Disentangling the body weight-bone mineral density association among breast cancer survivors: an examination of the independent roles of lean mass and fat mass

Background: Bone mineral density (BMD) and lean mass (LM) may both decrease in breast cancer survivors, thereby increasing risk of falls and fractures. Research is needed to determine whether lean mass (LM) and fat mass (FM) independently relate to BMD in this patient group. Methods: The Health, Eating, Activity, and Lifestyle Study participants included 599 women, ages 29-87 years, diagnosed from 1995-1999 with stage 0-IIIA breast cancer, who underwent dual-energy X-ray absorptiometry scans approximately 6-months postdiagnosis. We calculated adjusted geometric means of total body BMD within quartiles (Q) of LM and FM. We also stratified LM-BMD associations by a fat mass index threshold that tracks with obesity (lower body fat: <= 12.9 kg/m(2); higher body fat: > 12.9 kg/m(2)) and stratified FM-BMD associations by appendicular lean mass index level corresponding with sarcopenia (non-sarcopenic: >= 5.45 kg/m(2) and sarcopenic: < 5.45 kg/m(2)). Results: Higher LM (Q4 vs. Q1) was associated with higher total body BMD overall (1.12 g/cm(2) vs. 1.07 g/cm(2), p-trend < 0.0001), and among survivors with lower body fat (1.13 g/cm(2) vs. 1.07 g/cm(2), p-trend <0.0001) and higher body fat (1.15 g/cm(2) vs. 1.08 g/cm(2), p-trend = 0.004). Higher FM (Q4 vs. Q1) was associated with higher total body BMD overall (1.12 g/cm(2) vs. 1.07 g/cm(2), p-trend < 0.0001) and among non-sarcopenic survivors (1.15 g/cm(2) vs. 1.08 g/cm(2), p <0.0001), but the association was not significant among sarcopenic survivors (1.09 g/cm(2) vs. 1.04 g/cm(2), p-trend = 0.18). Conclusion: Among breast cancer survivors, higher LM and FM were independently related to higher total body BMD. Future exercise interventions to prevent bone loss among survivors should consider the potential relevance of increasing and preserving LM.