Updated: March 31, 2018
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.
The Active Couch Potato Phenomena
If you get the recommended 150 minutes of moderate exercise per week, yet you sit at work for extended periods of time, you are what's called an "active couch potato." Professor Stuart Biddle, who led the national guidelines for Australia on reducing sitting, says people who take regular exercise may still be broadly sedentary.
"Even if you do a half an hour or an hour or of exercise every day doesn't give us the reassurance that sitting for the other 23 hours is ok. In fact, it's not," said Dr. David Alter of the Toronto Rehabilitation Institute, one of the authors of the 2013 study published in Annals of Internal Medicine, which is based on a review and analysis of previous research. It found that the health hazards seem to be greatest for people who sit 8 or 9 hours a day. The impact was even greater in people who didn't exercise regularly.
The study found that extended periods of sitting raised the risk of cardiovascular disease by 14%, cancer by 13%, and diabetes by 91%. Those who sat for long stretches and didn't exercise regularly had a 40% higher risk of early death. With regular exercise, the risk was about 10%.
The problem is that many people sit at work all day, and then sit at home in front of the TV, a tablet, or computer. One study cited by James A. Levine, M.D., Ph.D, one of the leaders of the movement to get people to stop sitting for extended periods, compared adults who spent less than 2 hours a day in front of the TV or any kind of screen with those who logged more than 4 hours a day of screen time. Those with greater screen time had:
- An almost 50% increased risk of death from any cause
- About a 125% increased risk of events associated with cardiovascular disease, such as a heart attack.
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.