Trajectories of areal bone mineral density significantly differ by patterning of femoral neck area and bone mineral content across the menopausal transition

Clinical use of areal bone mineral density (aBMD) to identify fracture risk assumes that aBMD reflects bone mineral content (BMC). Yet, aBMD is calculated using a ratio of BMC and bone area, thus declines in aBMD may reflect a decline in BMC, an increase in bone area, or both. This study identifies groups of individuals defined based upon patterns of change in BMC and bone area across the menopausal transition (MT). The Michigan Bone Health and Metabolism Study is a longitudinal study of women; participants aged 24-50 were recruited in 1992 and followed near annually through 2010. At each visit, a DXA of the femoral neck was assessed. This analysis is based upon data from 97 women with an observed non-surgical final menstrual period (FMP); a dual-energy X-ray absorptiometry (DXA) scan 10 yr before FMP; and at least one post-FMP DXA. Group-based trajectory modeling identified distinct patterns of bone change across the MT. Three trajectory groups were identified for both bone area and BMC. For bone area, 27.8% of women showed initial steep increases in bone area followed by a continued increase around the FMP ("Highest Bone Area" group). For BMC, 26% of women experienced a substantial BMC decline after the FMP ("Fastest BMC Decline" group). Women in the both the "Highest Bone Area" and "Fastest BMC Decline" groups experienced the greatest aBMD decline (mean 12.8% decrease, SD 8.1%) despite higher baseline aBMD. Consideration of BMC and bone area changes across the lifecourse represents a novel approach to understanding overall bone health, and may elucidate an at-risk group not identified on aBMD alone. This information may be highly informative in identifying women at greatest risk for low aBMD and future risk for fracture.