Every hour spent watching television increases the risk of dying from heart disease by almost a fifth.
And couch potatoes are also far more likely to die from other causes, including cancer.
tv-lovers who watch more than four hours a day are 80 per cent more likely to die for reasons linked to heart and artery disease, compared with those watching less than two hours a day.
Researchers in Australia monitored 8,800 adults for six years to see what impact watching TV had on their long-term health.
They found that each hour spent per day in front of the television increased the risk of death from all causes by 11 per cent.
It also raised the risk of dying from cancer by 9 per cent and the risk of heart disease-related death by 18 per cent.
The scientists warned that it was not only telly addicts whose lazy lifestyles put them in danger.
Any prolonged sedentary behaviour, such as sitting at an office desk or in front of a computer, posed similar risks, they said.
Interestingly, it also made no difference whether or not a person was overweight or obese.
?Even if someone has a healthy body weight, sitting for long periods of time still has an unhealthy influence on their blood sugar and blood fats,? said lead researcher Professor David Dunstan, from the Baker IDI Heart and Diabetes Institute in Victoria, Australia.
The average amount of TV people watch each day is three hours in both Australia and the UK, said the scientists.
In the US, where two-thirds of adults are overweight or obese, some people spent as much as eight hours watching television - the equivalent of a nine to five working day.
