Playful to the bone

But most parents probably don’t look at their young children and worry about the dangers of osteoporosis. It’s a disease that strikes in old age, but new research by a multi-disciplinary team at The University of Iowa shows that an ounce of prevention during childhood could be the key to avoiding or slowing progress of a disease with no cure.

The research team, led by Kathleen Janz, associate professor of health, leisure, and sport studies in the College of Liberal Arts and Sciences, found that vigorous physical activity promotes bone density and that even active five-year-olds aren’t getting enough of the right activity to develop strong bones.

As part of the Iowa Bone Development Study, the group assessed 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.

Emma Pradarelli, daughter of Steve Pradarelli, assistant director of University News Services, leaps (and builds bone density) during a gymnastics class. Photos by Tim Schoon.

“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, as 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 the window for bone development is limited. 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,” Janz said.

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.”

The Iowa 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 these projects. In addition to Janz, other members of the team are: 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.

With this new information, the hard work of keeping kids safe and healthy becomes a little more fun. Untangle the jump rope and hang a new net on the basketball hoop. A little bone strain now will go a long way toward a long, upright, fracture-free life.

Article by Mary Geraghty Kenyon