Lean Mass Appears to Be More Strongly Associated with Bone Health than Fat Mass in Urban Black South African Women.

OBJECTIVES: To examine the association between body composition (fat mass, lean mass and body mass index, BMI) and bone health (bone mineral density, BMD and fracture risk) in urban black South African women. DESIGN: A cross sectional study examining associations between body composition, dietary intake (food frequency questionnaire), habitual physical activity (Activity energy expenditure (AEE) measured using an accelerometer with combined heart rate monitor and physical activity questionnaire) and bone health (BMD using dual-energy X ray absorptiometry, DXA and fracture risk). SETTING: Urban community dwellers from Ikageng in the North-West Province of South Africa. PARTICIPANTS: One hundred and eighty nine (189) healthy postmenopausal women aged ≥43 years. RESULTS: Fat mass and lean mass were significantly associated with BMD and fracture risk when adjusted for potential confounders. However, lean mass and not fat mass remained significantly associated with femoral neck BMD (ß = 0.49, p <0.001), spine BMD (ß = 0.48, p< 0.0001) and hip BMD (ß = 0.59, p< 0.0001). Lean mass was also negatively associated with fracture risk (ß = -0.19 p =0.04) when both lean and fat mass were in the same model. CONCLUSION: Lean mass and fat mass were positively associated with femoral neck, spine and hip BMDs and negatively associated with fracture risk in urban black South African women. Our finding suggests that increasing lean mass rather than fat mass is beneficial to bone health. Our study emphasises the importance of positive lifestyle changes, intake of calcium from dairy and adequate weight to maintain and improve bone health of postmenopausal women.

Ethnic-specific cut-points for sarcopenia: evidence from black South African women.

BACKGROUND/OBJECTIVES: Age-related muscle and fat mass (FM) changes are ethnicity specific. We aimed to develop a cut-point for the muscle mass component of sarcopenia for black South African (SA) women, and to assess its predictive value, in comparison to established cut-points, to identify functional ability among older black SA women. SUBJECTS/METHODS: In a cross-sectional study, a sarcopenia cut-point was calculated from dual energy X-ray absorptiometry (DXA)-derived appendicular skeletal muscle mass (ASM) indexes (ASMI) from two young black SA reference groups. The new cut-point was compared with the most recent Foundation for the National Institutes of Health (FNIH) criteria (ASM <15.02 kg; and ASM(BMI) <0.512), an internationally accepted cut-point (ASMI <5.5 kg/m(2)) and a residual method adjusting for FM. All cut-points were then applied to 221 older black women to predict gait speed and handgrip strength. RESULTS: A cut-point of ASMI <4.94 kg/m(2) was derived from the young SA reference groups. Using this cut-point, 9.1% of older women were classified as sarcopenic, compared with 16.7-38.7% using other cut-points. The only cut-points that significantly predicted low functional ability (low gait speed and low handgrip strength) in older black women were the new SA cut-point and the FNIH ASM criterion. Multivariate logistic regression models for both these cut-points significantly predicted low handgrip strength (odds ratio (OR)=3.71, P=0.007 and OR=3.42, P=0.001, respectively) and low gait speed (OR=9.82, P=0.004 and OR=8.71, P=0.008, respectively). CONCLUSIONS: The new SA cut-point had similar or greater odds of predicting reduced functional ability in older SA women when compared with other internationally accepted cut-points.