(PhysOrg.com) -- The association between television viewing and childhood obesity is directly related to children's exposure to commercials that advertise unhealthy foods, according to a new UCLA School of Public Health study published in the American Journal of Public Health.
The study, conducted by Frederick J. Zimmerman and Janice F. Bell, is the first to break down the types of television children watch to better determine whether different kinds of content may exert different effects on obesity.
The researchers gathered data from primary caregivers of 3,563 children, ranging from infants to 12-year-olds, in 1997. Through time-use diaries, study respondents reported their children's activities, including television viewing, throughout the course of an entire weekday and an entire weekend day.
Caregivers were also asked to report the format — television programs, DVDs or videos — and the names of the programs watched. This data was used to classify television viewing into either educational or entertainment programming and to determine whether or not it contained advertising or product placement. A follow-up was conducted in 2002.
The analysis controlled for the amount of physical activity and the children's gender, age, race/ethnicity, mother's body mass index (BMI), education and sleep time.
Among all children, commercial viewing was significantly associated with higher BMI, although the effect was stronger for children younger than 7 than for those older than 7, the study found.
"The persistence of these results, even when the child's baseline weight status was controlled, suggests that the association between commercial television viewing and obesity does not arise solely or even primarily because heavier children prefer commercial television," said Zimmerman, professor and chair of health services at the School of Public Health and the lead author of the study.
Non-commercial viewing, including watching DVDs or educational television programming, had no significant association with obesity.
According to the authors, the findings strongly suggest that steering children away from commercial television may be effective in reducing childhood obesity, given that food is the most commonly advertised product on children's television and the fact that almost 90 percent of children begin watching television regularly before the age of 2.
By the time they are 5 years old, children have seen an average of more than 4,000 television commercials for food annually. During Saturday morning cartoons, children see an average of one food ad every five minutes. The vast majority of these ads — up to 95 percent — are for foods with poor nutritional value, the researchers say.
"Commercial television pushes children to eat a large quantity of those foods they should consume least: sugary cereals, snacks, fast food and soda pop," Zimmerman said.
The authors conclude that the availability of high-quality, enjoyable and educational programs for all ages on DVD should make it relatively easy for health educators and care providers to nudge children's viewing toward content that does not contain unhealthy messages about food and eating.
"Just as there are far better and more nutritious foods than those advertised on television, there are also far better and more interesting shows on television than those supported by advertising," Zimmerman said. "Educational television has come a long way since today's parents were children, and there are now many fantastic shows on commercial-free television and, of course, wonderful content available on DVD."
Explore further: Suddenly health insurance is not for sale