Too much TV, video and computer can make teens fatter

Even teens from the consistently low group exceeded two hours per day of screen time on average, yet organizations such as the American Academy of Pediatrics and the Canadian Paediatric Society recommend limiting screen use to two hours per day. Increasers and consistently high screen users had the greatest increases in percent body fat, while decreasers had the lowest gains in percent body fat

While the majority of adolescents in the study maintained a typical ''flat'' pattern of 25 to 30 hours of screen time per week, close to 30 percent of adolescents had screen time patterns that increased, decreased or remained high over time. The scientists found that these atypical' patterns had the greatest impact on weight gain.

"There is some concern that adolescents' television, video and computer use is filling much of their discretionary time" says lead author Tracie A. Barnett, a professor at the Université de Montréal's Department of Social and Preventive Medicine and a scientist at the Sainte-Justine Hospital Research Center. "Our findings show that youth are at greater risk of increased body fat if screen use increases through high school; one possible reason is that teens who increase their screen time are simultaneously reducing involvement in and opportunities for more active pursuits." Similarly, teens that had initially high levels of screen use but dropped their screen use over time ended up with the most favourable body fat profiles.

Dr. Barnett and her team evaluated 744 participants, as of grade 7, from 10 Montreal high schools. Teens reported screen time and their level of physical activity four times per year or a total of 20 times during the five-year study. The research team also measured height, weight and body fat of participants several times over the course of the investigation.

"The high levels of screen time observed in our study underscore the need for public health strategies to reduce overall screen time among youth. Encouraging less screen time, and some form of monitoring to prevent excessive increases in screen time through high school, would be beneficial to teenagers. Since most already have firmly established viewing habits at the start of high school, these strategies also need to target kids before they even begin high school," says Dr. Barnett.

The study was funded by the Canadian Cancer Society, the Fonds de la Recherche en Santé du Québec and the Canadian Institutes of Health Research.