The relationship between body composition and bone mineral content: threshold effects in a racially and ethnically diverse group of men

Abstract

We examined BMC and body composition in 1,209 black, Hispanic, and white men. Weight, BMI, waist circumference, and fat mass were associated with BMC only up to certain thresholds, whereas lean mass exhibited more consistent associations. The protective influence of increased weight appears to be driven by lean mass.

Introduction: Reduced body size is associated with decreased bone mass and increased fracture risk, but associations in men and racially/ethnically diverse populations remain understudied. We examined bone mineral content (BMC) at the hip, spine, and forearm as a function of body weight, body mass index (BMI), waist circumference, fat mass (FM), and nonbone lean mass (LM).

Methods: The design was cross-sectional; 363 non-Hispanic black, 397 Hispanic, and 449 non-Hispanic white residents of greater Boston participated (N = 1,209, ages 30-79 y). BMC, LM, and FM were measured by DXA. Multiple linear regression was used to describe associations.

Results: Weight, BMI, waist circumference, and FM were associated with BMC only up to certain thresholds. LM, by contrast, displayed strong and consistent associations; in multivariate models, femoral neck BMC exhibited a 13% increase per 10 kg cross-sectional increase in LM. In models controlling for LM, positive associations between BMC and other body composition measures were eliminated. Results did not vary by race/ethnicity.

Conclusions: The protective effect of increased body size in maintaining bone mass is likely due to the influence of lean tissue. These results suggest that maintenance of lean mass is the most promising strategy in maintaining bone health with advancing age.

Fig. 1

Bone mineral content (BMC) versus body mass index (BMI) and lean mass, by skeletal site. Semiparametric scatter-plot smooths (black lines) indicate that BMI displays a positive association with BMC up to approximately 35 kg/m², whereas the association between total lean mass and BMC is positive over the entire range of lean mass values. The association between BMC and body composition is weaker at the wrist than at other sites

Fig. 2

Femoral neck BMC versus body shape and composition. Unadjusted associations (black lines, estimated using semiparametric scatterplot smooths) are well approximated by linear spline models (gray lines) with single knots at 35 kg/ m², 110 cm, 30 kg for BMI, waist circumference, and fat mass, respectively. A single linear trend accurately describes the association between total lean mass and BMC (lower right panel)

Fig. 3

Femoral neck BMC versus proportionate lean mass. There is little marginal association (thick line). However, when subjects are grouped according to BMI (kg/m²), the sharper association between lean mass and BMC becomes clear (thin lines)