They found that replacing a sedentary behavior such as watching TV with even low-intensity activity — such as standing or walking around while cooking or washing clothes — increased one’s odds of healthy aging. And at work, replacing some of the time spent sitting with simple movements such as standing or walking around the office can improve health.
“These findings indicate that physical activity need not be high intensity to potentially benefit various aspects of health, which have especially important public health implications as older people tend to have limited physical ability to engage in moderate-to-vigorous physical activity,” Molin Wang, an associate professor in epidemiology at the Harvard T.H. Chan School of Public Health and an author of the study, wrote in an email.
For the purposes of the study, healthy aging was defined as surviving to at least 70 with no major chronic diseases, and no impairment in subjective memory, physical function or mental health. The data, though, suggests the relationship between light activity and healthy aging continues into the 80s and 90s, Wang said.
Replacing TV time with physical activity or sleep
Researchers used responses from a Nurses’ Health Study of 45,176 women that began more than 20 years ago. Respondents were asked questions such as “On average, how many hours per week do you spend standing or walking around at home?” or “On average, how many hours per week did you spend standing or walking around at work or away from home?” Participants had an average age of 59.2 and were free of major chronic diseases when the study began in 1992. They were then tracked for 20 years.
The study incorporated isotemporal substitution modeling to evaluate the potential effect on healthy aging of replacing one hour of one behavior with the equivalent duration of another. They found, for instance, that every two hours spent sitting and watching television was linked to a 12 percent decrease in the odds of healthy aging. Conversely, every two hours per day of light physical activity at work was linked to a 6 percent rise in the odds of healthy aging.
Replacing TV time with light physical activity at home increased one’s odds of healthy aging as well. For those who slept seven hours a night or less, replacing television time with sleep was also beneficial for health.
“What we found is that if you replace sedentary behaviors with any activities, I mean, even light physical activities, like standing or walking around, or doing household chores, it’s better than just being a couch potato for an extended period of time,” said Frank Hu, professor and chair of the Department of Nutrition at the Harvard T.H. Chan School of Public Health and an author of the study.
And swapping TV time for light physical activity, or sleep for some individuals, at any age would be beneficial, Wang said.
The researchers adjusted for several variables, including age; income; family history of cancer, myocardial infarction and diabetes; baseline hypertension and high cholesterol; menopausal status and postmenopausal hormone use; and diet.
The study findings show an association between sitting and watching television vs. light physical activity, and the odds of healthy aging, and not a causal relationship. The researchers also wrote that because their study population was limited to nurses in the United States, the “findings might not be generalizable to other populations.”
Hu said the isotemporal substitution model they used was important, likening it to the concept of opportunity cost in economic theory or the idea of isocaloric substitutions in food and nutrition. These models acknowledge that people have a finite amount of time in a day or a finite number of calories they are going to consume, so when they choose one thing over another, it comes at a cost of doing something else.
Watching TV and junk food consumption
The problem with watching TV is not just that it’s a sedentary habit. While watching, people tend to eat more junk food and drink more sugary beverages, increasing their caloric consumption, Hu said.
Scott Lear, a professor in health sciences at Simon Fraser University in Vancouver, said that while the findings of the study may not be groundbreaking, researchers made some important distinctions. They made clear that health is also affected by what people are doing when they’re sedentary and where they’re doing it — not just that they’re inactive. There are different health repercussions to sitting at home vs. at work and between sitting and watching TV as opposed to sitting and reading or writing.
“Watching TV has been associated with greater risk for early death, Type 2 diabetes, heart disease, and some cancers, and watching TV is a bit different than just, say, sitting reading a book,” said Lear, who was not involved in the study.
The fact that sleep was included in the study was also novel, Lear said, noting that it’s an underrated health behavior. It may seem like a sedentary behavior, but the brain is very active when we sleep, performing functions that affect our overall health.
He compared the brain to an office, and at the end of the day, all of the day’s happenings — going to the grocery store, having to run to the bus, talking to someone at work — are like files that have been scattered all over the floor and must be picked up and organized by morning. That’s what the brain does when we sleep, he said.
Sleep is also when we remove toxins that build up in the brain throughout the day, and studies have shown a link between an accumulation of this metabolic waste and a person’s risk for dementia later in life, Lear said.
“We talk about physical activity and healthy nutrition. Those tend to be the two heavyweights that we talk about. But sleep is incredibly important,” Lear said.
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