CONTACT: MARY GERAGHTY KENYON
300 Plaza Centre One
Iowa City IA 52242
(319) 384-0011; fax (319) 384-0024
Release: Oct. 16, 2001
UI study shows kids need more activity for healthy bones
IOWA CITY, Iowa -- Anyone who has ever watched five-year-olds zipping around
a playground will be shocked to learn that even this most active segment of
the population isn't getting enough of the right activity to develop strong
That is the result of a study by a multi-disciplinary team at the University
of Iowa, led by Kathleen Janz, associate professor of health, leisure, and
sport studies in the College of Liberal Arts and Sciences. The group studied
470 children between ages four and six and monitored the amount and intensity
of their activity with a device worn at the hip that recorded minute-by-minute
movement information for four days.
When the study began, researchers measured the children's bone density and
bone mineral content in order to compare it with activity measures. The children
who were most active, especially those doing vigorous activity, were much
more likely to have more bone mineral content and denser bones than children
who did little vigorous activity. Janz and her team theorize that many children
are not involved in the right kinds of activity to promote the development
of stronger bones.
"Kids need to be jumping, tumbling, hopping, or otherwise engaged in
activities that strain the bone with impact," Janz said. "That's
what causes the bone to grow denser, just as working muscles by lifting heavy
loads in strength training enhances muscle development."
The amount of activity is not as important as the type, she said. The research
suggests that kids can increase their bone density by up to 3 percent with
just 15 additional minutes of the right types of activity per day.
Janz said it is crucial for children to start early in developing strong,
dense bones because there is a limited window for bone development. In most
cases, bone growth peaks during late adolescence or early adulthood, so by
the time people reach their early 30s they have all the bone they ever will
have and actually begin losing it gradually. Once bone loss begins, those
with lower bone density will experience negative effects like osteoporosis
much sooner than those with greater bone density. "It's like backing
people up from a starting point and expecting them to run the same race,"
Even more disturbing, Janz said, is that the girls in the study were less
active than the boys, which leaves them lagging behind boys in developing
healthy bones from a very young age. Since women already do not develop the
bone strength that men do because of smaller mass and hormonal differences,
Janz said it is even more critical for young girls to become involved in activities
that promote bone development.
"We need to get girls involved in sport and give them the opportunity
to do other types of vigorous activity that they enjoy, like dance and jumping
rope," she said. "It's not a stretch to speculate that we're creating
the next generation of osteoporotic women due to inactive lifestyle."
This research is part of the Iowa Bone Development Study, a longitudinal
study of Iowa children. The Bone Development Study grew out of the Iowa Fluoride
Study, which began 10 years ago and continues to measure the effects of fluoride
exposure and ingestion in 800 Iowa children. Steven M. Levy, professor of
preventive and community dentistry, is the primary investigator for the fluoride
study. The team includes: Trudy Burns, professor of biostatistics, Teresa
Marshall, visiting assistant professor of dentistry, James Torner, professor
and head of epidemiology, John Warren, assistant professor of preventive and
community dentistry and Marcia Willing, associate professor of pediatrics.