Associations between body composition and bone loss in early postmenopausal women.

The early postmenopausal period is characterized by rapid bone loss, accompanied by a decline in lean mass and an increase in fat mass, highlighting the importance of understanding how these changes influence bone health. This study aimed to assess the cross-sectional and longitudinal associations between body composition and bone characteristics in early postmenopausal women using linear mixed models for repeated measures. A total of 223 Swedish women, aged 50-60 and within 1-4 yr postmenopause, were followed for 2 yr as part of the ELBOW II clinical trial. Body composition-body weight, appendicular lean mass (ALM), and fat mass-was assessed by DXA. Bone outcomes included areal BMD at the TH, FN, LS (DXA), as well as tibia bone microarchitecture and volumetric BMD (vBMD), measured by HR-pQCT. Higher baseline body weight, BMI, fat mass, and ALM were significantly associated with greater cortical area, cortical vBMD, and total vBMD. Baseline body weight, BMI, and fat mass, but not ALM, were positively associated with TH BMD. Longitudinally, increases in ALM were significantly associated with favorable changes in TH BMD, LS BMD, total vBMD, trabecular bone volume fraction, and cortical area. Changes in body weight and BMI were associated with multiple bone outcomes, while fat mass change was linked only with cortical area. In exploratory group comparisons, women with low baseline fat mass (28.14%) and greater ALM loss (∆% ALM: -2.87 kg) experienced 2.4-fold and 5.2-fold greater reductions in TH BMD and tibia total vBMD, respectively, compared to those with high fat mass and maintained ALM. These findings underscore the importance of maintaining or increasing lean mass and preserving overall body weight to mitigate bone loss and reduce skeletal fragility in early postmenopausal women.