LONDON—Here's a new warning from health experts: Sitting is deadly.    
     Scientists are increasingly warning that sitting for prolonged(持续很久的)periods—even if you also
exercise regularly—could be bad for your health. And it doesn't matter where the sitting takes place—at
the office, at school, 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.    
     In an editorial published this week in the British Journal of Sports Medicine, Elin Ekblom-Bak of
the Swedish School of Sport and Health Sciences suggested that authorities rethink how they define
physical activity to highlight the dangers of sitting.    
     While health officials have issued guidelines recommending minimum (最少的) amounts of physical
activity, they haven’t suggested 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. She explained
that genes regulating (调节) the amount of glucose (葡萄糖) and fat in the body start to shut down.    
      Even for people who exercise, spending long periods of time sitting at a desk is still harmful. Tim
Armstrong, a physical activity expert at the World Health Organization, said people who exercise every
day—but still spend a lot of time sitting—might get more benefit if that exercise were spread across the
day, rather than in a single bout (一回).    
     Still, in a study published last year that tracked more than 17,000 Canadians for about a dozen years,
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 of the
Pennington Biomedical Research Center in Baton Rouge, who led the Canadian study. "But it seems the
more you can get up and interrupt this sedentary (坐着的) behavior, the better."  
     Figures from a U.S. survey in 2003-2004 found Americans spend more than half their time sitting,
from working at their desks to sitting in cars.  
     Experts said more research is needed to figure out just how much sitting is dangerous, and what might
be possible to offset those effects.    
     "People should keep exercising because that has a lot of benefits," Ekblom-Bak said. "But when
they're in the office, they should try to interrupt sitting as often as possible," she said.