A study that followed more than 15,000 people has found that those who reported watching television the most often had the greatest risk for blood clots in their veins compared with those who infrequently or never watched television.
The new findings are to feature at the American Heart Association's (AHA) Scientific Sessions 2017, held this week in Anaheim, CA.
Researchers have already linked the amount of time spent watching TV to risk of heart disease that develops from blood clots in arteries.
The study is significant as it is the first to explore the link between venous thromboembolism — that is, a range of conditions in which blood clots develop in veins — and TV viewing in a large group of people in a western population.
Venous thromboembolism (VTE) is an umbrella term that includes both deep vein thrombosis (DVT) and pulmonary embolism (PE). Although it can occur at any age, VTE is more common in people aged 60 and older.
DVTs are blood clots that form in veins deep inside the body, such as in the arms, legs, and pelvis. A PE develops when a clot breaks away and gets into the arteries of the lungs.
VTE is a major and growing public health concern in the United States, where it is thought to affect between 300,000 and 600,000 people per year. It is the most commonly diagnosed vascular condition, following strokes and heart attacks.
Despite exercise, TV viewing tied to VTEs
For the new study, Mary Cushman — a professor of medicine in the Larner College of Medicine at the University of Vermont in Burlington — and other investigators used data from the Atherosclerosis Risk in Communities Study.
The data came from 15,158 people aged 45–64, all of whom were free of VTE between 1987 and 1989 when they first reported which category their TV viewing frequency fell into, and these were "never or seldom," "sometimes," "often," or "very often." Updates on the categories were collected in 1993–1995 and 2009–2011, and VTE events were also noted during the follow-up period.
Over a follow-up period of 299,767 person-years — during which they identified 691 VTEs — they found that there was a "dose-response" relation between frequency of TV viewing and risk for developing a first VTE.
They found that the risk for VTE was 1.7 times higher in the participants who said that they watched TV "very often," compared with those who said that they watched it "never or seldom."
Even those whose level of physical activity met recommended guidelines had a 1.8 times higher risk for VTE if their reported TV viewing fell into the "very often" category, compared with those who reported "never or seldom."
Obesity was found to be more common in those participants who watched more TV, but the team said that its analysis showed that it only accounted for 25 percent of the higher risk of VTE.
They also found that the link between more TV viewing and VTE was equally strong for DVTs and PEs.
'Avoid prolonged sitting'
In 2016, the AHA issued a statement about the health risks of prolonged sitting. Its authors advise that sitting for long periods — even in people who are physically active — can raise the risk of diabetes, heart disease, and other persistent health problems.
Prof. Cushman suggests that people think about how they might keep moving to counteract the effect of prolonged TV viewing.
"You could put a treadmill or stationary bike in front of your TV and move while watching," she suggests, adding, "Or you can delay watching TV by 30 minutes while you take a walk."
"Watching TV itself isn't likely bad, but we tend to snack and sit still for prolonged periods while watching."
Prof. Mary Cushman