Some people can't stand working. Mark Ramirez works standing.

He is not a waiter or factory worker -- he is a team leader at AOL. Ramirez could, if he wanted, curl into the cushiest leather chair in the Staples catalog. No, thanks. He prefers to stand most of the day at a desk raised to above stomach level.

"I've got my knees bent, I feel totally alive," Ramirez said. "It feels more natural to stand. I wouldn't go back to sitting."

In the past few years, standing has become the new sitting for 10 percent of AOL employees at the firm's Dulles campus, part of a standing ovation among accountants, programmers, bureaucrats, telemarketers and other office workers across the nation. GeekDesk, a California company that sells $800 desks raised by electric motors, says sales will triple this year. It has sold standing desks to the Secret Service and the U.S. Geological Survey. Many firms and government agencies require standing setups in new contracts for office furniture.

Standers have various reasons for taking to their feet: it makes them feel more focused, prevents drowsiness, makes them feel like a general even if they just push paper. (Former defense secretary Donald H. Rumsfeld works standing up. So does novelist Philip Roth.) But unknown to them, a debate is percolating among ergonomics experts and public health researchers about whether all office workers should be encouraged to stand - to save lives.

In academic papers with titles such as, "Your Chair: Comfortable but Deadly," physicians point to surprising new research showing higher rates of diabetes, obesity, heart disease and even mortality among people who sit for long stretches. A study earlier this year in the American Journal of Epidemiology showed that among 123,000 adults followed over 14 years, those who sat more than six hours a day were at least 18 percent more likely to die than those who sat less than three hours a day.

"Every rock we turn over when it comes to sitting is stunning," said Marc Hamilton, a leading researcher on inactivity physiology at the Pennington Biomedical Research Center in Louisiana. "Sitting is hazardous. It's dangerous. We are on the cusp of a major revolution about what we think of as healthy behavior in the workplace." He calls sitting "the new smoking."

Not so fast, other experts say. Standing too much at work will cause more long-term back injuries - ask factory workers, they say. Incidences of varicose veins among women will increase. The heart will have to pump more. Alan Hedge, a noted ergonomics scholar at Cornell University, went so far as to call standing at work "one of the stupidest things one would ever want to do. This is the high heels of the furniture industry."

What everyone can agree on, though, is that we were not exactly built to sit. "We were built to stand, to move, to walk," said James Levine, a Mayo Clinic endocrinologist who is so fanatical about not sitting at work that he walks at 1 mph all day on a treadmill at his desk.

He's the author of that "Comfortable but Deadly" paper, and in it, he provides a remarkable history of how we became a nation of sitters. The short version is that hunter-gatherers became agriculturists, the industrial revolution moved us into factories and the technological revolution moved us behind desks. And here we are, pecking away. Today's offices run on so much data that for many workers, two computer monitors are standard issue.

"With creativity, a person can eat, work, reproduce, play, shop and sleep without taking a step," Levine wrote. "Once enticed to the chair, we were stuck. Work and home alike: we do it sitting."

But when we sit, researchers say, important biological processes take a nap. An enzyme that vacuums dangerous fat out of the bloodstream only works properly when a body is upright. Standing also seems to ward off deadly heart disease, burn calories, increase how well insulin lowers glucose and produce the good brand of cholesterol. Most of these processes occur - or don't - regardless of whether someone exercises. Human beings need to stand.