July 16, 2012 -- The more television a child watches, even in the first years of life, the more likely he or she is to be thicker around the middle and less muscularly fit, according to a new study.
Previous studies have linked lots of television with childhood obesity and other child health detriments, but this study's authors say their report is the first to relate how time in front of the boob tube affects a specific measure of physical fitness, their explosive leg strength, an important asset for sports like soccer, basketball and football.
Caroline Fitzpatrick, the study's lead author, said the measure isn't just important for children who want to be athletes.
"Explosive leg strength is an important measure of a child's overall physical fitness, their general muscular fitness," she said.
Fitzpatrick and her colleagues at the University of Montreal studied more than 1,300 children from across Quebec. When the children reached age 2 and age 4, the researchers asked parents how many hours per day their children spent watching television. On average, the 2-year-olds watched almost 9 hours of TV each week; by the time they reached age 4, average weekly TV viewing rose to nearly 15 hours.
A few years later, when the children were in second and fourth grades in school, the researchers measured their waist size and also how they performed on the standing long jump, hoping to measure each child's explosive leg strength.
The researchers were able to translate hours in front of the TV to centimeters of physical size and performance. They calculated that each hour of television watched during the week as a 2-year-old corresponded to a 0.361-centimeter decrease in a child's performance on the standing long jump. If a child watched an hour more of television as a 4-year-old than they did when they were 2, that corresponded to 0.285 centimeters shaved off of their jump. That extra hour of TV time also corresponded to a 0.047-centimeter increase in waist size.
The study was published Sunday in the International Journal of Behavioral Nutrition and Physical Activity.
Fractions of centimeters don't seem like they are that important, Fitzpatrick acknowledged.
"But on a small child, a centimeter becomes important," she said.
And considering that most children watch more than one hour of TV every day, those fractions of centimeters really start to add up. Fitzpatrick and her colleagues noted that 15 percent of the children in their study watched more than 18 hours of TV each week, corresponding to a 0.76-centimeter increase in their waist size by age 10.
Measuring waist size isn't only about physical appearance. Abdominal fat is also a predictor of heart health, back pain and other physical ailments, in both children and adults.
The study's findings are one more indictment of the impact television viewing may have on children's health.
Rahil Briggs, director of the Healthy Steps program at Montefiore Medical Center in Bronx, N.Y., said the study doesn't prove that TV sets make children unhealthy, and the act of watching television itself is not necessarily evil.
"But it [TV viewing] comes at the expense of other age-appropriate and healthy things children should be doing," she said. "There are only so many hours in the day, and if children are watching TV, that's cutting into the hours of the day they could be doing something active."
Even though not all children will turn out to be football stars or champion sprinters, their athletic abilities are important not only for physical health, but predicting how physically active they will be as adults.
Phil Tomporowski, a professor of kinesiology at the University of Georgia, said factors such as a child's leg strength, motor control and balance can impact how well they perform at games and sports that they play with their peers. How they perform there can impact how confident they are in their physical abilities, and some studies have found that kind of confidence is important even in adulthood.
"Confidence plays a key role in whether children as adolescents or adults choose activities that are active and healthy promoting or more sedentary," Tomporowski said.
Though the study doesn't mention other sources of excessive screen time for kids, such as video and computer games, it does recommend that parents stick to the American Academy of Pediatrics' recommendations on TV viewing for kids: Children older than 2 should watch less than two hours of TV per day, and children younger than 2 shouldn't watch TV at all. Fitzpatrick suggested that TV time could be replaced by going outside, playing with blocks or other activities that are "developmentally enriching."
Briggs said the findings of this study suggest that parents who let their children watch TV may want to consider an additional tradeoff.
"If your child watches two hours of TV, maybe they should offset that with two hours of physical activity," she said.