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　　More and more people sit for a long time every day．But experts are increasingly warning that it could be bad for their health．And it doesn't matter where the sitting takes place－at the office, in the car or before a computer or TV－just the overall number of hours it occurs．Several studies suggest people who spend most of their days sitting are more likely to be fat, have a heart attack or even die．

　　Elin Ekblom-Bak of the Swedish School of Sport and Health Sciences suggested that health officials rethink how they define physical activity to highlight the dangers of sitting．While health officials have issued guidelines recommending minimum amounts of physical activity, they haven't sggested people try to limit how much time they spend in a seated position．"After four hours of sitting, the body starts to send harmful signals，" Ekblom-Bak said．

　　However, some people argued that if they spent long stretches of time sitting but used their spare time to exercise, everything would be OK．Tim Armstrong, a physical activity expert, didn't agree and said they might get more benefit if that exercise was spread across the day, rather than in a single activity．

　　In a study that tracked more than 17,000 Canadians, researchers found people who sat more had a higher death risk, whether or not they exercised．"We don't have enough evidence yet to say how much sitting is bad，" said Peter Katzmarzyk who led the Canadian study．"But it seems the more you can get up and interrupt this seated behavior, the better．"

　　Figures from a US survey found Americans spend more than half their time sitting, from working at their desks to sitting in cars．"People should keep exercising because that has a lot of benefit，" Ekblom-Bak said．"But when they're in the office, they should try to interrupt sitting as often as possible，" she said．