Many studies have found links between screen time and obesity. But the key may not be related to just having the TV on. What if what matters is how much a kid actually pays attention?
A recent study attempted to answer this question by getting beyond simply the link between screen time and weight.
The researchers measured how much teens were paying attention to different types of media during a full week. Then the researchers compared these results to the teens' weights.
The results showed that only more time spent paying attention to TV was linked to teenagers' weight. No link was found for computers, video games or background TV.
The study, led by David S. Bickham, PhD, of the Center on Media and Child Health at Children's Hospital Boston, investigated whether teens' weights varied according to what kind of media they used.
The researchers recruited 91 young teens, aged 13 to 15, to participate in the study and measured their body mass index (BMI). BMI is the ratio of a person's height to weight and is used to determine how healthy a person's weight is.
Then, over a one week period, the participants reported how they used their time with different types of media during weekdays and on Saturday. They wrote down how much time they used television, computers and video games.
At the same time, however, the participants also carried small, portable computers that paged the teens four to seven times each day. At that exact moment, the teens were asked on the computer screen to answer what activity they were paying the most attention to.
The teens also recorded what other activity they were paying the second most attention to and what additional activity they were paying the third most attention to.
In other words, if a teen was listening to an MP3 player while doing homework on a laptop and having the TV on in the background, they might be paying the most attention to the computer, the second most to the MP3 player and the third most to the TV.
The point of the study was to understand whether the link between weight and screen time found in past studies was related to the screens or more to how much kids were paying attention to certain media.
An analysis of the results showed no connection between the amount of time teens spent with computer and video games and their BMI. This result did not change depending on how much time the teens actually were paying more or less attention to video games or the computer.
With television, however, the findings were different. Just using the TV – having it on – was not linked with the participants' BMI. But specifically paying attention to TV did appear linked to BMI.
Basically, the top quarter of teens that paid the most attention to TV had an average 2.4 more BMI points than the bottom quarter of teens that paid attention to the TV least often.
A BMI of 18.5 to 24.9 indicates a healthy weight, and a BMI of 25 to 29.9 indicates being overweight. Individuals with a BMI of 30 or more are considered obese.
"These findings support the notion that attention to TV is a key element of the increased obesity risk associated with TV viewing," the researchers wrote. They noted that the reasons might relate to TV advertising for food or because teens eat more food while actually paying attention to the TV. However, more research is needed to understand these possible reasons better.
"It's important to be clear that we didn't test these specifically," Dr. Bickham told dailyRx regarding what the mechanisms might be linking TV watching and BMI. This study provides a basis for future work that looks for those mechanisms "...so we can make targeted recommendations and interventions," such as doing less unconscious eating during TV watching, Dr. Bickham said.
The element of food advertising is important to consider as well, said Deborah Gordon, MD, a dailyRx expert who specializes in nutrition.
"Although we all know that a correlation proves nothing and should only be taken as an opening for actual research, the study does call to mind other similar studies, such as one from UCLA earlier this year, that correlated merely living in neighborhoods with fast food billboards and increased obesity," Dr. Gordon said.
The study was published April 7 in the journal Pediatrics. The research was funded by the National Institute for Child Health and Human Development. The authors declared no conflicts of interest.