Abstract
Vitamin D is involved in glucose homeostasis and in the mechanisms underlying insulin release. Vitamin D deficiency increases the risk of many diseases, including type 2 diabetes and osteoporosis. Serum 25-hydroxy vitamin D (25-OH-D) is an important determinant of bone health. We assessed vitamin D status in postmenopausal diabetic and non-diabetic Saudi women and determined the incidence of low bone mineral density (BMD) in relation to bone mass index (BMI) and bone turnover markers (BTMs). Postmenopausal Saudi women (n 98) aged 50-80 years living in Jeddah, Saudi Arabia were divided into diabetic (n= 53) and nondiabetic (n= 45) groups. Serum levels of intact parathyroid hormone (IPTH), 25-OH-D, glucose, insulin and BTMs were measured. BMD was measured by dual-energy X-ray absorptiometry (DEXA) at the lumbar spine, total hip and femur neck. We observed that 86.0% of the diabetic group and 81% of the non-diabetic group were vitamin D-deficient [25-OH-D < 50.0 nmol/L (20 ng/ml)]. The BMD at lumbar spine was significantly lower in diabetic overweight (0.96 +/- 0.13 g/cm2) compared to diabetic obese (1.05 +/- 0.17 g/cm2) p = 0.05, and significantly lower in non-diabetic overweight (0.93 +/- 0.14 g/cm2) compared to diabetic obese (1.05 +/- 0.17 g/cm2) p=.013. The women were further divided into four subgroups according to their diabetes diagnosis and BMI >= 30 Kg/m2 for obese, and BMI 25-29.9 Kg/m2 for overweight. Serum 25-OH-D level was inversely related to PTH in diabetic obese. BMD at lumbar spine in non-diabetic obese was significantly positively correlated with BMI and with 25-OH-D in the same subgroup. Markers of bone turnover (osteocalcin (OC) and C-terminal telopeptide (CTx) were significantly negatively correlated with 25-OH-D in both the diabetic overweight and non-diabetics overweight. In conclusion, low vitamin D levels contribute to osteoporosis and diabetes complications in postmenopausal Saudi women, and the effects of vitamin D on cortical bone were different from the effects on cancellous bone. The BMD results suggested that osteoporosis was more common among these diabetic women and certainly warrants further investigation.