Association between fat mass, lean mass, and bone loss: the Dubbo Osteoporosis Epidemiology Study

Lower body fat mass is a risk factor for bone loss at lumbar spine in postmenopausal women, but not in men. Body lean mass and fat mass were not associated with femoral neck bone loss in either gender.

Bone density and body mass are closely associated. Whole body lean mass (LM) and fat mass (FM) together account for approximately 95 % of body mass. Bone loss is associated with loss of body mass but which of the components of body mass (FM or LM) is related to bone loss is not well understood. Therefore, in this study, we sought to assess whether baseline FM or LM has predictive value for future relative rate of bone mineral density (BMD) changes (%/year).

The present population-based cohort study was part of the ongoing Dubbo Osteoporosis Epidemiology Study (DOES). BMD, FM, and LM were measured with dual energy X-ray absorptiometry (GE-LUNAR Corp, Madison, WI). BMD measurements were taken in approximately every 2 years between 2000 and 2010. We only included the participants with at least two BMD measurements at the femoral neck and lumbar spine. In total, 717 individuals (204 men and 513 women) aged 50 years or older were studied.

Rate of bone loss at femoral neck and lumbar spine was faster in women than in men (all P < 0.01). In bivariable regression analysis, each 5 kg greater FM in women was associated with 0.4 %/year (P = 0.003) lower bone loss at lumbar spine. This magnitude of association remained virtually unchanged after adjusting for LM and/or other covariates (P = 0.03). After adjusting for covariates, variation of FM accounted for ∼1.5 % total variation in lumbar spine bone loss. However, there was no significant association between FM and change in femoral neck BMD in either men or women.

Lower FM was an independent but modest risk factor for greater bone loss at the lumbar spine in women but not in men. If further studies confirm our findings, FM can help predict lumbar spine bone loss in women.