Effect of vitamin D on insulin resistance and nephropathy in type 2 diabetes

| June 2014 | 581 HbA1c concentration in male interventional group is signifi cantly less than that of the control group.[7] We concluded that weekly vitamin D supplementation had benefi cial eff ects on glycemic parameters in male T2DM patients.[6] Study regarding the glycemic control of vitamin D revealed diff erent results. Recently, in a study conducted by Huang et al., the diff erence in vitamin D levels between those with micro-and those with macro-albuminuria was examined.[7] They also aimed to determine whether low dose of cholecalciferol was able to ameliorate albuminuria. They conducted two investigations; a cross-sectional study of patients with T2DM and healthy controls and a longitudinal study on T2DM patients with albuminuria treated with conventional dose (800 IU) of cholecalciferol for 6 months.[7] In the fi rst study, compared to controls and T2DM patients with normoalbuminuria, the serum 25 (OH) D3 level was signifi cantly lower in patients with macro-albuminuria, but not in patients with microalbuminuria. They detected that plasma 25 (OH) D3 level was independently associated with micro-albuminuria. In their longitudinal investigation, they found that cholecalciferol effi ciently decreased micro-albuminuria in the early stages of treatment in conjunction with an increase in serum 25 (OH) D3 level.[7] They interpreted that conventional doses of cholecalciferol might have an anti-proteinuric eff ect on Chinese T2DM patients with nephropathy.[7] Furthermore, they found that a low vitamin D status was more closely associated with micro-albuminuria in male subjects than in female ones.[7] Limitations of the study conducted by Heshmat et al. need to be considered, too. The sample size was small and the duration of drug therapy was short. Notably, the season may aff ect vitamin D level and also may have an impact on the treatment outcome, a factor that is very diffi cult to control.[7-10] In addition, the best eff ective dose requires further investigation.[10-14] Lastly, the lack of assessment of parathormone level is a defi cit. There is an evidence revealing the positive association of parathyroid hormone and level of blood pressure as a perturbing factor for diabetic nephropathy.[2-9,15-18] Thus, the negative result on improving diabetes control and insulin resistance should not discourage its use. We suggest more prospective interventional investigations with longer duration with control of confounders to be er detect this aspect of diabetic patients. Furthermore, it should be reminded that the most eff ective dose of vitamin D requires further examination.