Visceral Fat Is a Negative Predictor of Bone Density Measures in Obese Adolescent Girls

The accumulation of adipose tissue in 2 regional fat depots, visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT), have a differential impact on bone mineral density (BMD). In most studies, a positive association of SAT with bone density has been reported. There are conflicting data on the effect of VAT on bone. One recent study suggested that VAT was a negative and SAT a positive predictor of bone structural parameters in young adults. Various chemicals secreted from VAT and SAT appear to mediate these associations with bone but there is a limited knowledge of their role. Potential mediators include inflammatory cytokines such as IL-6, soluble intercellular adhesion molecules such as E-selectin, and adipokine hormones such as adiponectin and leptin. IL-6 and adiponectin can increase osteoclast activity and appear to have deleterious effects on BMD. In a previous report, VAT was an independent predictor of E-selectin and soluble intercellular adhesion molecule I (sICAM1), whereas SAT was a predictor of IL-6, and both SAT and VAT predicted adiponectin levels. Other studies have shown that VAT is an important determinant of levels of sICAM1 and E-selectin in obese and normal-weight girls. This cross-sectional study investigated associations of VAT and SAT and potential chemical mediators with BMD in adolescent obese and normal-weight girls. The investigators tested the hypothesis that adolescent girls with a greater VAT to SAT ratio would have lower bone density measures mediated by inflammatory cytokines, adiponectin, and leptin. Fifteen obese girls 12 to 18 years old were matched to 15 normal-weight controls for race, ethnicity, and bone age (within 2 year). Magnetic resonance imaging was used to measure SAT and VAT at the lumbar level. Dual-energy x-ray absorptiometry assessed bone density at the spine, hip, and whole body. Fasting serum levels of leptin, adiponectin, E-selectin, sICAM, and IL-6 were determined. The mean body mass index SD score was higher in obese subjects than in controls (3.7 ± 1.5 versus 0.1 ± 0.4 kg/m 2 ). After controlling for SAT, VAT was a negative predictor of whole-body BMD and bone mineral content/height in the whole group, and of BMD, bone mineral apparent density, whole-body BMD, and bone mineral content/height in obese girls. As hypothesized, obese girls with the highest VAT to SAT ratio had the lowest bone density measures. E-selectin and adiponectin were negative predictors for BMD, and leptin was a positive predictor in a regression model including VAT/SAT, adipokines, and cytokines. These findings indicate that VAT is a negative predictor of bone density in obese girls. Pro-inflammatory adhesion molecules such as E-selectin and adipokines such as adiponectin and leptin appear to mediate the association between VAT and bone density.