The more time you spend watching television, the greater your risk may be for blood clots, according to a new study — even if you get plenty of exercise. The research underscores the dangers of sitting too long, the authors say, and suggests that getting the recommended amount of physical activity may not be enough to counteract its risks.
The new study was presented this week at the American Heart Association’s Scientific Sessions in Anaheim, California, and has not yet been published in a peer-reviewed medical journal.
To investigate the connection between television viewing and blood clots in the legs, arms, pelvis and lungs—a condition known as venous thromboembolism (VTE) — researchers from the University of Vermont examined data from more than 15,000 middle-age people who answered questions about their TV habits three times over about 20 years. During that time, doctors diagnosed 691 blood clots, or VTE events, in the group. (No one had blood clots at the start of the study.)
People who said they watched TV “very often” were 71% more likely to have developed a blood clot, compared to those who “never or seldom” watched. Among those who did the recommended 150 minutes of weekly physical activity, the disparity was even greater: Those who watched TV very often were 80% more likely to have had a blood clot than those who rarely or never did.
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The link between TV viewing and blood clots could be partially explained by obesity, say the researchers. Sitting more and moving less can lead to weight gain, they say, and excess weight is a risk factor for blood clots. But adjustments in the analysis found that obesity could only account for about 25% of the increased risk, suggesting that other factors also play a role.
Most blood clots due to inactivity occur in the legs, says study author Dr. Mary Cushman, director of the Thrombosis and Hemostasis Program at the University of Vermont Medical Center. “The veins are bringing blood back to the heart, so the blood has to go back up the legs against gravity,” she says. “When the blood is in a slow-flow state and the muscles aren’t working to keep it moving, it’s easy to see how clots can form.”
This happens most commonly when a person’s legs are immobilized because of trauma (in a cast after an injury, for example). But it can also occur during long periods of sitting in one position, which often goes along with TV viewing — especially in the age of streaming services available for binge-watching.
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Previous research has also linked prolonged television viewing to heart disease, blocked arteries and dangerous blood clots. In this new study, TV viewing increased the risk for life-threatening clots both in the arms and legs (a condition called deep vein thrombosis) and in the lungs (known as pulmonary embolism).
Together, these two conditions affect between 300,000 and 600,000 people in the United States every year, making VTE the most common vascular diagnosis after heart attack and stroke. VTE is most common in people 60 and older, but it can occur at any age.
During prolonged sitting spells, it’s important to move around, says Cushman, and the study serves as a reminder that even physically fit people should avoid sitting in one position for too long.
“This is why we have mobile apps on our phones that tell us to get up and move around every hour or so if you’re sitting at work or on the couch,” says Cushman. “I advocate getting some of your physical activity while you watch TV, by walking on a treadmill or doing something else active to break up the long periods.”
Eating a wholesome diet and maintaining a healthy weight can also reduce a person’s risk of developing blood clots, Cushman adds. And for people who are at heightened risk due to pregnancy, a recent illness or injury or a previous clot, doctors can prescribe blood-thinning medication or recommend compression stockings.
“This is an extremely common disease, yet many people don’t know anything about it — even people who have multiple risk factors,” says Cushman. “It’s important we raise awareness about it, and about the things people can do to protect themselves.”