PP25 Timing of menopause but not hysterectomy is associated with bone health in early old age: a british birth cohort study

Abstract

Background While many comparisons of the bone health of pre- and post-menopausal women, and studies of the effect of hormone therapy (HT) use on bone, suggest that oestrogen status is a key determinant of the rate of bone loss in post-menopausal women, studies have shown only a limited effect of timing of menopause on bone health. The MRC National Survey of Health and Development (NSHD), a British cohort born in 1946, has the advantage of a large sample of the same age, pQCT as well as DXA-derived bone measurements, a full HT history, and follow-up into early old age. Methods Up to 866 women from the NSHD who repeatedly provided information about the menopausal transition from age 43 and had a bone scan at the 60–64 year clinic examination were included in analyses. DXA derived measurements were areal bone mineral density (aBMD) for lumbar spine and total hip. The pQCT scans at the distal 4% site provided measures of trabecular and total volumetric BMD (vBMD) and distal cross-sectional area (CSA), and at the 50% site provided CSA of the diaphysis and the medullary cavity (medullary CSA) and cortical vBMD; polar strength strain index (SSI) (mm 3 ), an estimate of bone strength, was extracted. Regression models with outcomes transformed using natural logarithms were fitted so that the coefficients give the percentage difference for each bone parameter between women with natural or surgical menopause, or for a ten year difference in timing of natural menopause or hysterectomy. Models were adjusted for current height and weight, indicators of HT use, and other behavioural and socioeconomic factors. Results Women who had a later natural menopause had higher spine aBMD (8.9% difference, confidence intervals (CI)5.2%,12.6%), hip aBMD (6.4%, CI 0.3%,9.5%), trabecular vBMD, (9.4%, CI 0.3%,16.3%), and total vBMD (6.8%, CI 0.1%,12.2%) than women with an age of menopause ten years earlier, even after adjusting for potential confounders. In contrast, timing of hysterectomy had no clear association with bone health. Women who had a hysterectomy had greater hip and spine aBMD, total and trabecular vBMD, and polar SSI than women who had a natural menopause: however, these differences were mainly accounted for by body size and HT use. Conclusion These findings indicate that the association between the timing of natural menopause and bone mineral density persists into early old age.