Watching too much TV can be fatal, a new study has found.
Hours of inactivity slumped in front of a television raises the risk of dying from a blood clot in the lungs, say scientists.
The 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 of TV watching per day increased the risk of fatal pulmonary embolism by 40%.
Participants who watched five or more hours of TV programmes daily were more than twice as likely to die than those watching less than 2.5 hours.
Spending 2.5 to 4.9 hours watching television raised the risk of embolism death by 70%. During the 19-year follow-up period, a total of 59 pulmonary embolism deaths were recorded.
Pulmonary embolism is a highly dangerous condition closely linked to inactivity and slowed blood flow. It usually begins as a clot in the leg or pelvis which breaks free and becomes lodged in a small blood vessel in the lungs.
More than a quarter of people who suffer an untreated pulmonary embolism die, and death can be sudden.
Lead researcher Professor Hiroyasu Iso, from Osaka University, said: "Pulmonary embolism occurs at a lower rate in Japan than it does in Western countries, but it may be on the rise.
"The Japanese people are increasingly adopting sedentary lifestyles, which we believe is putting them at increased risk."
Deaths from pulmonary embolism are thought to be under-reported and the actual risk may be greater than the findings suggest, say the authors writing in the American Heart Association journal Circulation.
The scientists took account of factors that 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.
Co-author Dr Toru Shirakawa, also from Osaka University, 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 Prof 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 pointed out.