July 16, 2012, TIME
By Alexandra Sifferlin
The more TV kids watch in early life, the thicker they get around the waistline and the weaker their muscle strength, a new study finds.
It’s no secret that watching TV is linked with some unhealthy outcomes in kids — previous studies have found that children who watch more television are more likely to eat junk food, have trouble sleeping and become obese — but the new study, published in BioMed Central’s open access journal International Journal of Behavioral Nutrition and Physical Activity, establishes a link between screen time and specific measures of physical fitness.
“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,” said senior author Dr. Linda Pagani, a researcher at the Sainte-Justine University Hospital Research Center, in a statement.
The researchers looked at 1,314 kids who were participating in the Quebec Longitudinal Study of Child Development. The parents of the kids reported the number of hours they spent watching TV each week: at the start of the study, when the the kids were 2.5 years old, they were watching about 8.8 hours of TV per week on average. Over the next two years, TV time increased by six hours to 14.8 hours weekly on average. By age 4.5, about 15 percent of the kids in the study were watching more than 18 hours of television each week.
The more time kids spent in front of the TV, the larger their waistlines, the researchers found: each additional hour of weekly TV logged between age 2.5 and 4.5 was linked with an increase of waist size of slightly less than half a millimeter by the time the kids were in grade school. So, a child who watches 18 hours of television at 4.5 years old will have gained an extra 7.6 millimeters (0.3 in.) around his middle by age 10.
Fractions of inches may not sound like much to worry about, but even small increases are significant on child-size bodies, and over time, these little changes add up. Waist size in particular is known to be associated with overall obesity and also with measures of visceral fat, the type of fat that hides around the organs deep in the gut and is especially risky to health.
“Our study is the first to look specifically at waist measurements,” says lead author Dr. Caroline Fitzpatrick. “The weight around the waist is particularly dangerous in terms of cardiovascular and metabolic health.”
The researchers measured both waist size and another indicator of physical fitness: explosive leg strength. When the kids were 8.5 years old, the researched gauged their performance on the standing long jump in order to measure their leg-muscle power, a key contributor to sports ability. Kids who watched more TV as preschoolers were more likely to end up in the bottom 5 percent of long-jump performance: each hour spent watching TV per week at age 2.5 corresponded to about a third of a centimeter loss in jumping distance.
That’s important for all kids, not just those who want to play soccer or basketball. Muscle power is associated with other markers of health and fitness: according to Fitzpatrick, if you have good muscle fitness, you’ll also have better cardiovascular fitness and be less susceptible to injuries. The authors write:
This suggests that for some children, excessive television exposure was associated
with the experience of a substantial level of impairment. This finding is of concern
given that explosive leg strength is a robust indicator of individual general muscular
strength. Eventually, reduced muscular strength that persists into adulthood can
predict a number of negative health outcomes.
“Kids who watch more TV are known to be less involved in physical activity and less inclined to play sports, but we found there is actually a potential risk in decreasing their athletic performance with too much television,” says Fitzpatrick. “This can influence their health as adolescents and adults.”
Fitzpatrick says the findings are concerning since young kids are still undergoing through muscular and skeletal development. “It’s a move it or lose it problem,” she says.
The American Academy of Pediatrics recommends that children over age 2 watch no more than two hours of television per day; younger kids should watch no TV at all. Each hour a kid spends planted in front of the tube is an hour he or she isn’t exercising, playing or doing any other constructive activity like reading. “When it’s cold outside, you want a kid to throw on their snow gear and go play instead of preferring to stay inside to watch hockey on TV,” says Fitzpatrick.