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Tuesday, October 9, 2007

Exercise more critical than calcium for adolescent bones

The study of 80 women is part of the Penn State Young Women's Health Study, an ongoing
observational study begun in 1990 with the enrollment of 112 healthy female adolescents who are representative of Caucasian females attending public schools in Pennsylvania. The Penn State researchers followed the natural progression of cardiovascular, reproductive and bone health in these women.

For 10 years, researchers tracked a number of factors. Body composition and hip bone measurements were taken yearly with a dual X-ray absorptiometry (DXA) bone densitometer. Although bone mineral density has been widely used as the primary means of determining bone fracture risk, it is not a direct measurement of bone strength, which depends on both the material and structural properties of bone. So, the research team used recently-developed software to calculate specific measures of bone strength and geometric properties from the DXA data.

The team also collected calcium intake information by recording three-day diet records every six months for the first four years of the study and then yearly thereafter. Total average calcium intake in the group was between 618 mg/day and 1498 mg/day.
Oral contraceptive use was recorded, and physical activity was determined using a sports exercise questionnaire that listed 28 activities including school-based activities like soccer and marching band, outside of school activities like dance and aerobic classes, and individual activities like walking and running. A cumulative exercise score was calculated from the 10 years of data.

Study results showed that no significant relationship exists between average daily calcium intake and total bone gain from ages 12 to 22 or in young adult hip bone mineral density. A comparison of the oral contraceptive users and nonusers showed no difference in total body and hip bone mineral density suggesting oral contraceptives have no effected on bone density.
"Our statistical analysis of sport-exercise in adolescence showed that exercise is responsible for between 16 percent and 22 percent of the variation in hip bone mineral density and bending strength," Lloyd said. "Overall, data from the Penn State Young Women's Health Study indicates that daily calcium intake greater than 500 mg/day during adolescence does not result in clinically appreciable increased body bone accrual or increased adult bone mass."
Lloyd said additional, similar longitudinal studies of other ethnic and racial groups are needed to more fully evaluate the importance of the results for American women.

The study team included: Moira Petit, Ph.D., and Hung-Mo Lin, Sc.D., Department of Health Evaluation Science, Penn State College of Medicine, and Thomas J. Beck, Sc.D., Department of Radiology, Johns Hopkins University. The study was funded by the U.S. Department of Health and Human Services and the General Clinical Research Center at Penn State Milton S. Hershey Medical Center.

Contact: Valerie Gliemvgliem@psu.edu814-865-9481Penn State

Original Article Date: 09 Jun 2004 - 9:00 PDT

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