To determine whether long-term exposure to exogenous estrogen in oral contraceptives influences trabecular bone mass in premenopausal women, we studied 25 closely matched, healthy, premenopausal women, who were recruited from an active obstetrics and gynecology practice. Eleven women had never used oral contraceptives, and 14 women had used oral contraceptives for a minimum of 67 months. All oral contraceptive users had used preparations that provided a minimum of 50 micrograms mestranol per day. Trabecular bone density was determined by quantitative single-energy computerized tomography of the L1-3 lumbar vertebral bodies. Trabecular bone density was similar for both the control group and the oral contraceptive users, 160.6 +/- 6.9 versus 161.2 +/- 7.4 mg/ml, respectively. The power to detect a 15% difference in bone density between these two samples was 0.87. We concluded that long-term, premenopausal oral contraceptive use has no effect on vertebral bone density.
PIP: Although oral contraceptives (OCs) cause a depression of circulating estrogen to near postmenopausal levels, longterm OC use does not appear to lead to a reduction in trabecular bone density. In this study, trabecular bone density was determined by quantitative single-energy computerized tomography of the L1-3 lumbar vertebral bodies and compared in 14 longterm OC users (mean use of 120 months) and 11 never users. The controls and OC users were closely matched to eliminate as many potentially confounding variables as possible. Trabecular bone density was basically similar for both groups--160.6 + 6.9 for controls versus 161.2 + 7.4 mg/ml for cases. The power to detect a 15% difference in bone density between these 2 groups was 0.87. It is concluded that premenopausal OC use has neither a beneficial effect nor an appreciable negative effect on bone density after longterm use. If a threshold estrogen level is required for normal premenopausal bone remodeling, such a threshold is not reached by the depression of plasma estrogen levels during OC use. It should be noted that this study measured only the trabecular portion of vertebral bone, which is known to respond more rapidly than cortical bone to metabolic stimuli.