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Children’s exercise program increases bone mass, not fracture risk

NEW YORK (Reuters Health) – A moderately intense four-year exercise program in children aged seven to nine increased their bone mass and size without affecting fracture risk, in the Malmö (Sweden) Pediatric Osteoporosis Prevention Study

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“It is possible to improve bone health in the population without an increased risk of fracture by increasing the physical education in school,” Dr. Bjarne Löfgren from Lund University told Reuters Health by email. “Whether the exercise-induced skeletal benefits received during childhood remain into adulthood and provide a feasible strategy to prevent osteoporosis remains to be investigated.”

Dr. Löfgren and colleagues reported Monday in Pediatrics that the exercise group (808 participants) incurred 51 fractures during the study, a rate of 19.1 events/1000 person-years, compared with 97 fractures in the 1,587 participants in the control group, a rate of 17.1 events/1000 person-years. The difference was not statistically significant.

The groups did not differ in the trauma energy that caused the fracture, and there were no stress fractures in either group.

Girls and boys in the intervention group had longer duration and higher intensity of physical activity than did girls and boys in the control group.

Mean annual bone mineral content increases during the study period were 7.0% higher in the lumbar spine and 4.1% higher in femoral neck for girls and 3.3% higher in the lumbar spine and 0.6% higher in the femoral neck for boys in the exercise group than same-gender subjects in the control group.

After children were divided into tertiles of physical activity, there was a dose-response effect between duration of physical activity and annual gain in bone mineral content and bone width.

“The largest difference with regards to gain in bone mineral content was observed between tertile 1 and 2 for both boys and girls,” Dr. Löfgren said. “In other words, it seems that it’s the least active children who benefit most from the extra physical education.”

“What’s known from previous studies regarding exercise-induced gain in bone mass is that it’s probably better to have several shorter periods of physical activity than few longer periods, which is primarily shown in animal models,” Dr. Löfgren continued. “Most likely, it’s best to be a little active every day. Current international guidelines recommend that children participate in at least 60 cumulative minutes of moderate to vigorous physical activity per day, through a variety of activities. In addition to this, it is recommended that children engage in muscle-strengthening and bone-strengthening activity at least three days per week.”

“We are planning a follow-up of these children each year regarding bone parameters and fractures for nine years, that is, through primary school, until the children are 15-16 years old,” Dr. Löfgren added.

SOURCE: http://bit.ly/Kj0GMf

Pediatrics 2012;129:e1468-e1476.