"This is the first time we've shown sedentary behaviour was related to increased disability regardless of the amount of moderate exercise," said Dorothy Dunlop, professor of medicine at Northwestern University Feinberg School of Medicine and lead author of the study.
"Being sedentary is not just a synonym for inadequate physical activity," she added in a release.
The study in Wednesday's issue of the Journal of Physical Activity & Health looked at 2,286 adults aged 60 and older from the U.S. National Health and Nutrition Examination Survey. It compared people in similar health with the same amount of moderate vigorous activity, such as a brisk walking pace.
When participants wore accelerometers over seven days, the average time spent being sedentary during waking hours was almost nine hours. About 3.6 per cent reported "disabilities in activities of daily living" — difficulty or inability to get in and out of bed, eat, dress or walk that threaten personal independence. Other surveys also looked at bathing or toileting.
Despite the benefits of physical activity to promote health, the older adults spent almost two-thirds of their waking time being sedentary.
"Sedentary behaviour, such as sitting, is problematic and costly," the study's authors concluded. "A sedentary lifestyle has long been associated with premature mortality; recently this relationship was shown to be independent of moderate-to-vigorous activity."
Clinically, a sedentary lifestyle contributes to markers of poor health, the researchers said.
Replacing 30 minutes per day of sedentary time with equal amounts of light activity is associated with better physical health. To that end, the researchers suggested five ways to cut back on sitting time:- Stand up when you talk on the phone or during a work meeting.
- When you go to grocery store or mall, park in a space farthest away.
- When you get up to have glass of water, walk around the house or office.
- Walk for short errands instead of taking the car.
- Take the stairs instead of the elevator, if you are able.
Overall in the study, the odds of disability were 1.52 times greater for every one hour increase in sedentary time, independent of time spent in moderate-vigorous activity, the researchers found.
While the data was only examined at one point in time, it does corroborate animal studies suggesting immobility is a separate risk factor for ill health.
Other teams have shown that objectively measured sedentary time is related to metabolic syndrome, depression, cancer and mortality.