Being a couch potato — even if it's only a part-time position subsidized with exercise — can seriously increase risk of heart disease and premature death, suggests a study released Monday.

Researchers in the United Kingdom compared the effects of spending different lengths of time in front of a screen — whether watching television, using the computer or playing video games — during non-work hours.

Their data showed that people who spend more than four hours each day on these activities are more than twice as likely to have a "major cardiac event" that can lead to hospitalization or death.

"People who spend excessive amounts of time in front of a screen, primarily watching TV, are more likely to die of any cause and suffer heart-related problems," said Emmanuel Stamatakis, from the University College London's department of epidemiology and public health. "Our analysis suggests that two or more hours of screen time each day may place someone at greater risk for a cardiac event."

This study represents the first time researchers have examined the association between screen time and cardiovascular health, the authors said.

There was an approximate 125 per cent increase in risk of heart-related health issues among test subjects who spent more than two hours per day being entertained in front of a screen, compared to those who spent less than two hours in watching the little glowing boxes, the study found.

The scope of this study did not focus on determining the precise causes of the increased risk, but researchers — who said the results were independent of traditional risk factors such as smoking, exercise and hypertension — said that metabolic factors and inflammation may partly explain the link.

The possibility that sick people were spending more time in front of their televisions and computers was ruled out, the authors said.

The researchers said their findings have prompted them to lobby for public health guidelines to address "recreational sitting," especially since more people are spending an increasing number of their hours sitting — whether during a commute, at work, or during their leisure time.

""It is all a matter of habit. Many of us have learned to go back home, turn the TV set on and sit down for several hours. It's convenient and easy to do," Stamatakis said. "And according to what we know so far, these health risks may not be mitigated by exercise."

The next step researchers hope to take is to unveil the short- and long-term effects of prolonged sitting, and to determine whether physical exercise can curb those effects, Stamatakis said.

The results of the study will be published in the Jan. 18 issue of the Journal of the American College of Cardiology.