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, Ph.D., assistant professor of behavioral medicine at Columbia University Vagelos College of Physicians and Surgeons and 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.
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, Miss., 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.
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.
The study is titled, “Types of Sedentary Behavior and Risk of Cardiovascular Events and Mortality in African-Americans: The Jackson Heart Study.”
According to the Center for Disease Control, heart disease (which includes coronary heart disease, heart attack, congestive heart failure, and congenital heart disease), is the leading cause of death for men and women in the U.S., with 611,105 deaths in 2013.
Until recently, prevention included not smoking, lowering cholesterol, reducing high blood pressure, keeping your weight under control, and doing moderate exercise 150 minutes per week. Many studies are confirming that there’s another factor, independent of exercise: how long someone spends sitting.
The first study done on sitting vs. standing is from the early 1950s that compared London bus drivers to more physically active bus conductors, and those who sat at a desk to postmen. The non-sedentary groups had lower rates of coronary heart disease as well as smaller uniform sizes (Morris JN, Heady JA, Raffle PAB et al (1953). Coronary heart disease and physical activity of work. Lancet 262(6796): 1109–1110.)
One of the biggest studies done on the dangers of extended periods of sitting was done by researchers from Loughborough University and the University of Leicester (a public research university in the UK) in 2011. It involved 800,000 people and found that those who sat the most, in comparison to those who sat the least, had:
- 112% increase in the risk of diabetes
- 147% increase in cardiovascular events
- 90% increase in death caused by cardiovascular events
- 49% increase in death from any cause
According to the American Heart Association, 20% of adults will be diagnosed with heart failure during their lifetime. African-Americans and Hispanics may have a greater risk than non-Hispanic whites, and men have a greater risk than women.
One study focused on the lifestyles of 84,170 men aged 45 to 69 and the incidence of heart failure over time. Researchers found that while vigorous exercise did reduce the risk of heart failure, low to moderate exercise had less of an impact on heart failure rates among men who also spent relatively long periods of time sitting.
Researchers found that men who spend 5 or more hours a day sitting were 34% more likely to develop heart failure than men who sit less than 2 hours a day outside work. Additionally, the increased risk linked to sitting was not eliminated by low to medium levels of physical activity. “Our results strengthen the developing position that too much sitting is detrimental to cardiovascular health, independent of regular physical activity,” authors wrote.
The National Institutes of Health conducted the Women’s Health Initiative Observational Study, which followed more than 93,600 women ages 50 to 79 years old for about 8 years. Researchers found that women who sat more than 10 hours per day were at a significantly higher risk of cardiovascular events, such as stroke, heart disease, or heart attack compared to the women who sat 5 hours per day or less.
But the group most at risk were the women who sat more than 10 hours per day and got little to no physical activity, especially those who were overweight and greater than 70 years old.
How Excessive Sitting Increases Your Chances of Cardiovascular Disease
How excessive sitting results in cardiovascular disease is not thoroughly understood. Professor Stuart Biddle, who has published over 250 research papers, 14 books, 70 book chapters and presented over 750 research papers at conferences, explains that our current understanding is heavily influenced by research on the effect of weightlessness on astronauts in the 1970s.
“Sitting for an extended period of time is thought to simulate, albeit to a lesser degree, the effects of weightlessness on astronauts,” says Professor Biddle. “Essentially, the body is ‘shutting down’ while sitting and there is little muscle activity.”
Excessive sitting slows the metabolism, burning approximately 50 fewer calories per hour than standing, which reduces your body’s ability to regulate blood sugar, blood pressure, and metabolize fat, as well as causing weaker muscles and bones.
Muscles burn less fat and blood flows more sluggishly during a long sit, allowing fatty acids to more easily clog the heart. Prolonged sitting has been linked to high blood pressure and elevated cholesterol, and people with the most sedentary time are more than twice as likely to have cardiovascular disease than those with the least.
According to the American Heart Association, there’s a theory that not using the muscles enough can lead to abnormal blood fat profiles through the suppression of an enzyme called lipoprotein lipase, which can convert “bad” cholesterol into good, among other functions.
Journal information: Journal of the American Heart Association
Provided by Columbia University Irving Medical Center