The more a 3-year-old watches television, the more he or she consumes sugary drinks, and extra calories, Harvard researchers said today at the American Heart Association's 47th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.
"For every one-hour increase in TV viewing per day, we found higher intakes of sugar-sweetened beverages including juice (one extra serving per week) and total calories (46.3 more kcal/day)," said Sonia Miller, B.A., lead author of the study and a student at the Harvard Medical School.
Miller and her colleagues based their research on questionnaires from mothers of 1,203 children enrolled at birth in Project Viva, a study of childhood nutrition in Massachusetts funded by the National Institutes of Health. Just as more TV watching was associated with increased intakes of less healthful foods and nutrients, the researchers said it was also associated with decreased intakes of more healthful foods and nutrients, including fruits and vegetables, calcium and dietary fiber.
"Although 46 calories a day doesn't sound like much, it can make a difference in weight over time," said Matthew Gillman, M.D., S.M., senior author and associate professor of ambulatory care and prevention and director of the Obesity Prevention Program for Harvard Medical School and Harvard Pilgrim Health Care.
"Studies estimate that you can explain the amount of excess weight gain in the U.S. adolescent population over the past 10 years or so with the addition of only 150 calories a day. If this "energy gap" also applies to younger children, then each hour of daily TV or video watching could explain about 1/3 of that increase," Gillman said.
This study shows that poor dietary habits -- both more adverse practices and fewer healthy ones such as fruit and vegetable intake -- are associated with increased TV or video viewing, patterns associated with obesity and cardiovascular problems, he said.
Furthermore, these trends were found after researchers controlled for possible confounders such as maternal sociodemographic factors and parental body mass index (a measure of degree of overweight). Of the 1,203 children, 87 percent came from families with incomes greater than $40,000/year and 72 percent of their mothers had at least a college degree, researchers said.
The average amount of TV/video viewing for the group was 1.7 hours per day, so most children in this study were in line with the American Academy of Pediatrics recommendation of zero hours of screen time up until age 2 and no more than two hours per day after age 2.
"We don't really know from this observational study whether kids are substituting unhealthful foods for the more healthful ones. All we can say is that we see a pattern of less healthful foods and nutrients with increased TV use," Gillman said.
Children can get a lot of physical activity even if they watch a lot of TV or get little physical activity even if they watch little TV. So most people think the strong relationship between TV viewing and overweight is due to the eating side of the obesity equation rather than the exercise side, Gillman said. That equation is energy in (calories from food) minus energy out (calories burned from exercise). After taking into account what kids need to grow, if the energy in exceeds the energy out, excess weight gain results.
"TV seems to affect the 'energy in' side," Gillman said. "Whether it is due to kids snacking in front of the TV or the advertisements causing kids to eat more of the food that's advertised, we don't know.
"The most important thing to note is that the obesity epidemic in this country involves not just adults, not just adolescents, not just school-age children, but all the way down to infants. No age groups are spared. And once a child is obese, it is very hard to treat. So obesity prevention is the way to go."
The American Heart Association recommends children limit sedentary behaviors, with no more than 1 to 2 hours per day of video screen/television and no television sets in children's bedrooms and encourages 60 minutes of moderate-to-vigorous play or physical activity daily.
Other co-authors are Elsie M. Taveras, M.D., M.P.H. and Sheryl Rifas-Shiman, M.P.H.
Ms. Miller was supported by the Harvard Medical School PASTEUR, Division of Nutrition, and Office of Enrichment Programs.
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