Timing and Duration of Hormone Replacement Therapy and Bone Mineral Density in Postmenopausal Women

Abstract

0754 Although hormone replacement therapy (HRT) is widely prescribed to postmenopausal women to prevent or slow bone loss, few studies have examined bone responses to the timing of HRT use (i.e., when HRT was initiated relative to menopause) in postmenopausal women. In addition, the relationship between bone mineral density (BMD) of the vertebral bodies measured in the lateral projection and HRT use is poorly understood. PURPOSE: To evaluate differences in BMD of the third lumbar vertebrae (L3) assessed the anterior-posterior (AP) and lateral projections in postmenopausal women according to timing and duration of HRT use. METHODS: We recruited 109 women (ages 46–90) from ongoing studies in the Bone Research Laboratory in which spine BMD was measured by DXA, and physical activity, dietary intake, and medication use were collected via questionnaire. We conducted a between group analysis of L3 BMD in women with four distinct HRT profiles: 1) no history of HRT use (NoHRT, n = 39); 2) HRT use continually since menopause (Cont, n = 43); 3) discontinuous HRT use initiated 5–10 years after menopause (Disc, n = 10); 4) HRT initiated within the previous 5 years and maintained (Recent, n = 17). In addition, a stepwise regression was performed to determine the relative contribution of years of HRT use on L3 BMD of the spine in comparison to age, calcium intake, and physical activity. RESULTS: An ANCOVA, controlling for age, indicated that there was no significant difference in L3 BMD in the AP or lateral views according to timing of HRT use. A stepwise regression analyses including years of HRT use, age, calcium intake, and physical activity level revealed that age and years of HRT use were the only significant predictors of L3 BMD in the lateral view [r2 = 0.07, (P <.01); r2 = 0.07, (P <.01) respectively] whereas age was the only significant predictor of L3 BMD in the AP view (r2 = .09, P <.01). Calcium intake and physical activity were not significant predictors of L3 BMD in any view. CONCLUSION: In this cross-sectional analysis of a small sample of postmenopausal women, BMD of the AP and lateral spine were similar regardless of timing of hormone replacement therapy. Also, since duration of HRT use and age were both predictors of lateral spine BMD while only age predicted AP spine BMD, lateral assessment of spine BMD may be superior to AP when evaluating HRT and vertebral bone mass.