The open-source journal PLoS Medicine posted a research article on the correlation between the time children spend watching television and their risk for developing components of the metabolic syndrome. The researchers also look to see if there was a correlation between the time kids spend watching television and their level of physical activity.
In a nutshell, the researchers found that TV watching correlated to obesity but not necessarily to the other components of the metabolic syndrome. There was no real correlation between time spent watching TV and the amount of time spent on physical activity.
Here is the editor’s summary of the study (my comments will follow):
Childhood obesity is a rapidly growing problem. Twenty-five years ago, overweight children were rare. Now, 155 million of the world’s children are overweight, and 30–45 million are obese. Both conditions are diagnosed by comparing a child’s body mass index (BMI; weight divided by height squared) with the average BMI for their age and sex. Being overweight during childhood is worrying because it is one of the so-called metabolic-risk factors that increase the chances of developing diabetes, heart problems, or strokes later in life. Other metabolic-risk factors are fatness around the belly, blood-fat disorders, high blood pressure, and problems with how the body uses insulin and blood sugar. Until recently, like obesity, these other metabolic-risk factors were seen only in adults, but now they are becoming increasingly common in children. In the US, 1 in 20 adolescents has metabolic syndrome—three or more of these risk factors. Environmental and behavioural changes have probably contributed to the increase in metabolic syndrome in children. As a group, they tend to be less physically active nowadays and they eat bigger portions of energy-dense foods more often. Increased TV viewing during childhood (and the use of other media such as computer games) has also been linked to increased obesity and to poorer health as an adult.
Why Was This Study Done?
One popular theory is that TV viewing may affect obesity and other metabolic-risk factors by displacing PA. Instead of playing in the yard after school, the theory suggests, children laze about in front of the TV. However, there is limited evidence to support this idea, and health professionals need to know whether TV viewing and PA are related, and how they affect metabolic-risk factors, in order to improve children’s health. In this study, the researchers examined the associations between TV viewing, PA, and metabolic-risk factors in European children.
What Did the Researchers Do and Find?
The researchers enrolled nearly 2,000 children in two age groups from three areas in Europe. They measured the children’s height and weight, estimated how fat they were by measuring skin fold thickness, measured their blood pressure, and examined the levels of glucose, insulin, and different fats in their blood. The children completed a computer questionnaire about the lengths of time for which they watched TV and how often they ate while doing so, and their PA was measured using a device called an accelerometer that each child wore for four days. When these data were analyzed statistically, the researchers found that TV viewing was slightly associated with clustered metabolic risk (the average of the individual metabolic-risk factors). This association was due to an association between TV viewing and obesity—the children who watched most TV tended to be the fattest children. However, TV viewing was not related to PA. The most active children were not necessarily those who watched least TV. Most importantly, PA was related to all individual risk factors except for obesity and with clustered metabolic risk. These associations were independent of obesity.
What Do These Findings Mean?
These results suggest that TV viewing does not damage children’s health by displacing PA as popularly believed. The finding that the association between TV viewing and clustered metabolic-risk factors is mediated by obesity suggests that targeting behaviours like eating while watching TV might be a good way to improve children’s health. Indeed, the researchers provide some evidence that eating while watching TV is associated with being overweight, but the results of this post hoc analysis—one that was not planned in advance—need to be confirmed. Another limitation of the study is the possibility that the children inaccurately reported their TV watching habits. Also, because measurements of metabolic-risk factors were made only once, it is impossible to say whether TV viewing or lack of PA actually causes an increase in metabolic-risk factors.
Nevertheless, these results strongly suggest that promoting PA is beneficial in relation to metabolic-risk factors, but less so in relation to obesity in childhood. TV viewing and PA should be treated as separate targets in programs designed to reverse the obesity and metabolic-syndrome epidemic in children.
A couple of things. First, this was a study done on European children. If you’ve ever spent time in Europe you will know that children are more active there than they are in the US. Kids walk and/ride their bikes all over the place. In Europe, so far at least, there is not the pervasive fear of child molestation that there is in this country, so parents are much less fearful of letting their children run and play in their neighborhoods and even take buses and subways to other areas. I wouldn’t particularly think that TV in Europe would displace as much physical activity as it does in the United States. In addition, as anyone knows who has watched TV in Europe, there isn’t anything remotely close to the variety of programming we have here, so there really aren’t stations (the Cartoon Network, for example) that play to kids 24/7. I would bet that if this study were done in the US, there would be a correlation between TV watching and lack of physical activity.
Second, there was a correlation between TV watching and obesity. When you consider this along with the finding that there is no correlation between TV watching and reduced levels of physical activity, you’ve got to figure that these overweight TV watching kids must still run and play as much as those who don’t watch as much TV. Therefore, diet has to come into play. So, it’s a logical jump to say that TV watching influences diet, which, in turn, influences weight gain (even in Europe). Which brings us back to the substance of a previous post showing the influence of TV watching on the family diet thanks to marketers of junk food.