBS/AP) — Are you sitting down? In that case, you should probably stand up before reading this.

In the first advice of its kind, British experts are recommending office workers stand for at least two hours a day, in a warning against the dangers of prolonged sitting.

READ MORE: UPDATE: Cal Fire Crews Reach 80% Containment on Fremont Fire Near Napa-Sonoma County Line

The guidelines were developed by a group of experts invited by Public Health England and an advocacy group and were published online Monday in the British Journal of Sports Medicine.

The experts recommend people start with two hours of standing or light activity, adding they should eventually double that to four hours.

ALSO READ: Forget Your Standing Desk, Hamster-Wheel Is The New Workplace Health Trend

In recent years, the hazards of sitting too much have been compared to those of smoking, with research suggesting people who spend most of their days seated are more likely to be fat, have heart problems, cancer and even die earlier.

Not even regular exercise seems to help.

“Even if you’re meeting your physical activity guidelines, you cannot undo the risks of prolonged sitting,” said Gavin Bradley, director of the campaign group Get Britain Standing, one of the authors of the new guidance. Bradley, who spoke during a telephone interview while walking, said officials estimate the average Briton sitsfor more than half of their working hours. His group is expanding its campaign to other countries including the U.S. on Tuesday and is pushing for more people to have access to a desk that allows them to stand.

READ MORE: San Jose Leaders Announce Plan To Cut Homelessness With Emergency Housing, Jobs

According to the guidelines, people who sit the most have more than twice the risk of developing Type 2 diabetes and cardiovascular disease, a 13 percent increased risk of cancer and a 17 percent increased risk of premature death, compared to those who sit the least.

Jenny Nissler, an occupational physical therapist and spokeswoman for Britain’s Chartered Society of Physiotherapists, said people who sit for long stretches could be more prone to joint stiffness and back pain.

RELATED: Apple CEO Tim Cook Says ‘Sitting Is The New Cancer,’ Plugs Health Features Of New Smartwatch

“Companies should reconsider the culture around taking regular breaks and think about whether meetings could be held standing up or walking,” she said.

Bradley, who takes all his calls standing, says curbing the amount of time people spend sitting could have huge benefits, since up to 95 percent of adults in developed countries are classified as inactive.

“We’ve sat on this problem for far too long,” he said.

MORE NEWS: A's Drop 3rd In A Row To Mariners, Lose Ground In Race For Second AL Wild Card

© Copyright 2015 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.