Independent relationships between bone mineral density, regional body fat and insulin sensitivity in white males.

ABSTRACT

BACKGROUND: Adiposity and insulin sensitivity may affect bone mineral density (BMD), but the confounding effect of weight hinders discrimination of independent associations. We explored whether regional fat masses and insulin sensitivity are independently related to BMD. MATERIALS AND METHODS: Relationships between total and regional body fat, insulin sensitivity and measures of BMD in 8 different regions were evaluated in a cross section of 590 generally healthy, white males, 274 of whom received measurement of insulin sensitivity (Si) using the intravenous glucose tolerance test. Measurements included total, android and gynoid fat and lean body mass and regional BMDs by dual-energy X-ray absorptiometry. Linear regression analyses were combined in a mediation analysis to explore associations with each regional BMD. RESULTS: Weight correlated positively with total fat mass (R2  = 0.67, P < 0.001) and negatively with Si (R2  = 0.14, P < 0.001). Body composition measures were consistently positively related to BMD in all regions except lumbar and thoracic spine. Accounting for body weight rendered negative majority of associations between total and regional fat masses and BMDs. An independent association between android fat and spine BMD was particularly apparent. Si was positively associated with total and limb BMD (P < 0.01) specifically among exercisers. Accounting for Si diminished the associations of total fat (negative) and lean body mass (positive) with total and limb BMD. CONCLUSION: Android fat is independently negatively associated with spine BMD. Among those taking exercise, increased insulin sensitivity is associated with higher limb BMD and may underlie positive associations between lean body mass and BMD.