While the debate over television's effects on kids focuses on what they watch, a new study of about 4,000 children underscores the importance of how much, showing that the more time they spend in front of the tube, the fatter they tend to be.
Moreover, the study firmly documents for the first time that black and Mexican American youths watch more TV than do whites, putting them at greater risk of obesity. Spending more than four hours a day in front of the TV were 43% of African American children, 30% of Mexican Americans, and 20% of non-Hispanic whites.
One reason for the ethnic and racial differences in viewing trends, researchers speculate, is that parents in urban neighborhoods may discourage their children from playing outside because of crime. Thus the fear of crime appears to contribute to the "epidemic of obesity," researchers say.
Though it may seem obvious that watching TV and shirking exercise is behind the childhood obesity epidemic, researchers have had surprising difficulty nailing down those factors, with some previous studies showing no correlation between TV viewing habits and kids' fatness.
The new study's results, made public today in the Journal of the American Medical Assn., "are consistent, make sense, and indicate a serious problem in the United States," said Steven Gortmaker, a sociologist at the Harvard School of Public Health who has studied TV viewing and obesity.
In the most comprehensive study of its kind, the researchers analyzed data from lifestyle interviews with 4,063 children between 1988 and 1994. Consistent with previous surveys, the study found high rates of TV viewing overall: 67% watched at least two hours a day, and 26% racked up four or more hours.
The central finding was that kids who watched a lot of TV were measurably fatter than those who watched relatively little. For instance, children who watched at least four hours daily had about 20% more body fat than those who watched less than two hours.
Body fat was estimated from height and weight as well as by using calipers that measure the thickness of skin folds on the abdomen and back.
The number of children who are obese, meaning 30% above their ideal weight, grew by 7% from the early 1980s to the early 1990s, according to federal survey data. That trend is troubling, public health experts say, because childhood obesity is often a harbinger of serious weight problems in adulthood, which contribute to heart disease, diabetes and other chronic diseases.
