“Replacing sedentary behaviors, like watching television, with low-intensity activities like standing and walking around while cooking or doing laundry can improve your chances of healthy aging. And at work, replacing some of your sitting time with simple movements like standing and walking around the office can improve your health.”
“These findings indicate that physical activity does not need to be vigorous in intensity to benefit multiple aspects of health, which has particularly important public health implications for older adults because they tend to have limited physical capacity for moderate-to-vigorous physical activity,” Morin Wang, an associate professor of epidemiology at the Harvard School of Public Health and study author, said in an email.
For the purposes of the study, healthy aging was defined as being free of major chronic diseases and unimpaired subjective memory, physical function or mental health, and living to at least age 70. But the data suggests that the relationship between light exercise and healthy aging may continue into one’s 80s and 90s, Wang said.
Replace TV time with exercise and sleep
The researchers used responses from the Nurses’ Health Study, which began more than 20 years ago and included 45,176 women. Respondents were asked questions such as, “On average, how many hours per week do you stand or walk around at home?” and “On average, how many hours per week do you stand or walk around outside of work or home?” When the study began in 1992, participants were on average 59.2 years old and had no major chronic illnesses. They were then followed for 20 years.
The study employed an isochronic substitution model to assess the potential impact of replacing one hour of one activity with an equivalent hour of another activity on healthy aging. For example, they found that for every two hours spent sitting and watching TV, the odds of healthy aging decreased by 12 percent. Conversely, they found that two hours a day of light physical activity during work increased the odds of healthy aging by 6 percent.
Replacing television time with light exercise at home may also improve your chances of healthy aging. For people who sleep fewer than seven hours a night, replacing television time with sleep may also have health benefits.
“Our results suggest that replacing sedentary behavior with light physical activity like standing, walking or doing household chores is better than long periods of lounging on the couch,” said Frank Hu, professor and chair of the Department of Nutrition at the Harvard School of Public Health and author of the study.
And replacing television time with light exercise or, in some cases, sleep, could be beneficial for people of all ages, Wang said.
The researchers adjusted for several variables, including age, income, family history of cancer, myocardial infarction, or diabetes, baseline high blood pressure and high cholesterol, menopausal status and postmenopausal hormone use, and diet.
Research shows there is a link between sitting down to watch TV and sitting down to watch TV. The researchers said there was a causal, but not causal, link between light physical activity and the odds of healthy aging, and they wrote that because the study was limited to U.S. nurses, “findings may not be generalizable to other populations.”
Hu said the isotemporal substitution model they used was key, likening it to the concept of opportunity cost in economic theory and the idea of isocaloric substitution in food and nutrition. These models acknowledge that people only have a limited amount of time in a day and calories they can consume, so choosing one thing over another incurs the cost of doing something else.
Watching TV and eating junk food
The problem with watching TV isn’t just that it’s a sedentary habit: People also tend to eat junk food and drink sugary drinks while watching TV, increasing their calorie intake, Hu said.
Scott Lear, a professor of health sciences at Simon Fraser University in Vancouver, said that while the findings may not be groundbreaking, the researchers did uncover some important differences. They found that health is affected not just by inactivity, but also by what you do when you sit and where you do it. Sitting at home has different health effects than sitting at work, and sitting watching TV has different health effects than sitting reading or writing.
“Watching television has been associated with an increased risk of early death, type 2 diabetes, heart disease and some cancers, and watching television is a little different from, say, just sitting down and reading a book,” said Lea, who was not involved in the study.
The inclusion of sleep in the study was also novel, Lea said, noting that it is an underappreciated health behavior: While it may seem like a sedentary behavior, during sleep the brain is highly active and carries out functions that impact overall health.
He likens the brain to an office, and at the end of the day, all the events of that day — your trip to the grocery store, your rush to catch the bus, your conversation with someone at work — are like files scattered all over the floor that have to be picked up and organized by morning. That’s what the brain does when we’re asleep, he said.
Sleep is also the time when the brain clears out toxins that build up throughout the day, and research has shown a link between this buildup of metabolic waste and the risk of dementia later in life, Lea said.
“We talk about physical activity and healthy nutrition, those are the two most important things we talk about, but sleep is super important,” Lear said.
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