Insulin Sensitivity Is an Independent Determinant of Bone Mineral Density in Overweight and Obese Individuals

Background: Higher BMI and 25-hydroxyvitamin D (25OHD) levels are associated with higher bone mineral density (BMD). However, obese individuals are more likely to be vitamin D-deficient. There is limited data on other factors influencing BMD in the obese population.

Methods: We examined the cross-sectional relationship between BMD and anthropometric, metabolic, biochemical markers, in addition to dietary calcium and phosphate intake and physical activity in 54 overweight or obese but otherwise healthy adults (35 males, 19 females) with 25OHD≤50 nmol/L. BMD, body mass index (BMI), percent body fat (PFAT), fat mass and lean mass (dual energy x-ray absorptiometry), insulin sensitivity (euglycaemic-hyperinsulinaemic clamp, M), 25OHD, calcium and phosphate, PTH, FGF-23, alkaline phosphatase (ALP), high-sensitivity C-reactive protein (hs-CRP), lipid profile were measured and physical activity and dietary calcium and phosphate intake were calculated based on self-report and validated questionnaires.

Results: BMD was correlated with 25OHD (r=0.3, p=0.02), phosphate (r=0.3, p=0.04), M (r=0.4, p=0.006), dietary calcium (r=0.3, p=0.3) and dietary phosphate (r=0.3, p=0.04) after adjustments for age, sex and BMI. There were no differences in BMD, 25OHD, calcium, phosphate, PTH and FGF-23 levels between insulin-sensitive and insulin-resistant groups (insulin sensitivity (M) cut-off of 4.7 mg/kg/min, all p>0.5). However, ALP was significantly higher in the insulin-resistant group (86.28 vs. 72.92 IU/L, p=0.04). In regression analyses, 25OHD (p=0.02), phosphate (p=0.01), BMI (p=0.02) and M (p=0.02) remained independently related to BMD.

Conclusion: Insulin sensitivity and phosphate levels in addition to BMI and 25OHD were related to BMD in this overweight/obese and vitamin D-deficient population. These findings provide further evidence supporting an independent role for insulin sensitivity in bone health.