Sitting for long periods of time has been linked to increased risk of cardiovascular disease and early death, but a new study suggests that not all types of sitting are equally unhealthy.

The study, led by researchers at Columbia University Vagelos College of Physicians and Surgeons, found that leisure-time sitting (while watching TV)—but not sitting at work—was associated with a greater risk of heart disease and death among the study’s more than 3,500 participants. The study also found that moderate-to-vigorous exercise may reduce or eliminate the harmful effects of sedentary television watching.

“Our findings show that how you spend your time outside of work may matter more when it comes to heart health,” study author Keith M. Diaz, PhD, assistant professor of behavioral medicine at Columbia University Vagelos College of Physicians and Surgeonsand a certified exercise physiologist. “Even if you have a job that requires you to sit for long periods of time, replacing the time you spend sitting at home with strenuous exercise could reduce your risk of heart disease and death.” The study was published online today in the Journal of the American Heart Association.

Background

A growing body of research shows that people who are sedentary—especially those who sit for long, uninterrupted periods of time—have a higher risk of cardiovascular disease and death.

But most previous studies did not follow people over time, making it difficult to draw conclusions about the relationship between sedentary behavior and health risk. These studies have included mainly people of European descent rather than African Americans, a group that has a higher risk of heart disease compared with whites. Previous studies also measured physical activity using an activity monitor, which is unable to distinguish between different types of sedentary behavior.

What the study found

The new study followed 3,592 people, all African Americans, living in Jackson, MS, for almost 8.5 years. The participants reported how much time they typically spent sitting while watching TV and during work. They also reported how much time they spent exercising in their down time.

The participants who had logged the most TV-viewing hours (4 or more hours a day) had a 50% greater risk of cardiovascular events and death compared to those who watched the least amount of TV (less than 2 hours a day). In contrast, those who sat the most at work had the same health risks as those who sat the least.

Even for the most dedicated TV watchers, moderate to vigorous physical activity—such as walking briskly or doing aerobic exercise—reduced the risk of heart attacks, stroke, or death. No increased risk of heart attack, stroke, or death was seen in people who watched TV for 4 or more hours a day and engaged in 150 minutes or more of exercise a week.

Why does the type of sitting matter?

In a previous study, Diaz found that excessive sitting is linked to worse health outcomes, and even more so when sitting occurs in lengthy, uninterrupted bouts.

“It may be that most people tend to watch television for hours without moving, while most workers get up from their desk frequently,” Diaz says. “The combination of eating a large meal such as dinner and then sitting for hours could also be particularly harmful.”

“More research is needed, but it’s possible that just taking a short break from your TV time and going for a walk may be enough to offset the harm of leisure-time sitting,” adds Diaz. “Almost any type of exercise that gets you breathing harder and your heart beating faster may be beneficial.”

And although occupational sitting was less problematic, Diaz notes that the same approach to movement applies at work. “We recognize that it isn’t easy for some workers, like truck drivers, to take breaks from sitting, but everyone else should make a regular habit of getting up from their desks. For those who can’t, our findings show that what you do outside of work may be what really counts.”

The researchers suspect that the study's findings may be applicable to anyone who is sedentary, even though the study focused on African Americans.

What’s next

In future studies, Diaz will examine why TV watching may be the most harmful sedentary behavior and whether the timing of sedentary behavior around dinner time could be a contributing factor.

About the study

The study is titled, “Types of Sedentary Behavior and Risk of Cardiovascular Events and Mortality in African-Americans: The Jackson Heart Study.”

The other contributors are: Jeanette Garcia (University of Central Florida, Orlando, FL), Andrea T. Duran (CUIMC), Joseph E. Schwartz, (CUIMC and Stony Brook University, Stony Brook, NY), John N. Booth III (University of Alabama Birmingham, Birmingham, AL), Steven P. Hooker (Arizona State University, Phoenix, AZ), Joshua Z. Willey (CUIMC), Ying Kuen Cheung (CUIMC), Chorong Park (New York University School of Medicine, New York, NY), Stephen K. Williams (New York University School of Medicine), Mario Sims (University of Mississippi Medical Center, Jackson, MS), and Daichi Shimbo (CUIMC).

The Jackson Heart Study is supported by contracts from the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute on Minority Health and Health Disparities (HHSN268201300046C, HHSN268201300047C, HHSN268201300048C, HHSN268201300049C, and HHSN268201300050C). This work was also supported by NHLBI grants (R01-HL117323and K24-HL125704.

All of the authors declare no conflict of interest.