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

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(2) = 0.009; P =.014). Adjusted mean vertebral bone mineral density was 3.3% greater for premenopausal women (partial r(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.