"But doing so is bad for the heart and our health in general," said Stamatakis, who along with the other study authors is advocating public health guidelines to warn of the risks of being inactive during non-work hours.

Such warnings are urgent, "especially as a majority of working age adults spend long periods being inactive while commuting or being slouched over a desk or computer," said the study in the Journal of the American College of Cardiology.

Researchers studied data from 4,512 adults who took part in the Scottish Health Survey of households.

The information on screen time came from self-reported data about TV or DVD watching, leisure time computer use and playing video games.

When scientists compared people who reported spending less than two hours a day in front of screen-based entertainment to those who spent four or more hours per day, they found a 48 percent higher risk of death from any cause.

In those spending just two or more hours per day in front of screen after work, they also found a 125 percent higher risk of cardiovascular events such as heart attack.

"These associations were independent of traditional risk factors such as smoking, hypertension, BMI (body mass index), social class, as well as exercise," the study noted.

However researchers were able to make associations between the levels of inflammation and cholesterol in sedentary people.

"One fourth of the association between screen time and cardiovascular events was explained collectively by C-reactive protein (CRP), body mass index, and high-density lipoprotein cholesterol," said the study.

CRP, an indicator of low-grade inflammation, was about twice as high in people who spent more than four hours of free time daily in front of a screen compared to people who spent less than two hours a day.

Stamatakis said he intends to continue to study how prolonged sitting impacts human health and how lifestyle changes could be advocated to reduce the amount of time people spend inactive. (AFP)