Australians who spent a lot of time sitting at a desk or in front of a TV had higher all-cause mortality in a three-year study than those who were only sedentary a few hours a day.
Researchers found that the link between too much time sitting and shortened lives persisted when they accounted for how much moderate or vigorous exercise people got as well as their weight and other measures of health.
The results suggest that shifting some time from sitting to light physical activity – such as slow walking and active chores – might have important long-term benefits, researchers said.
"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," Dr Hidde van der Ploeg, the new study's lead author from the University of Sydney, told Reuters Health in an email.
Reclining bad for your health
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% more likely to die during the study than those who sat less than four hours daily.
That doesn't prove sitting, itself, cuts people's lives short, she pointed out. Although participants reported on a variety of lifestyle habits, there could be other unmeasured differences between people who spend a lot or a little time sitting each day.
Still, the findings are consistent with other recent studies suggesting health consequences from too much sitting, said Dr 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 research.
Physical activity not insurance
People tend to think they're okay as long as they get their "dose" of working out each day, he said.
But, "Getting your 30 minutes of physical activity five times a week is not insurance against chronic disease," Dr Tremblay added. Instead, time spent doing moderate or vigorous exercise and time being totally sedentary may each affect long-term disease risks separately, he said.
For the new study, Dr van der Ploeg and her colleagues surveyed roughly 220,000 people from New South Wales, Australia between 2006 and 2008 and then tracked them using Australian mortality records for an average of almost three years.
They found that the extra mortality risk tied to sitting held up regardless of whether people were normal weight or overweight, how much time they spent exercising and whether they were healthy or had pre-existing medical conditions, according to a report March 26 in the Archives of Internal Medicine.
Interrupt sedentary behaviour
Dr van der Ploeg said too much sitting may affect blood vessels and metabolism by increasing fats in the blood and lowering HDL 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. "When you are sitting this is not happening because the muscles are not active."
Even for people who have jobs that involve a lot of desk work, there are ways to train you to regularly interrupt sedentary behaviour, Dr Tremblay said.
Have a stand up meeting
"Make sure the fax machine is four steps away from you, not within reaching distance," he advised. "Drink enough water that you have to pee four times a day. Stand up, stretch, walk around a little bit, say hi to your friend in the cubicle next door."
"Try standing up while on the phone or have a stand up meeting," Dr van der Ploeg suggested.
When it comes to life outside of work, "You don't have to stand or walk for 100% of your leisure time of course, as sitting is very comfortable," she said. "But try to find a healthy balance between sitting, standing and walking or other physical activities."
(Genevra Pittman, Reuters Health, March 2012)
Just how dangerous is sitting all day
Your plan for physical activity