Jan 16 For children, time spent actually
inactive - such as lying on the couch - appears to have less of
an impact on how much body fat they have than a lack of exercise
does, according to a U.S. study.
Researchers, whose study appeared in the Journal of
Pediatrics, found that the more minutes children spent
exercising at the pace of a fast walk each day, the lower their
percentage of body fat. But the time they spent lying around
made no difference.
"Our study supports the current physical activity guideline,
that's what I want people to know," lead author Soyang Kwon, a
pediatric researcher at Northwestern University in Chicago, told
The U.S. Department of Health and Human Services recommends
that children and teens exercise at least at the intensity of a
fast walk, about 5.6 kilometres per hour (3.5 miles per hour),
for 60 minutes every day.
Last year, a study in adults found a different result:
regular exercise doesn't protect against the dangers of sitting
for many hours at desk jobs. This is likely because children are
more active than adults overall.
"In adults, where the activity levels are generally less,
the time spent sedentary may have more of an effect," said
Russell Pate, who studies physical activity in children at the
University of South Carolina in Columbia.
Kwon and her coauthors from the University of Iowa used data
from a study in that state that followed children of various
ages from 2000 to 2009.
A group of 277 boys and 277 girls were measured at eight,
11, 13 and 15 years old for body composition and fat content
using a precise X-ray technique originally developed to assess
The same children wore an accelerometer, which measures body
movement, for several days in a row sometime in the same year.
Even among children who exercised the least, the amount of
time sitting didn't make much of a difference.
For the 13-year-olds, those who sat less than, more than or
equal to the average six and a half hours per day all had about
the same body fat mass.
But boys who spend the least amount of time in moderate to
vigorous activity had about 5 kilograms (11 pounds) more body
fat on average than those who exercised the most. For
13-year-old girls, the low level exercisers had about 3.2 kg (7
lbs) more body fat than the exercisers.
Results were similar in every age group, but the researchers
did not record if each child was overweight or not.
In a previous study, the same team of researchers found that
even light intensity activity, like walking, every day, was
linked to lower levels of fat in teens, but not young children.
"Parents should encourage their children to be physically
active, the more the better," said Ulf Ekelund, who studies
obesity risk factors in children at the Norwegian School of
Sport Science in Oslo. "That might sound simple, but the
execution isn't so simple sometimes."
(Reporting from New York by Kathryn Doyle at Reuters Health;
editing by Elaine Lies)