Sitzfleisch can kill you, apparently. Researchers in New Zealand who studied hospital patients admitted for DVT (or deep vein thrombosis) discovered that 34 percent "were office workers who spent long periods of time seated at their desks." In contrast, only 21 percent had been passengers on long-distance flights. That is quite the trick, considering that almost any flight arriving in New Zealand is likely to be long-distance. The office workers with DVT had sat at their desks or computers "for a total of 14 hours a day and went for stretches of three to four hours without getting up from their chairs."

Deep vein thrombosis is a condition in which a blood clot forms in a vein deep in the body, most often in the legs. These clots become particularly dangerous when they move up the bloodstream into the lungs, heart or brain, where they can cause heart attacks, strokes and pulmonary embolisms. The best advice I've heard for avoiding DVT on long flights is to pop one or two aspirin before boarding the plane. I do that every morning before going to the office. Maybe you should, too. Going out for a long walk at noon might be a good thing as well. Oh - I forgot. You can't take breaks or work shorter hours. Due to all the downsizings at your firm in the last few years, you and your colleagues are short-staffed and overworked, led by management to believe that you will lose your job too if you don't work insane hours with no overtime. Ah, well. I guess you'll just have to kiss your health good-bye to keep those paychecks coming in. Sorry I brought the whole thing up...

"Long Hours at Desk Raise DVT Risk: Study" from MSN.com
"Office workers 'risk blood clots'" from BBC News