It is enough to put anyone off binge-watching their latest favourite box set.
Spending too long in front of the television can dramatically raise the risk of developing deep vein thrombosis.
More commonly associated with long-haul flights and hospital patients, deep vein thrombosis can also occur from sitting too long, cutting off vital blood flow to the legs.
A US study found people who watch television ‘very often’ are 71 per cent more likely to get a potentially fatal blood clot in their leg.
Spending too long in front of the television can dramatically raise the risk of developing deep vein thrombosis
This type of clot can lead to either deep vein thrombosis (DVT) or a pulmonary embolism – blood clots in the lungs.
Watching television is the most common sedentary activity worldwide, and people who spend too much time in front of the box are more likely to be obese and unfit.
But the study of more than 15,000 people aged 45 to 64 concludes that even people who exercise are at risk.
The study’s lead author, Kasuhiko Kubota, from the University of Minnesota, said: ‘These results suggest that even individuals who regularly engage in physical activity should not ignore the potential harms of prolonged sedentary behaviors such as TV viewing.
‘Avoiding frequent TV viewing, increasing physical activity and controlling body weight might be beneficial to prevent VTE [venous thromboembolism].’
A venous thromboembolism is either deep vein thrombosis or a pulmonary embolism.
This latest study is the first to focus on a Western population, who are known to be more prone to blood clotting conditions than people of Asian descent
The American participants were asked how often they watched television, from ‘very often’ to ‘never’.
The results show television addicts who answered ‘very often’ were 1.7 times more likely to suffer a venous thromboembolism than those who watched television seldom or never.
Those at greater risk of DVT include people over the age of 40 and people inactive for a long time in cramped conditions, such as after an operation or a long-haul journey on an aeroplane.
The condition affects 60,000 people a year in Britain and starts with pain, swelling and a heavy ache in the leg.
The US study, published in the Journal of Thrombosis and Thrombolysis, found obesity helped to explain the results in the 15,158 people given questionnaires.
But those watching the most were still at risk, regardless of their body mass.
There were 691 cases of DVT or pulmonary embolism among the study participants, which can lead to breathlessness, chest pain and collapse, requiring urgent medical attention.
Prolonged sitting disrupts the normal circulation of blood through the legs and feet, which slows blood flow and can lead a blood clot to form.
Deep vein thrombosis can lead to a pulmonary embolism when a clot dislodges and travels through the body to the lungs.
Findings from a 2016 study in Japan also highlighted the increased risk of suffering a VTE relative to the hours spent in front of the TV.
This latest study is the first to focus on a Western population, who are known to be more prone to blood clotting conditions than people of Asian descent.