How long is too long to sit at your desk?

You may want to stand up while you read this.

The average office worker sits about 10 hours a day.

There are all those hours in front of the computer, plowing through emails, making calls or writing proposals — and eating lunch. And then there are hours sitting in front of the TV or surfing the Web at home.

Medical researchers have long warned that prolonged sitting is dangerous, associated with a significantly higher risk of heart disease, diabetes, obesity, cancer and depression, as well as muscle and joint problems.

Some have gone on to say that the office chair is worse for your health than smoking and kills more people than HIV. Even working out vigorously before or after work may not compensate for extending sitting.

But now those researchers have come up with suggestions for how much time to sit and to stand that could dramatically change our work habits.

According to the expert statement released in the British Journal of Sports Medicine, Americans should begin to stand, move and take breaks for at least two out of eight hours at work. Then Americans should gradually work up to spending at least half of your eight-hour work day in what researchers call these “light-intensity activities.”

“Our whole culture invites you to take a seat. We say, ‘Are you comfortable? Please take a seat?' So we know we have a huge job in front of us,” said Gavin Bradley, director of Active Working, an international group aimed at reducing excessive sitting that, along with Public Health England, convened the expert panel. “Our first order of business is to get people to spend two hours of their work day NOT sitting. However you do it, the point is to just get off your rear end.”

Bradley said the first level of activity is simply standing.

“I'm standing right now while I'm talking on the phone,” he said.

While the group endorses the use of sit/stand desks, Bradley said there are other activities that can get people to move for two hours during the work day.

“Taking your calls standing. Walking around. Pacing. Holding standing meetings. Walking meetings. Walking over to a colleague's desk instead of sending an email. Using the stairs instead of the elevator. Taking a lunch break. Simple stuff.”

Bradley himself has changed the way he works completely since taking on this challenge to get people out of their seats: He starts his day standing on a comfort mat and has his sit/stand desk programmed to tell him, through a pop up notification on his computer, to change his posture every 20 to 30 minutes.

“It's all about mixing it up,” he said. “Metabolism slows down 90 percent after 30 minutes of sitting. The enzymes that move the bad fat from your arteries to your muscles, where it can get burned off, slow down. The muscles in your lower body are turned off. And after two hours, good cholesterol drops 20 percent. Just getting up for five minutes is going to get things going again. These things are so simple they're almost stupid.”

Researchers have known about the link between inactivity and higher rates of sickness and mortality dating back to studies of bus drivers and office-based postal workers in the 1950s.

And more recent observational studies comparing workers who sit for long periods against those who sit for fewer hours have found that sedentary workers have more than twice the risk of developing Type 2 diabetes and cardiovascular disease, a 13 percent increased risk of cancer and 17 percent increased risk of dying.

At the same time, with the rise of office work, the use of cars and buses rather than walking or bicycles, and the rise of leisure pursuits like TV and computer games that favor the couch potato, the world has become more sedentary. The World Health Organization estimates that 95 percent of the world's adult population is inactive, failing to meet minimum recommendations for health of 30 minutes of moderate to intense physical activity five times a week.

Authors of the new guidelines said they are a starting point only, and designed to give people some kind of research-based target, rather than rely on the claims made by the manufacturers of treadmill and sit-stand desks that are becoming all the rage. (More than 90 percent of workers in Scandinavia have access to them.)

“This is an initial guidance, which we do expect to have to evolve with time,” said James Buckley, one of the report authors and a professor at the Institute of Medicine at the University Centre Shrewsbury and University of Chester. “But to ensure the marketing and promotions people to race away with self-determined claims, we have felt it is better to have some guidance rather than no guidance that is somehow linked with scientific evidence.”

James Levine, an obesity expert at the Mayo Clinic and author of the book, “Stand Up,” though not involved in the guidelines, said they were a good start. In his work, he found that the reason why some people seem to eat a lot, never work out, yet never put on weight, is because they're standing, walking and moving more throughout the day, rather than sitting for hours on end.

“(The guidelines) show we need to fundamentally rethink the way we're working,” Levine said. Some small studies, he said, have found not only health improved, but productivity ticked up 15 percent when people stood and moved more during the day. “The way we have developed our workplaces and even our schools is actually profoundly unhealthy. It's a real design failure.”