Does binge-watching TV increase the risk of “deadly blood clots”?

Watching TV for long periods has been linked with an increased higher risk of developing a venous thromboembolism (VTE). This is a condition where a blood clot forms in a vein. It includes deep vein thrombosis (DVT) and pulmonary embolism, which is when a clot travels to the lungs – which can be serious or even fatal.

These findings, published in the European Journal of Preventative Cardiology, used data from three previous studies, two from the USA and one from Japan. The three studies included 130,000 people in total. Two of them measured DVT and pulmonary embolism, but the largest study only looked at pulmonary embolism. They were asked how much time they spent watching TV, and were divided into ‘prolonged viewers’ and ‘seldom viewers’.

Researchers followed participants for up to 19 years afterwards. During the follow-up, 964 people developed a VTE, with the ‘prolonged viewers’ 1.35 times more likely (in other words, 35 per cent more likely) to develop it than ‘seldom viewers’. They found that even people who were physically active overall had an increase in risk.

We already know that spending a lot of time sitting down can increase your risk of blood clots and other health problems. DVT’s tend to form in the leg and are more likely to occur happen when you spend time sitting down. When you’re sitting, the blood flow in your leg slows down, so it is more likely to pool and start to clot. When you move your legs, the action of your calf muscles helps to squeeze the blood back up towards your heart.

The scientists mentioned that other research has found that exercise can reduce the risk of death in relation to time spent sitting sitting, but that exercise didn’t seem to reduce this risk as much in people who watch a lot of television.

They suggested that the increased risk of blood clots associated with TV watching could be due to sitting still in cramped positions for long periods of time, so taking frequent breaks to move around might be important to prevent blood clots. They speculated that the increased risk could also be due to unhealthy eating habits often associated with watching TV (an unhealthy diet can also increase your risk of blood clots).

How good was the research?

The three studies included in this research review followed a large number of people and adjusted for factors that can affect the risk of blood clots, including age, sex, weight and regular exercise. However, the largest of the three studies (86,000 people) only looked at pulmonary embolism. There were only 59 cases of pulmonary embolism in that study, which is a relatively small number from which to draw conclusions about difference in risk.

As the researchers themselves point out, since the studies used different ways to categorise how much television was watched, they were not able to investigate the exact relationship between watching TV and risk of developing blood clots. The press release that accompanies the research said that the “prolonged viewers” meant watching more than four hours a day, whilst “seldom” meant less than two and a half hours a day. However, one of the three studies measured how frequently people watched television, not how long for, so we need to be wary of drawing any firm conclusions about how much time watching TV might be considered risky.

The findings are observational – in other words, they do not prove that extended TV watching directly causes blood clots. 

How good was the media coverage?

The study was picked up by newspapers including The Sun and the Daily Mail.

The Daily Mail coverage was largely accurate and pointed out that “the findings are based on observational studies, so the increased risk among those who watched more television could be down to other factors, such as other lifestyle or health triggers.”

However, the Daily Mail story used a potentially misleading headline, saying “Binge-watching TV in middle-age may raise the risk of blood clots by a third.” The research included people up to 79 (so not just middle-aged people) and didn’t look at differences in risk between age groups. In general, risk of DVTs is known to increase with age.

The Sun article was much shorter, saying that “watching TV for four hours or more increases risk of deadly blood clots”. It included a statistic that “one in four Brits dies from clot-related conditions such as heart attacks or strokes” – two conditions that aren’t directly related to the type of clot the study mentions.

The BHF verdict

This research can’t tell us how much time watching television is “too much” in terms of your risk of DVT. But it does reinforce that sitting still for long periods of time can cause problems.

Whether you’re watching TV or working at your computer, it’s a good idea to frequently get up and take breaks from sitting still. If you are watching TV, try to move around every time there’s an ad break, or use an exercise bike whilst watching to ensure you are staying active.

What to read next...