Jan. 10, 2011 -- Hours spent lounging in front of a computer or television may hurt the heart, a new study shows.
The study shows that adults who averaged more than two hours sitting in front of a television or computer screen that was not related to their job or schoolwork had roughly twice the risk of having heart attacks, heart surgeries, strokes, or other cardiovascular events, compared to those who logged less than two hours of daily screen time.
What’s more, the risk did not drop appreciably when researchers factored in other variables, like a history of diabetes or high blood pressure, smoking, body weight, socioeconomic or marital status, or even a regular exercise routine.
Public health experts and cardiologists say the study offers more proof that people may need to shift their wellness goals slightly, beyond simply making sure they get a daily workout to also reducing the amount of time they are sedentary.
“It’s not even about the exercise. It’s about not sitting,” says Suzanne Steinbaum, DO, a preventive cardiologist at Lenox Hill Hospital in New York City. “I think that sort of points us in a little different direction. In order for you not to cause harm to yourself, you really need to focus on getting up and moving.”
Heart Health Goes Down the Tubes
For the study, which is due to be published in the Jan. 18 issue of the Journal of the American College of Cardiology, researchers at University College London and the University of Queensland in Australia followed more than 4,500 adults who took part in the Scottish Health Survey.
Participants were over age 34 and were followed for an average of 4.3 years.
To figure out how much leisure time was spent sitting, researchers asked: “Thinking of weekdays, how much time, on average, do you spend watching TV or another type of screen such as a computer or video game? (Please do not include any time spent in front of a screen while at school, college or work.)”
Researchers also asked about physical activity both at work and outside of work, including any heavy housework like scrubbing floors, heavy gardening like digging, walking, and leisure time exercise, such as cycling, swimming, aerobics, dancing, and football.
They then linked the survey results to hospital data on admissions and deaths in Scotland from 1981 through December 2007.
Compared to people who spent less than two hours a day in front of a TV or computer, those who spent four hours a day on screen-based entertainment had a 48% risk of dying for any reason; those who spent more than two hours a day sitting in front of a screen had 125% greater risk of experiencing cardiovascular events like heart attacks and strokes.
Those risks remained even after scientists accounted for other things known to influence heart health, like high blood pressure, diabetes, socioeconomic and martial status, smoking and surprisingly, even regular exercise.
“It is all a matter of habit. Many of us have learned to go back home, turn the TV set on and sit down for several hours -- it’s convenient and easy to do. But doing so is bad for the heart and our health in general,” says Emmanuel Stamatakis, PhD, a senior research fellow in the department of epidemiology and public health, University College London, in a news release.
“And according to what we know so far, these health risks may not be mitigated by exercise, a finding that underscores the urgent need for public health recommendations to include guidelines for limiting recreational sitting and other sedentary behaviors, in addition to improving physical activity,” he says.
How Sitting Harms the Heart
Though previous studies have found the similar associations between time spent sitting and the risks for heart attacks and strokes, scientists still aren’t sure why being sedentary appears to be so bad for the body.
The current study, however, offers new clues.
Four factors, in particular, seemed to explain about one-quarter of the association between screen time and cardiovascular risks. Those were body mass index (BMI), total cholesterol, HDL “good” cholesterol levels, and C-reactive protein (CRP), which is a marker of low-grade inflammation.
In fact, CRP alone explained 18% of this association.
CRP levels were about 300% higher in people who reported spending at least four hours a day watching a screen compared with those spent less than two hours front of a TV or computer, suggesting that being sedentary may contribute to a kind of chronic, low-grade inflammation.
The study also notes that levels of a key enzyme that breaks down blood fats have been shown to drop by 80% to 90% during sitting, another mechanism that may contribute to heart risks.
“We know that with obesity for example, we know there’s an increase in CRP, and now we’re seeing that sitting has the same ability to elevate CRP,” Steinbaum says.
“As risk factors go, I think that makes it very compelling,” she says.