Does insulin resistance in type 2 diabetes alter vitamin D status?

Data on changes of vitamin D due to insulin resistance are conflicting. We assessed vitamin D concentrations and parameters of glycemia and mineral homeostasis in patients with insulin resistant type 2 diabetes and in matched normal controls.

Sixty-nine patients with type 2 diabetes and 60 matched normal control subjects were studied. After an overnight fast, blood was collected for measuring the parameters of glycemia (glucose, insulin and HbA1c), mineral profile (corrected calcium, phosphate and alkaline phosphatase), total 25(OH) vitamin D and parathyroid hormone (PTH) levels.

Patients had significantly elevated fasting glucose (P=0.0001), insulin (P=0.0003) and HbA1c (P=0.0005) than the controls had. They had significantly raised calculated insulin resistance compared with control subjects (P=0.0001). Patients and controls had similar levels of serum corrected calcium and ALP, whereas serum phosphate was significantly lower in the patients compared with controls (P=0.001). Patients and controls had similar levels of 25(OH)D, but the levels of 25(OH)D in both were in the deficiency range. Intact PTH was similar in the patients and controls. Levels of 25(OH)D did not demonstrate any relation with fasting insulin, insulin resistance, or HbA1c, but correlated negatively with intact PTH (r=-0.4, P=0.02).

This study demonstrated prevalent vitamin D deficiency in insulin resistant type 2 diabetic and normal subjects. Insulin resistance did not influence the status of vitamin D.