An average of six hours a day in front of the box could shorten life expectancy by almost five years - about the same as other well-known risk factors such as smoking.
A study team used previously published data on TV viewing time and death from analyses of the Australian Diabetes, Obesity and Lifestyle Study (AusDiab), as well as Australian national population and mortality figures for 2008, to construct a lifetime risk framework.
And doing the math, they calculate that every single hour of TV watched after the age of 25 shortened life expectancy by 22 minutes.
Based on these figures, and expected deaths from all causes, the authors work out that someone who spends a lifetime average of six hours a day watching TV can expect to live just under five fewer years than someone who doesn't watch it at all.
What's surprising is how this figure compares with the effects of other lifestyle factors. For example, watching half an hour's TV has the same effect on life expectancy as smoking one cigarette.
Indeed, being a lifelong smoker actually shortens the life less than watching six hours' television a day, with the smokers kicking the bucket four years early compared to the couch potatoes' five.
"Substantial loss of life may be associated with prolonged TV viewing," the authors write in the British Journal of Sports Medicine. "While we used Australian data, the effects in other industrialised and developing countries are likely to be comparable, given the typically large amounts of time spent watching TV and similarities in disease patterns."
They conclude: "If these [figures] are confirmed and shown to reflect a causal association, TV viewing is a public health problem comparable in size to established behavioural risk factors."
Just tell me this: should I now be tearing my kids away from Spongebob Squarepants, and handing them a pack of Marlboros instead?