Here's a warning from health experts: Sitting is deadly. Scientists are increasingly warning that sitting for prolonged 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.

Research is preliminary, but 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 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 genes¹ regulating the amount of glucose² and fat in the body start to shut down.

Even for people who exercise, spending long stretches 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 bout³.

That wasn't welcome news for Aytekin Can, 31, who works at a London financial company, and spends most of his days sitting in front of a computer. Several evenings a week, Can also teaches jiu jitsu, a Japanese martial⁴ art involving wrestling, and also does Thai boxing.

"I'm sure there are some detrimental⁵ effects of staying still for too long, but I hope that being active when I can helps," he said. "I wouldn't want to think the sitting could be that dangerous."

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, independently of whether or not they exercised.

Figures from a US 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 offset⁶ 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. "Don't just send your colleague an e-mail. Walk over and talk to him. Standing⁷ up."

健康专家发出警告：久坐会致命。越来越多的科学家提醒，即使经常锻炼身体，长时间坐着也会对健康产生有害影响。而且不管你坐在哪里——办公室、学校、车上或是电脑、电视前——重要的是你坐着的时间。

目前该研究尚处于初步阶段，但已有几项研究显示，每天大部分时间都处于静坐状态的人更容易发胖、患心脏病甚至死亡。

瑞典体育及健康科学学院的艾琳•艾克布洛姆-巴克上周在英国《运动医学》杂志上发表的一篇评论文章中建议，相关机构应重新考虑如何界定身体锻炼，以强调久坐的危害。

尽管卫生官员已发布指南建议人们的最低身体活动量，但在一天最多坐几个小时的问题上还是个空白。

艾克布洛姆-巴克说：“在坐了四个小时后，身体会开始发出有害信号。”她解释说，此时调节体内葡萄糖和脂肪量的基因会开始罢工。

即使对那些经常锻炼的人来说，长时间坐着也有害。世界卫生组织的身体锻炼专家蒂姆•阿姆斯特朗说，对于那些每天锻炼但依然有很多时间是处于静坐状态的人来说，如果每天的锻炼可分散进行而不是一次集中完成，效果会更好。

这对于在伦敦一家金融公司工作的31岁的艾特金•肯来说不是什么好消息。肯每天大部分时间都坐在电脑前。不过他每周有几个晚上教授柔术（日本的一种摔跤武术），此外还练泰国拳击。

他说：“我知道长时间坐着不动肯定有害，但我希望我做的这些运动能起到作用。我不愿相信坐着会产生这么危险的后果。”

去年公布的一项研究发现，长时间坐着的人死亡率更高，无论他们是否从事身体锻炼。这项研究在12年内共对超过1.7万名加拿大人进行了跟踪调查。

美国2003年至2004年的一项调查数据显示，美国人每天有一半以上的时间处于静坐状态，无论是坐在办公桌前还是坐在车内。

专家称，还需要开展更多研究以测算每天坐多久会对健康产生威胁，以及怎样来消除这些有害影响。

艾克布洛姆-巴克说：“人们应该坚持锻炼，因为锻炼身体益处多多。但当他们在办公室时，应该尽可能多地起来活动活动。不要总是通过发电邮来与同事交流。可以走过去与他面谈。站着谈。”