Potential influences of oral contraceptive use and physical activity on bone health : a one-year prospective study in young women Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1n79h7256

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  • Osteoporosis is a skeletal disease affecting 44 million Americans. A primary strategy to prevent osteoporosis is to develop a high peak bone mass in youth. Oral Contraceptives (OCs) alter hormones in women and could affect bone mass development. The interaction between OCs and skeletal mineralization is poorly understood. PURPOSE: Our aims were to 1) compare bone mineral density (BMD) of young women who had a history of OC use with regularly menstruating controls, 2) compare changes in BMD in controls, women who initiate OC use, and those who have a history of use, and 3) to evaluate predictive capabilities of physical activity and years of oral contraceptives use on changes in BMD. METHODS: We recruited women, 18 to 25 years of age, with a history of OC use and controls. BMD at the hip, whole-body, and spine (AP, g/cm² and width-adjusted lateral, g/cm³) was measured by dual-energy x-ray absorptiometry. Physical activity (METs) was measured via questionnaire and grip strength was evaluated using an isometric dynamometer. RESULTS: Groups were similar in body mass index (BMI), fat mass, grip strength, calcium intake and physical activity but controls were slightly older than OC users. In analysis of covariance (ANCOVA), controlling for age and BMI, controls had significantly greater BMD than OC users at baseline at the AP and lateral spine, hip, and whole-body (p<0.05). By ANCOVA (covariates = age at baseline, change in weight), oral contraceptive users had greater bone loss at L₃ in the lateral view than controls whereas, controls had greater increases in L₃ volumetric BMD, BMD of the total hip, and whole body than OC users (p<0.05). Stepwise regression results did not reveal years of oral contraceptive use, grip strength, or METs to be a significant predictor of changes in BMD at any site. CONCLUSIONS: We conclude that, in the cross-sectional analysis, oral contraceptive use by young women may compromise bone health during a time when mineral is still accruing. In the prospective analysis, regularly menstruating controls had greater BMD accrual or less bone loss over a 12-month time period than women with a history of oral contraceptive use.
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