Tuesday, February 16, 2010

Are TV commercials solely responsible for screen time weight?

What a great study.

The authors analyzed the television viewing habits of 2,037 children between the ages of 0 and 12 back and the outcome they were interested in was BMI. Parents were given diaries where they tracked among other things the format of the television their children watched. Formats could be educational viewing on broadcast or cable (shows like Sesame Street), education viewing on DVD or video (same shows as on cable but without advertisements), children's entertainment viewing on DVD or video (such as Disney movies or advertisement free television cartoons), children's entertainment viewing on broadcast or cable, and lastly general audience viewing on broadcast or cable. Researchers also divided the children into groups below the age of 7 and above as those below 7 have been shown to be unable to differentiate truth from advertising.

They controlled for many variables. Physical activity, gender, age, ethnicity, sleep duration, eating in front of the television, mother's BMI, and mother's education.

The results were striking. For children younger than 7 each hour of commercial viewing was associated with a 0.11 increase in BMI scores after controlling for all of the aforementioned variables. For children older than 7, when controlled for all of the aforementioned variables and also the child's baseline BMI, again commercial viewing was once again significantly associated with increased risk of obesity.

The fact that the researchers controlled for so many variables and perhaps most importantly to challenging conventional dogma, physical activity, demonstrated to them that it's not what television is keeping kids away from (active play) that leads to obesity but rather that the viewing itself is causal for obesity and more specifically, the viewing of commercial advertisements.

Why might that be? The authors point out that children younger than 5 see an average of 400 television commercials each year (or 30 hours worth), during Saturday morning cartoons they see an average of 1 food ad every 5 minutes, and that 95% of foods advertised on television were of poor nutritional value. Equally frightening? They point out that the average first-grade child can identify over 200 brands.

So what does all this mean? It means it's probably not about how much they're watching, it's about what they're watching and while efforts to get kids off the couch to play certainly can play a role in reducing the burden of childhood obesity, it's not the playing that helps, it's getting them out of marketers' cross hairs.

Given that to date there has not been a single public health intervention that has led to long term reductions in screen-time, shouldn't we instead be focusing our efforts on enacting legislation to ban television based food marketing to children in general?

Zimmerman, 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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  1. As a cable customer paying around $100/month for services, I'd love to have the option to block advertising, similar to the way parental controls work where you can be as selective or liberal as you want (certain shows only, certain channels only, certain times only, etc). Surely the mass revenue from subscribers should have equal power to the revenues generated by advertisers?


  2. I strongly favor parents rather than polititians being in charge of television viewing.

    In the U.S., the First Amendment to our Consitition that protects the right of food sellers to advertise their wares.


  3. Great post Yoni. I agree completely about the importance of advertising, but there are some really interesting mechanisms that link sedentary behaviour with metabolic risk independent of obesity. So I'm not sure we should put all of our eggs into the advertising basket just yet. I talk about the other mechanisms in a (long-winded) post on our site that is scheduled to go up later today. Let me know what you think.

    I'll admit that I don't know of any public health interventions that have reduced screen time, but have there even been any public health interventions focused on screen time? I certainly can't think of any large ones. Personally, I think we really need to put more of a focus on reducing screen time (and sedentary behaviour in general), not less.

    Thanks for discussing this interesting paper!


  4. Hey Travis,

    Thanks for the note.

    I feel like a broken record but I'll say it again. I'm all for reducing screen time and increasing active play - just not in the name of treating or preventing childhood obesity.


  5. I think you've just basically summarized my post from today (with respect to sedentary time at least). For me personally, the links between exercise/sedentary time and metabolic risk independent of obesity are the ones that are most interesting.

    Congrats on the 1,000 post plateau! 5 or 6 more years and we might get there too!