Each hour of TV watched by a two- to four-year- old contributes to his or her waist circumference by the end of grade 4 and his or her ability to perform in sports, according to a world-first study undertaken by researchers at the University of Montreal and its affiliated Saint-Justine Mother and Child University Hospital.

The findings were published July 16 by lead author Dr. Caroline Fitzpatrick and senior author Dr. Linda Pagani in BioMed Central's open access journal the International Journal of Behavioral Nutrition and Physical Activity. "We already knew that there is an association between preschool television exposure and the body fat of fourth grade children, but this is the first study to describe more precisely what that association represents," Pagani explained. "Parents were asked about their child's TV habits. Trained examiners took waist measurements and administered the standing long jump test to measure child muscular fitness. We found, for example that each weekly hour of TV at 29 months of age corresponds to a decrease of about a third of a centimeter in the distance a child is able to jump."

In addition to providing an important indicator of health, in the form of muscular fitness, the standing long jump test also reveals an individual's athletic ability, as sports such as football, skating, and basketball require the "explosive leg strength" measured by the test. "The pursuit of sports by children depends in part on their perceived athletic competence," Fitzpatrick said. "Behavioural dispositions can become entrenched during childhood as it is a critical period for the development of habits and preferred activities. Accordingly, the ability to perform well during childhood may promote participation in sporting activities in adulthood."

Along with their parents, 1314 children from the Quebec Longitudinal Study of Child Development database participated in this study. When the children were 2.5 to 4.5 years of age, their parents reported how many hours of television during the week and weekend they watched. The average was 8.8 hours per week at the onset of the study, a figure that increased on average by 6 hours over the next two years to reach 14,8 hours per week by the age of 4.5 year. Thus, 15% of the children participating in the study were already watching over 18 hours per week according to their parent's reports at that time.

In terms of waist size, the researchers found that, at 4,5 years of age, the children's waist size increased by slightly less than half a millimetre for every extra weekly hour of TV the child was watching on top of what they had been watching when he or she was 2.5. To put it another way, a child who watches 18 hours of television at 4.5 years of age will by the age of 10 have an extra 7.6 milllimetres of waist because of his or her habits.

The researchers stress that while further research should be undertaken to establish that television watching is directly causing the health issues they observed, the study that was just published should encourage authorities to develop policies that target the environmental factors associated with childhood obesity. "The bottom line is that watching too much television -- beyond the recommended amounts -- is not good," Dr. Pagani said.

"Across the occidental world, there have been dramatic increases in unhealthy weight for both children and adults in recent decades. Our standard of living has also changed in favor of more easily prepared, calorie-dense foods and sedentary practices. Watching more television not only displaces other forms of educational and active leisurely pursuits but also places them at risk of learning inaccurate information about proper eating. These findings support clinical suspicions that more screen time in general contributes to the rise in excess weight in our population, thus providing essential clues for effective approaches to its eradication." Children over the age of two should not watch more than two hours of television per day, according to the recommendations of the American Academy of Pediatrics.