There's no shortage of research showing links between watching too much television and early death. But what is it about vegging in front of the box that is so bad for you?
Sometimes it seems as though everything that's enjoyable in life is bad for your health, and television is no exception.
A number of studies have found links between watching television and premature death, and the more you watch, the more it reduces your lifespan.
It's been estimated that once you're over 25, every hour of television you watch reduces your life expectancy by close to 22 minutes.
But it isn't terrible scripts, bad acting or excruciating reality TV programs that are shaving years off our lives; it's what we do, or rather don't do, when we're zoning out in front of the box.
For most us, watching television means sprawling on the couch for extended periods. And extended inactivity is known to increase your risk of heart disease, type 2 diabetes, some types of cancers and premature death.
Physical activity researcher from Baker IDI Heart and Diabetes Institute Dr Brigid Lynch says one reason sedentary behaviour has such a significant impact on your health is because you expend less energy when you're sitting or lying down than when you're on your feet, just standing or walking around.
"Over hours of the day, days of the week and weeks of the year that is all going to add up and contribute to weight gain and a shift in how much energy you are expending," she says.
But there's also evidence that when our muscles are idle, it slows down the release of enzymes that help to control the level of fats and sugars in your blood.
"When you are sitting down, particularly if you're sitting on the couch and really reclining, you're not actually engaging those [skeletal] muscle groups [in your core, legs and spine]. They are all relaxed.
"And we know that skeletal muscle plays a really important role in metabolic function. So even though you aren't running or using weights, those skeletal muscles play a really important role in glucose regulation and helping to regulate the lipid levels in our blood."
Something else?
But a recent study from Spain suggests that there might be something else happening when we watch TV. The researchers found people who watched more than three hours of television a day had double the risk of premature death when compared to those who watched less than one hour per day. But when they looked at other sedentary behaviours – driving a car and using a computer – they didn't find the same links with early death. They say more research is needed to help figure out whether there are links between computer use or driving and death rate.
But why might TV be linked with premature death when other types of sedentary or inactive behaviour aren't?
Lynch says it might just be that TV watching is more easily measured, giving clearer and therefore more reliable results.
"When we're doing studies and we're asking people to actually recall how long they are spending doing these types of sedentary behaviours – people are pretty good at remembering the amount of time they watch TV for."
But it's also possible some of the behaviours that go hand in hand with watching telly might be contributing to its unhealthy effects, Lynch says.
You don't get off the couch: When you watch TV it's possible you may not stand up for several hours, and research shows even standing up for a minute or two every 20 minutes helps your body regulate important substances such as glucose, fuel for all the body's cells, and the hormone insulin, which enables cells to access and use glucose. "It's fairly unlikely you are going to be sitting at your desk looking at email for several hours without popping up to go and do something else."
TV's affect on food choices: "We know people tend to snack when they are watching TV in the evening, and usually their snack of choice is not particularly healthy. So it's a bit hard to disentangle." There's also the possibility that when you're watching TV, you are being exposed to advertising of unhealthy food choices. If this ends up influencing what you buy and eat, it adds to the poor health effects of TV watching.
TV may be linked with social isolation: "We know there are a lot of health benefits to having that social interaction and maybe missing out on that, and spending a lot of time in front of the TV is taking that social interaction away from people and that's also contributing to their poor health outcomes." It's also the case that TV watching may be a result of social isolation, with people turning to the box because they have no social interactions to distract them.
While you don't need to give up TV, the Spanish researchers (and other experts) say you should limit the amount of time you spend watching TV to less than one to two hours a day. And when you are watching try to:
- Get up and move around every now and again, rather than remain entirely motionless. Consider standing for short periods of watching or do a standing chore like ironing for some of the time.
- Put your remote control away so you are forced to get up to use manual controls.
- Don't make your favourite TV show an excuse to eat junk food.
As for those excruciating reality TV shows? Health experts warn you watch them at your own risk...
