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Stanford Report, May 5, 1999

For kids, reducing TV viewing may be a key to preventing obesity


A Stanford study suggests that, for grade-school children, watching less television may be a key to limiting weight gain. Children who were involved in a one-year curriculum to reduce their TV viewing gained significantly less body fat than a control group of their peers.

The study of 192 third- and fourth-graders from two San Jose elementary schools is important not only for showing a connection between TV watching and body weight, but it is also some of the first evidence that a behavioral program delivered in schools can motivate children to ration their TV viewing, said the study's author, Thomas Robinson, MD, assistant professor of pediatrics and medicine. Robinson thinks this program is a promising population-wide approach to help prevent childhood obesity, which he says has reached epidemic proportions.

"One of the things that makes this study unique was that it focused specifically on reducing TV, videotape and video game viewing without promoting any other activities as substitutes," Robinson said. "As a result, we were able to isolate the effects of these media alone."

Robinson presented his results May 4 at the Pediatric Academic Societies annual meeting in San Francisco.

American children have become fixated on television and now spend, on average, more than four hours a day watching TV and videos or playing video games, according to nationwide surveys. Only sleep consumes a larger share of the average child's day. And more and more children and adults are now overweight. Rates of childhood obesity have more than doubled over the past two decades, Robinson said.

To physicians and public health experts, this epidemic of obesity is alarming. Overweight children tend to become overweight adults, who are more likely to develop life-threatening health problems like diabetes and heart disease. The amount of time kids spend immobile in front of the TV has frequently been blamed as a cause of obesity. That proposal sounds eminently logical, Robinson said, but epidemiological studies seeking a link between number of hours watched and weight have found only a weak relationship, he noted.

All of these studies have looked for correlations between the TV viewing and body weight without manipulating the amount of TV watched. Robinson approached the problem differently by trying to alter TV habits and then subsequently measuring the effect on body weight. As a result, this was the first experimental test of the TV-obesity hypothesis in normal school children.

Local education officials picked two schools with similar ethnic composition, socioeconomic standing and scholastic achievement. At one of the schools, the third- and fourth-graders received an 18-lesson program, presented by their classroom teachers as part of the normal school curriculum, that was designed to reduce TV and videotape watching and video game playing. Both schools agreed to participate before learning which school would receive the curriculum, and the students at each school were found to have similar TV viewing habits and body fatness at the beginning of the school year, Robinson said.

TV-reduction lessons began by encouraging children to keep track of how much time they spent watching TV and videos and playing video games. In the next step, the children were encouraged to go 10 days without TV ­ something that two-thirds of them accomplished. Then the lessons turned to setting TV-watching limits of 7 hours per week and becoming more selective viewers.

At the beginning and the end of the school year, pupils at both schools filled out surveys about their media use, diet and exercise habits. Their body fat was measured, and they took a physical fitness test. Parents also completed interviews about their own and their children's habits.

To account for normal growth and maturation, Robinson compared the change in different body measurements between the two schools over the course of the school year. Children attending the school that had received the TV-reduction lessons did reduce their television watching by about one-third to one-fourth, compared with their peers. Over the course of the study, they also showed a significantly smaller increase in waist size, waist-to-hip ratio and body mass index, a measure of weight adjusted for height. For example, the average pupil at the TV-reduction school gained nearly 2 pounds less than the average student at the control school.

However, the two schools didn't differ in consumption of high-fat foods, amount of moderate-to-vigorous exercise, or physical fitness. So if the kids weren't exercising more or eating a healthier diet, Robinson needed to try to account for the weight difference. Robinson said one possibility was that the kids were performing more low-level activities ­ more energetic than simply sitting still but less energetic than walking. Freed from the TV, the children may simply have been moving around more, though this kind of activity is extremely difficult to measure, Robinson said.

However, the difference may also stem from changes in the number of meals the kids ate in front of the TV. The children at the TV-reduction school significantly decreased the number of meals they ate while watching TV. Even a small change in caloric intake could account for the difference in weight gain, Robinson noted. For example, the calorie equivalent of one additional regular soft drink per day translates into a yearly weight gain of about 15 pounds, he said.

"These are the largest effects on body composition we have seen from any obesity prevention program we have studied to date," said Robinson. "But our enthusiasm has to be tempered because the results come from only a two-school study."

Robinson's study was funded by a grant from the American Heart Association, California Affiliate. He subsequently has received a grant from the National Heart, Lung and Blood Institute to replicate the study with 900 students from 12 elementary schools. That research has just begun and will also involve Stanford researchers Joel D. Killen, PhD, associate professor of medicine; Helena C. Kraemer, PhD, professor of psychiatry and behavioral sciences; William Haskell, PhD, professor of medicine; Leslie Pruitt, PhD, research associate in medicine; and Donna Matheson, PhD, a post-doctoral scholar in pediatrics. SR