People who spent a lot of time sitting at a desk or in front of a television are more likely to die than those who are only sedentary a few hours a day, according to an Australian study that looked at death rates during a three-year period.
Researchers, whose results appeared in the Archives of Internal Medicine, found that the link between too much time sitting and shortened lives stuck even when they accounted for how much moderate or vigorous exercise people got, as well as their weight and other measures of health.
That suggests that shifting some time from sitting to light physical activity, such as slow walking or active chores, might have important long-term benefits, they added.
"When we give people messages about how much physical activity they should be doing, we also need to talk to them about reducing the amount of hours they spend sitting each day," said Hidde van der Ploeg, the new study's lead author from the University of Sydney.
The findings are consistent with other recent studies suggesting health consequences from too much sitting, said Mark Tremblay, an obesity and activity researcher at Children's Hospital of Eastern Ontario in Ottawa.
"Sitting or reclining, especially in front of screens, is bad for you regardless of your age," said Dr. Tremblay, who wasn't involved in the new study.
Both he and Dr. Van der Ploeg said there are ways that even people who have jobs involving a lot of desk work can train themselves to regularly interrupt sedentary behaviour, such as standing up while on the phone or holding a stand-up meeting.
"Make sure the fax machine is four steps away from you, not within reaching distance," Dr. Tremblay said.
"Stand up, stretch, walk around a little bit, say 'hi' to your friend in the cubicle next door."
He added that even though people tend to think they're okay as long as they work out a certain amount a day, that's not necessarily the case. "Getting your 30 minutes of physical activity five times a week is not insurance against chronic disease."
Of more than 200,000 adults age 45 and older, Dr. van der Ploeg and her colleagues found that people who reported sitting for at least 11 hours a day were 40 per cent more likely to die during the study than those who sat less than four hours daily.
That doesn't, however, prove that sitting itself cuts people's lives short, she noted, adding that there could be other unmeasured differences between people who spend a lot or a little time sitting each day.
The team surveyed about 220,000 people from New South Wales, Australia, between 2006 and 2008, including questions about participants' general health and any medical conditions they had, whether they smoked and how much time they spent both exercising and sitting each day.
Then the research team tracked responders using Australian mortality records for an average of almost three years, during which 5,400 – between 2 per cent and 3 per cent – died.
They found that the extra risk tied to sitting held up regardless of whether people were normal weight or overweight, how much time they spent working out and whether they were healthy or had pre-existing medical conditions.
Dr. Van der Ploeg said too much sitting may affect blood vessels and metabolism by increasing fats in the blood and lowering "good" cholesterol levels.
"When you are standing or walking, your leg muscles are constantly working which helps to clear blood glucose and blood fats from the blood stream," she said. "If you are sitting, this is not happening because the muscles are not active."