Oral contraceptives and bone mineral density: A population-based study

Byline: Julie A. Pasco, Mark A. Kotowicz, Margaret J. Henry, Soheila Panahi, Ego Seeman, Geoffrey C. Nicholson Keywords: Oral contraceptives; bone mineral density; epidemiology Abstract: Objective: We sought to test the hypothesis that exposure to oral contraceptives protects the skeleton. Study Design: Multiple regression techniques were used to analyze data for a random sample of 710 Australian women (age range, 20-69 years). Bone mineral density was measured at the lumbar spine, proximal femur, whole body, and distal forearm. Oral contraceptive exposure was assessed by a questionnaire. Results: Women exposed to oral contraceptives had a 3.3% greater mean bone mineral density adjusted for body mass index and age at the lumbar spine (partial r.sup.2 = 0.009; P = .014). Adjusted mean vertebral bone mineral density was 3.3% greater for premenopausal women (partial r.sup.2 = 0.008; P < .05), but the effect did not reach significance among postmenopausal women. Higher bone mineral density was associated with increased duration of exposure, with a mean increase of 3.2% associated with the first 5 years and a further 0.2% with [greater than or equal to]5 years of exposure. No association was detected at other sites. Conclusion: Exposure to oral contraceptives may be associated with higher lumbar spine bone mineral density. (Am J Obstet Gynecol 2000;182:265-9.) Author Affiliation: Geelong, Victoria, Australia From the Departments of Medicine, St Vincent's and The Geelong.sup.a and Austin & Repatriation.sup.b Hospitals, the University of Melbourne Article History: Received 15 March 1999; Revised 12 July 1999; Accepted 23 September 1999 Article Note: (footnote) [star] Supported by the Victorian Health Promotion Foundation and the Geelong Region Medical Research Foundation., [star][star] Reprint requests: Julie A. Pasco, PhD, The University of Melbourne, Department of Medicine, The Geelong Hospital, PO Box 281, Geelong 3220, Australia.