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How does TV watching increase health risk?

Wednesday, February 17, 2010 Posted by Travis Saunders

Yesterday morning I came across a very interesting study on Dr Yoni Freedhoff's blog Weighty Matters.  Yoni described a new study published in the American Journal of Public Health which suggests that the amount of commercial television (e.g. television with advertisements) that children watch before the age of 6 is associated with increased body weight 5 years down the road, even after adjustment for other important variables including physical activity, socio-economic status and mother's BMI.  In contrast, watching non-commercial television (DVD's or TV programs without commercials) showed no association with body weight.  The data was self-reported, but nonetheless these are pretty interesting findings, and suggest that television commercials are likely an important mechanism linking screen time with obesity risk.  

Now of course this makes a lot of sense - the more commercial television a child watches, the more junk food ads that they will be exposed to.  And the whole point of junk food advertisements are to get kids to eat more junk food.  For a reminder of just what these ads are like, below is a 1992 commercial for Coco Puffs (email subscribers can view the video by clicking on the title of the post).

So I agree completely with Yoni's conclusion that we need to keep food advertising away from children (In fact, TV watching in adolescence is associated with poor diet in early adulthood, so maybe we should ban food adverts altogether...).  This makes sense for a whole lot of reasons.  But, if we prevent children from being exposed to food advertising, will the relationship between television watching and health risk completely disappear?  Probably not.

Sedentary time (which includes TV time) is linked with all manner of health problems - from abdominal obesity to reduced insulin sensitivity, and even mortality.  And as we have discussed in the past, these relationships are usually found to be independent of physical activity.  In other words, no matter how much time you spend engaging in physical activity, the more time you spend sitting, the greater your health risk. 

One mechanism that is likely to link TV time (and overall sedentary time) with increased health risk is the relationship between TV viewing and junkfood ads that we discussed above.  Research also suggests that eating while watching TV may result in greater food intake than eating when not watching TV, which is likely another important mechanism linking TV time with health risk.  But these mechanisms focus on the relationship between screen time and increased body weight, and do little to explain the strong association of sedentary time with numerous metabolic risk factors independent of body weight.  For example, Sardinha and colleagues report that the more time that children spend being sedentary, the greater their risk of insulin resistance, even after control for both total and abdominal fat mass. So, how can sedentary time influence health risk independent of adiposity?

It turns out that engaging in sedentary behaviours like TV watching results in rapid and dramatic changes in skeletal muscle.  For example, in rat models, it has been shown that just 1 day of complete rest results in dramatic reductions in muscle triglyceride uptake, as well as reductions in HDL cholesterol (the good cholesterol).  And in healthy human subjects, just 5 days of bed rest has been shown to result in increased plasma triglycerides and LDL cholesterol, as well as increased insulin resistance - all very bad things.  And these weren't small changes - triglyceride levels increased by 35%, and insulin resistance by 50%!

These negative changes are likely related to reductions in the activity of lipoprotein lipase, an enzyme which allows muscle to uptake fat, thereby reducing the amount of fat circulating in the blood (it also strongly influences cholesterol levels - the details can be found here).  Animal research has shown that lipoprotein lipase activity is reduced dramatically after just six hours of sedentary behaviour - not unlike a work day for many individuals. Sedentary behaviour may also reduce glucose transporter protein content in the muscle, making it more difficult for glucose to be taken into the muscle, and resulting in higher blood sugar levels.  What is most interesting though, is that these mechanisms have little or nothing to do with the accumulation of body fat.  This means that both lean and obese individuals (and even those with otherwise active lifestyles), are at increased health risk when they spend excessive amounts of time sitting down.

What's the take-home message? 

Although it's impact on food intake is very important, TV watching (like all forms of sedentary behaviour) is also likely to result in rapid changes in skeletal muscle function, causing dramatic increases in metabolic risk, even for lean or otherwise physically active individuals.  The good news?  Animal research suggests that simply walking at a leisurely pace may be enough to rapidly return these metabolic risk factors to normal levels. 

So, let's work to prevent children from bring exposed to food advertisements, but let's also focus on reducing all forms of sedentary behaviour. 

