Poster Presentation The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2017

Insulin sensitivity, 25-hydroxyvitamin D and phosphate levels and not calcium levels are determinants of bone mineral density in overweight and obese individuals.  (#195)

Negar Naderpoor 1 2 , Aya Mousa 1 , Barbora de Courten 1 2
  1. Monash Centre for Health Research and Implementation, School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia
  2. Diabetes Unit, Monash Health, Melbourne , VIC

Introduction: Obesity and higher 25-hydroxyvitamin D (25OHD) levels are known to be associated with higher bone mineral density (BMD). Obese individuals, despite higher BMD, are at higher risk of vitamin D deficiency. There is limited data on other factors influencing BMD in the obese population. Furthermore, while the negative effect of low calcium intake on bone health is well-established, few studies have investigated whether serum calcium concentrations within the normal range are related to BMD.

Methods: We examined the relationships between BMD and anthropometric (BMI, % body fat, fat mass and fat-free mass) and biochemical markers (parathyroid hormone [PTH], 25OHD, calcium and phosphate, alkaline phosphatase [ALP], high-sensitivity C-reactive protein [hs-CRP]), in addition to insulin sensitivity (euglycaemic-hyperinsulinaemic clamp, M-value), lipid profile, dietary calcium and phosphate intake and physical activity in 54 overweight or obese but otherwise healthy adults with 25OHD≤50 nmol/L.  

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 and PTH levels between insulin-sensitive and insulin-resistant groups (M-value cut-off of 4.7 mg/kg/min, all p>0.5). However, ALP was significantly higher in the insulin resistant group (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. BMD was not related to calcium, PTH, dietary calcium or phosphate, physical activity, PFAT, fat mass and lean mass (all p>0.05). 

Conclusion: Insulin sensitivity and phosphate levels in addition to BMI and 25OHD were independent determinants of BMD in this overweight/obese and vitamin D deficient population. These findings highlight the independent effect of insulin sensitivity on bone health and suggest that in normal physiological ranges, serum phosphate concentration is a better predictor of BMD than serum calcium concentration.