MONDAY, Feb. 5, 2007 (HealthDay News) -- If your child isn't getting enough exercise, don't blame the "idiot box." New research suggests that the amount of time teens spend watching TV bears no relationship to their levels of physical activity.
The finding, which was published in the February issue of Pediatrics, runs counter to a commonly held couch-potato theory --embraced by many obesity-prevention programs -- that the more time children spend in front of a TV show or video game, the less time they'll play sports or exercise.
"Changes in television viewing do not necessarily predict changes in physical activity -- increases or decreases-- so we cannot just assume that if we can get kids to reduce their television viewing it will automatically result in increases in their physical activity," said study lead author Dr. Elsie M. Taveras. She's an assistant professor of pediatrics in the department of ambulatory care and prevention at Harvard Medical School.
Taveras and her colleagues examined the TV and exercise habits of almost 6,400 girls and 4,500 boys across the United States, who were between the ages of 10 and 15 when the four-year study began in 1997.
All the children were the sons and daughters of nurses who'd participated in an earlier study, and the vast majority was non-Hispanic whites.
The children completed four written questionnaires over the study period, in which they reported the number of hours they spent watching TV, as well as the amount of time they spent exercising outside of any school-required physical education classes.
TV viewing broadly included all video watching and video-game playing. In terms of exercise, moderate activities such as baseball, biking, dancing, skateboarding, walking, gymnastics, and volleyball were included, as were what the study authors deemed to be more strenuous activities, such as basketball, hockey, skating, swimming, soccer, tennis, jogging, football, and karate.
The authors found that for each additional hour a week that a child spent watching TV, their involvement in either moderate or vigorous exercise increased by just .03 hours a week. The researchers concluded that changes in television viewing habits year to year did not appear to be substantially related to changes in exercise habits.
This lack of an association held true for gender and age, with no apparent difference between boys or girls aged 10 to 12 and those aged 13 to 15.
The researchers suggested that public health programs designed to address adolescent obesity should view television watching and exercise as two independent activities with separate motivations.
But, Dr. Jess Shatkin, a child and adolescent psychiatrist, and director of education and training at New York University's Child Study Center, said any conclusions about a connection between TV watching and exercise is complicated by socio-economic factors.
"From a public health background, a lot of it comes down to what you can afford," he said. "This study doesn't directly address this, but it may be that while TV-watching is not by itself connected with exercise habits, the fact that a child doesn't live in a safe area may mean he stays inside more, doesn't exercise, and watches TV more so parents can keep tabs.
"And," Shatkin added, "for a variety of reasons, physical activity has become less of a priority in our public schools. So, if a child doesn't happen to live near a nice park, and the parents can't afford $300 for a T-ball class, then the kid is probably going to get less exercise whether or not he's watching TV."
Taveras acknowledged that point, noting that the children in the study came from families with higher-than-average economic backgrounds, in which at least one parent -- the mother -- was educated and employed as a health-care professional.
"So he [Shatkin] is absolutely right," she said. "Our findings are certainly valid for the group we looked at, but they may not be generalizable. They may not translate to someone who lives in the inner city, where there may not be the money to replace TV-viewing with gymnastics."
Taveras said her future research plans include examining the link between TV and exercise habits among lower-income families, as well as younger preteen children, to see if the findings hold true on a broader scale.
In a related study, researchers found that teens who spend a lot of time watching TV are more likely to have higher blood pressure, regardless of whether they are overweight.
"This is the first research to show a direct and independent connection between TV watching and higher blood pressure among adolescents," said study leader Dr. Nicolas Stettler, a pediatric nutrition specialist at The Children's Hospital of Philadelphia.
The study of 4,500 American teens found that sedentary activities and higher body mass index (a ratio of weight to height) were associated with higher systolic blood pressure. The findings are published in the February issue of the Journal of Adolescent Health.
For more information on exercise and health, visit the National Institutes of Health.