Travis Saunders 

ResearchBlogging.orgZimmerman, F., & Bell, J. (2009). Associations of Television Content Type and Obesity in Children American Journal of Public Health, 100 (2), 334-340 DOI: 10.2105/AJPH.2008.155119

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7 Response to "How does TV watching increase health risk?"

  1. Anonymous Said,

    I admit, the TV is almost always on at my house. But it's pretty rare that all I do is watch it - I'm usually at least knitting, or working on the computer, or playing tug-of-war with the dog. But I 'watch' TV while I cook, fold the laundry, pick up and clean, and sew, and I have to wonder how many people are truly sedentary while watching TV and if/how the TV effects your health if you're not just laying there like a slug while you watch.

    Rather like the Wii (I still believe that, if you play it 'right', it gives you a good workout - no, no different from jogging in place or doing jumping jacks, but... if it's the *same* as those things, which are excersize, and I'm *more* likely to do it... how is that not an okay thing?) I think it all depends on how you use it.

    Posted on February 17, 2010 at 1:57 PM

  2. Travis Saunders Said,

    Thanks for the note!

    I agree that, like everything, TV's impact depends on how you use it. But like the Wii, I'm skeptical that many people actually use it in a way that is active. From my own experience, I know that I tend to move less when the TV is on simply because my eyes are drawn to it. For the vast majority of people, I would expect that having the TV on would result in them moving less than they would otherwise.

    What does everyone else think?


    Posted on February 17, 2010 at 5:42 PM

  3. Anonymous Said,

    By the same token, then, does sitting and reading increase your health risk? As much as watching TV? Is it the lack of movement, or are the adverts really that much of a factor? Though you'd have to consider the type of book - reading a mystery where the main character is a gourmet chef or the proprietor of a cookie shop would probably have a different effect than a book on corpses or autopsy techniques. At least you hope...

    Posted on February 18, 2010 at 5:31 AM

  4. justjuliebean Said,

    I don't think it's something inherent about tv, though it IS less active than reading. I think it's mostly that people like to snack while watching. Sedentary lifestyles, in my opinion, are extremely bad for health. I knew it was about a lot more than mood, but didn't know lots of details. I figure I can get away with eating some less than healthy things occasionally because of all the exercise I do.

    Posted on February 18, 2010 at 10:40 AM

  5. Sue Said,

    Do you guys remember what it was like to have TVs like the one in your photo, with dials and knobs? I do - you had to get up and cross the room every time you wanted to change the channel or the volume. People were thinner in those days. Maybe it's time to ditch the remote and put the buttons back on the set.

    Posted on February 18, 2010 at 3:54 PM

  6. Travis Saunders Said,

    You make an interesting point, Sue. There is some interesting cross sectional evidence that suggests that even just taking the odd break (e.g. standing for a few minutes) can reduce your risk of disease, compared to someone who spends the same total volume of time sitting, but without moving around from time to time.

    I have colleagues who suggest using the commercial break as a cue to stand and perform 2-3 minutes of movement - whether it be intense movement like running up the stairs or simply walking to the kitchen and back. I'd be curious to know if anyone has tried this technique at home!

    Posted on February 18, 2010 at 4:23 PM

  7. africangenesis Said,

    The junk food ad hypothesis seems weakly supported by the data. Perhaps commercial television was more interesting to the children so they were in the sedentary watching behavior a bit more than those watching commercial free television who did more active playing while in front of the television. The DVD watchers may be more likely to be watching something they've seen before, so even if the program was origially more interesting, the children may also be more selective about when they pay attention rather than more actively entertaining themselves. Some DVD programs like Seven Brides for Seven Brothers might actually get the children up an singing and dancing, despite the repitition or rather even because of it. So the actual content of the program needs to be controlled for. It would also be interesting to control for DVRs among the commercial TV watchers since they are less likely to watch commercials.

    Posted on September 2, 2010 at 7:23 AM


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We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.


The opinions expressed here belong only to Peter and Travis and do not reflect the views of any organization. Any medical discussion on this page is intended to be of a general nature only. This page is not designed to give specific medical advice. If you have a medical problem you should consult your own physician for advice specific to your own situation.

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