Bingeing on TV box-sets could be fatal, research suggests.
Hours of inactivity slumped in front of a television sharply raises the risk of dying from a blood clot in the lungs, say scientists. A Japanese team studied the TV viewing habits of more than 86,000 people aged 40 to 79 between 1988 and 1990.
They found that every additional two hours viewing per day increased the risk of fatal pulmonary embolism by 40 per cent. Participants who watched five or more hours of programmes daily were more than twice as likely to die over the following 19 years than those who watched less than two and a half hours.
Researchers said those who planned lengthy television sessions should take the same precautions as those embarking on long-haul flights.
The scientists from Osaka University Graduate School of Medicine recommended a five minute walk every hour.
They said recent trends - such as "binge-watching" box sets via online streaming, and reliance on laptops and tablets - could put increased numbers at risk.
However, the overall risk of such deaths appeared low. Just 59 deaths from the fatal clots were recorded from among 86,000 cases tracked, though scientists said cases were likely to be under-reported, as the condition can easily be missed.
Pulmonary embolism is a highly dangerous condition closely linked to inactivity.
It usually begins as a clot in the leg or pelvis, but can become particularly dangerous if it breaks free and travels to the lung, becoming lodged in a small blood vessel, where it is particularly dangerous.
More than a quarter of people who suffer an untreated pulmonary embolism die.
Dr Toru Shirakawa, one of the researchers, warned against lengthy TV sessions that might involve back-to-back episodes of a favourite series.
"Nowadays, with online video streaming, the term 'binge-watching' to describe viewing multiple episodes of television programmes in one sitting has become popular," he said. "This popularity may reflect a rapidly growing habit."
It was possible to watch a lot of TV while taking simple precautions to avoid blood clots similar to those recommended for air travellers on long-haul flights, said the researchers.
"After an hour or so, stand up, stretch, walk around, or while you're watching TV, tense and relax your leg muscles for five minutes," said lead researcher Prof Hiroyasu Iso. He added that drinking water and losing weight may also help.
The study recorded viewing habits before computers, tablets and smartphones became popular sources of information and entertainment, said the scientists.
More research is needed to assess the effect of these new technologies on pulmonary embolism risk, they said.
Symptoms of the clots include chest pain and shortness of breath, so it can easily be mistaken for other conditions.
The study, reported in the American Heart Association journal Circulation, examined a range of factors which might have influenced their results, including levels of obesity, diabetes, smoking, and high blood pressure.
After the number of hours spent watching TV, obesity appeared to have the strongest link to pulmonary embolism.
Separate research published in the same journal found that women who did at least two and half hours of moderate exercise a week had a 25 per cent lower risk of heart disease.
The study of women aged 27 to 44 by the Indiana University School of Public Health found that frequency of exercise did not matter, as long as total weekly time was at least 150 minutes. Brisk walking was enough to make the difference.