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By ALICE PARK Alice Park Wed Aug 5, 4:00 am ET
It's no secret that sedentary behavior contributes to obesity and chronically
poor health. But not all sedentary behaviors are created equal, according to a
new study that examines the link between blood pressure in children and their
choice of inactive pastimes, including watching TV, using the computer and
reading.
Researchers in the U.S. and Spain collaborated on the study of 111 children
ages 3 to 8 and found that of all the forms of inactivity they examined,
television-viewing was the worst. It was linked to significantly higher blood
pressure in children - the more TV kids watched, the higher their blood
pressure - and the effect held true regardless of whether a child was heavy or
at a healthy weight. What's more, other sedentary behaviors, like using a
computer, were not associated with similar blood-pressure hikes, according to
the study, which was published in the Archives of Pediatric and Adolescent
Medicine. (See the 100 best TV shows of all time.)
"These results show that sedentary behavior, and more specifically
television-viewing, is related to blood pressure independent of body fat or
obesity level," says Dr. Joey Eisenmann, a kinesiologist at Michigan State
University and one of the study's co-authors.
To determine levels of inactivity over one week, the children in the study wore
accelerometers, which resemble pedometers but instead of tracking distance,
they record the body's acceleration in a vertical plane - sitting results in a
score of zero, and walking and running produce progressively higher scores. The
researchers considered anything under a score of 50 per day as sedentary. They
coupled this data with reports from the children's parents about how much time
the kids spent in inactive pursuits, including watching television, sitting at
a computer, playing video games, reading or doing other projects that don't
require much movement.
The children were sedentary for five hours each day, and 1.5 of those hours
were spent in front of a TV, computer or video game, on average. When the
researchers further broke down screen time by activity, TV-viewing had the
strongest correlation with higher blood pressure. Kids watching from 90 to 330
minutes of television each day had systolic and diastolic blood-pressure
readings (the two numbers that indicate pressure caused by blood pumping from
the top and bottom chambers of the heart, respectively) that were five to seven
points higher than those of children watching less than half an hour of
television a day. (Read about how sex on TV increases the risk of teen
pregnancy.)
"These results show that TV-viewing really is the worst of all possible
sedentary activities," says Dr. David Ludwig, director of the Optimal Weight
for Life Program at Children's Hospital Boston, who was not part of the study.
The American Academy of Pediatrics recommends that children under 2 should not
watch any television and that older children limit their viewing to one to two
hours per day.
So what is it about watching TV that's worse than playing video games or
surfing the Internet? Certainly, playing games and using computers involve some
movement, like fidgeting or changing body positions, but is that enough to
explain the difference? The study's authors propose several other possible
explanations. For instance, beyond the complete inactivity involved with
TV-viewing - which alone raises the risk of high blood pressure - children may
be compounding their sloth by eating junk food. "A full bag of chips or a plate
of hot dogs can disappear a lot more quickly while watching TV than they might
at any other occasion," says Ludwig. And the types of foods that children are
likely to be eating in front of the tube, like salty snacks, can push up blood
pressure readings.
See the top 10 TV ads of 2008.
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In addition, say the authors, if kids watch TV too close to bedtime, their
minds may remain stimulated just enough to keep them awake and miss out on
precious hours of sleep. Cutting short a good night's slumber, past research
suggests, can lead to weight gain and hypertension, since the body's metabolism
doesn't have enough opportunity to recharge and renew itself overnight.
To those reasons, Ludwig adds a few others. Previous studies have found that
watching television lulls people, especially young children, into a low-energy
state that is akin to sleeping - that's about as sedentary as a person can get.
"Some studies suggest that the metabolic rate can fall even below that of
sleeping," he says. "They suggest that children are getting into some deep
hypnotic state at times." (See the top 10 TV series of 2008.)
Worse yet is the content of television programming, which Ludwig suggests may
have long-lasting repercussions. "There is the possibility that the greatest
long-term impact of TV viewing is on children's eating habits through food
commercials," he says. Some experts estimate that youngsters are bombarded with
10,000 food commercials each year during children's programming, and most of
them aren't promoting salads or fruit. All this marketing, says Ludwig, changes
children's taste preferences and causes them to crave - and beg for - unhealthy
foods. "Children are seeing these commercials at an age when they are just
establishing eating habits that can become ingrained and last a lifetime," he
says.
Eisenmann stresses that while the new study found an association between
TV-viewing and higher blood-pressure readings, it did not measure whether
children developed hypertension. However, in previous studies involving the
same group of children, whom he and the other scientists have been studying for
four years, about 20% of the children had developed prehypertension or
hypertension - often because of weight gain.
Although the study did not follow the children over time, the findings still
suggest that TV-viewing has a strong influence on the health of young children.
Environmental and lifestyle factors, like diet and inactivity, account for
about 70% of a person's blood pressure (genes determine the rest), and high
blood pressure at a young age may increase kids' risk of developing heart
disease in adulthood. "There is no fundamental biological need for TV-viewing
in childhood," says Ludwig. "So these findings certainly warrant follow-up."