Lots of time sitting, and very little spent moving around, may contribute to loss of the ability to walk in old age, a large US study suggests.
Researchers found that older people who watched more than five hours of TV a day and were physically active for three hours or less each week were more likely than their more active peers to have developed trouble walking at the end of a 10-year follow-up.
Reducing sedentary time along with increasing physical activity may be necessary to maintain function in older age, the authors write in Journals of Gerontology: Medical Sciences.
"If you perform low-level physical activity, like less than three hours a week, and you sit, especially sit watching television more than five hours a day, your risk of mobility loss is over three times greater than people who report high levels of physical activity and very low levels of sitting," lead author Loretta DiPietro told Reuters Health in a phone interview.
"Now keep in mind, when I say physical activity, that doesn't mean going to the gym and working out necessarily. We combined all levels of light, moderate and vigorous activity. It's the whole volume," said DiPietro, a researcher at the George Washington University's Milken Institute School of Public Health in Washington, DC.
Walking, doing errands and moving about, housework, and walking the dog all count as physical activity, she said.
The researchers analysed data from the nationwide NIH-AARP Diet and Health Study, which began in 1995, when participants were between 50 and 71 years old and filled out questionnaires about their medical histories, diet and physical activity.
Roughly 10 years later, follow-up information was available for more than 134,000 participants who were healthy at baseline and answered another survey.
At the end of the study period, about 30 per cent of the participants reported having some degree of mobility disability, such as having difficulty walking at a speed greater than 2 miles per hour or not being able to walk at all.
People who were the most physically active at the beginning of the study period, defined as active more than 7 hours each week, and who sat for less than 6 hours per day, did not have any excess risk of mobility disability by the end of the study period.
Among the most active adults, even those who sat for more than 7 hours per day also had a lower risk of mobility disability than the least-active adults who were also less sedentary.
In all groups, as TV viewing time increased, so did the likelihood of a walking disability. People who watched five or more hours of TV per day at the start of the study period, for example, had a 65 per cent greater risk than those who watched the least TV of reporting a mobility disability by the end of the study.
"You know, what we've done in our culture is replace light-intensity activities with automation," DiPietro said. For instance, the internet means we don't need to go shopping anymore. "We can order from Amazon, we can order groceries, etc," she said. "We don't walk down the hallway anymore to talk to someone, we text them."
One strategy she and her colleagues propose is adding those things back. "Go down the hallway and talk. Climb up a flight of stairs to go talk to someone or to deliver something," she said.
"If you have to sit at a desk, every hour, you set a timer and you get up and you walk around." DiPietro also recommends using a standing desk at work or for computer time.
"If you're watching TV for extended periods of time, stand up during commercials, and march in place or walk around the house," she said.
This study adds encouraging evidence that as people spent more time being physically active, the lower the chance they experienced harmful effects from being sedentary," said Dorothy Dunlap, a researcher at Northwestern University Feinberg School of Medicine in Chicago who wasn't involved in the research.
Older adults who are physically active are less likely to develop serious conditions including heart disease, stroke, diabetes, high blood pressure and obesity, Dunlap said by email.
"People who are physically active are less likely to become depressed and are less likely to die prematurely," she added.