This one thing may derail your shot at healthy aging, scientists say

Before you settle in to binge the new season of “The Bear” or watch Team USA go for the gold at the Paris Olympics, think twice about the amount of time you spend on the couch in front of the TV. Your future self may thank you.

A new study by Harvard researchers links the popular pastime of sitting and watching television to the likelihood of reaching one's senior years in a state of good health: the more time spent doing the former, the lower the odds of achieving the latter.

The problem doesn't seem to be with sitting in general. After controlling for a variety of risk factors such as diet quality and smoking history, the researchers found no relationship between time spent in a chair at work and the chances of aging well. Ditto for sitting in cars or at home doing something besides watching TV, such as reading, eating meals or paying bills.

Yet for every additional two hours spent in front of the boob tube, a person's chance of meeting the researchers' definition of healthy aging declined by 12%, according to their study published this week in JAMA Network Open.

That does not bode well for the United States, where 62% of adults between the ages of 20 and 64 say they watch TV for at least two hours a day, as do 84% of senior citizens.

Read more: Even for the active, a long sit shortens life and erodes health

The findings are based on data from more than 45,000 women who participated in the Nurses Health Study. All of them were at least 50 years old and had no major chronic diseases back in 1992, when they answered a slew of questions about their health and what they did all day.

For instance, the nurses were asked how much time they spent standing or walking around at work or at home. They were asked about various types of exercise, including jogging, swimming laps, playing tennis and doing yoga. They were asked whether they mowed their own lawns.

And they were asked how many hours they spent doing all kinds of sitting.

A couple watches a movie on TV at their home in Norwalk while sharing a bowl of popcorn.
A couple watches a movie on TV at their home in Norwalk while sharing a bowl of popcorn. (Francine Orr / Los Angeles Times)

You might not be surprised to learn that the most popular type of sitting was while watching television. More than half of the women — 53% — said they watched between six and 20 hours of TV a week. (The median among this group was around 15.4 hours per week.) An additional 15% of the women said they watched between 21 and 40 hours of TV each week, and 2% watched even more.

The nurses were tracked for 20 years or until they died, whichever came first. By the end of the study period, 41% of them were still free of 11 major health conditions, including cancer, diabetes, heart failure, chronic obstructive pulmonary disease and multiple sclerosis. In addition, 44% of the nurses were in good mental health, 52% had no memory impairments and 16% had no physical impairments.

Only 8.6% of the women met all four of those criteria, which was what it took to achieve healthy aging.

On the whole, the women who watched more TV tended to be older, were more likely to be smokers or drinkers, consumed more calories and had higher body mass index scores than women who watched less TV. The more devoted TV watchers were also more likely to have high blood pressure and high cholesterol.

Read more: Get up at least once every 30 minutes. Failure to do so may shorten your life, study finds

Once the researchers accounted for these and a host of other differences, they found that the women who spent an hour or less each week sitting in front of the TV were the most likely to achieve healthy aging. Compared to them, women who watched TV for two to five hours per week were 9% less likely to be healthy agers; those who watched for six to 20 hours per week were 19% less likely; those who watched for 21 to 40 hours per week were 40% less likely; and those who watched for at least 41 hours a week were 45% less likely.

The researchers also found that replacing TV time with pretty much anything else — including sleep, for women who got no more than seven hours of shut-eye per night — would increase their odds of healthy aging. The more vigorous the new activity, the bigger the boost.

Although the actual percentage of women who succeeded in healthy aging was low, the study authors estimated that an additional 61% of the women could have joined that rarefied group if they had done four things:

  • Spent at least three hours per day engaged in light physical activity at work.

  • Invested at least 30 minutes a day in moderate to vigorous physical activity.

  • Kept their weight in the normal range instead of being overweight or obese.

  • Limited their TV-watching time to less than three hours a day.

The study didn't show that excess TV time caused any of the nurses to miss out on healthy aging, only that there was a significant inverse correlation between the two. Still, there's good reason to suspect that their favorite sedentary behavior bore at least some of the responsibility.

Previous studies have linked prolonged sitting — especially while watching television — to a variety of health problems, including diseases such as breast cancer, colorectal cancer, type 2 diabetes, cardiovascular disease and early death. (That particular study found that compared to sitting for less than three hours a day, sitting for at least twice that long was associated with a 17% increased risk of premature death for men and a 34% increased risk of premature death for women.)

Read more: Too much sitting may thin the part of your brain that's important for memory, study suggests

But the researchers from Harvard's T.H. Chan School of Public Health have taken things a step further, said Dr. I-Min Lee, an epidemiologist at Brigham & Women’s Hospital in Boston who studies how physical activity can prevent chronic diseases and extend life.

"This study expands what we know because it looked at 'healthy aging,'" said Lee, who was not involved in the study. "'Health' is not just the absence of disease; it includes dimensions of physical and mental health, function and well-being."

All of the study subjects were women, but the biological mechanisms are likely to apply to men as well, Lee said. Even so, it would be good to actually test this relationship in men, as well as in people from a wider range of racial and ethnic backgrounds, she said. (The group of women in the original Nurses Health Study was overwhelmingly white.)

The youngest of the Baby Boomers are now turning 60, and the proportion of the U.S. population that's at least 65 is projected to increase from roughly 17% today to nearly 21% in 2050, according to the U.S. Census Bureau.

"Population aging is an important public health issue," the study authors wrote, and strategies to promote healthy aging "are urgently needed."

This story originally appeared in Los Angeles Times.