What is it about sitting? Dunlop can't say for sure, but said experts think that sitting for an extended period causes muscles to burn less fat and blood to flow more sluggishly. Idle muscles and sluggish blood flow can contribute to high blood pressure, heart disease, swollen ankles and diabetes.
Dunlop's study found a link, not a cause-and-effect relationship.
The connection may actually go the other way, said Andrea LaCroix, a professor of epidemiology in family and preventive medicine and director of the Women's Health Center of Excellence at the University of California, San Diego School of Medicine. She recently found a link in her own study between higher amounts of sedentary time and higher risk of death in older women.
In the new study, however, the disability may be driving the inactivity, she said. "The more disabled people are, the more sedentary, because they are unable to exercise," LaCroix said.
Among the study's limitations, she noted, was that it looks only at a snapshot in time -- four days of tracking over a few years. A better approach would be to follow people over time and see if being sedentary leads to disability, said LaCroix, who is also an affiliate investigator at the Fred Hutchinson Cancer Research Center, in Seattle.
The take-home message, study author Dunlop said, is that older adults, regardless of how much they exercise, should decrease their sedentary behaviors. So, she's still encouraging exercise. But if that's difficult, decreasing sitting time is another goal.
How to do that? Stand up when you talk on the phone, she suggested. Park in a far-away space at the mall or market when you shop. At work or home, walk around a bit when you get up for coffee or water, she advised. Walk to nearby errands instead of taking the car. If you're able, take stairs, not elevators. You can use a pedometer to track your activity.