Every hour spent watching TV each day increases the risk of dying from heart disease, say scientists.
Couch potatoes were warned that their lifestyle also increased the risk of death from other causes including cancer.
Individuals who spent hours watching television greatly heightened the chances of dying early from heart attacks and strokes, they found.
Compared with those watching less than two hours of TV, people who sat in front of the box for more than four hours a day were 80pc more likely to die for reasons linked to heart and artery disease.
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 11pc.
It also raised the risk of dying from cancer by 9pc and the risk of heart disease-related death by 18pc.
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.
"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.