Associations of Age at Menopause With Postmenopausal Bone Mineral Density and Fracture Risk in Women

CONTEXT: Menopause before age 45 is a risk factor for fractures, but menopause occurs at age ≥45 in ~90% of women. OBJECTIVE: To determine, in women with menopause at age ≥45, whether (1) years since the final menstrual period (FMP) is more strongly associated with postmenopausal bone mineral density (BMD) than chronological age and (2) lower age at FMP is related to more fractures. DESIGN AND SETTING: The Study of Women's Health Across the Nation, a longitudinal cohort study of the menopause transition (MT). PARTICIPANTS: A diverse cohort of ambulatory women (pre- or early perimenopausal at baseline, with 15 near-annual follow-up assessments). MAIN OUTCOME MEASURES: Postmenopausal lumbar spine (LS) or femoral neck (FN) BMD (n = 1038) and time to fracture (n = 1554). RESULTS: Adjusted for age, body mass index (BMI), cigarette use, alcohol intake, baseline LS or FN BMD, baseline MT stage, and study site using multivariable linear regression, each additional year after the FMP was associated with 0.006 g/cm2 (P < 0.0001) and 0.004 g/cm2 (P < 0.0001) lower postmenopausal LS and FN BMD, respectively. Age was not related to FN BMD independent of years since FMP. In Cox proportional hazards regression, accounting for race/ethnicity, BMI, cigarette use, alcohol intake, prior fracture, diabetes status, exposure to bone-modifying medications/supplements, and study site, the hazard for incident fracture was 5% greater for each 1-year decrement in age at FMP (P = 0.02). CONCLUSIONS: Years since the FMP is more strongly associated with postmenopausal BMD than chronological age, and earlier menopause is associated with more fractures.