Role of vitamin D and vitamin D receptor gene polymorphisms on residual beta cell function in children with type 1 diabetes mellitus.

Abstract

After the onset of type 1 diabetes mellitus (T1DM), preservation of the residual ß-cell function can help good metabolic control. The aim of this study was to evaluate the effect of vitamin D and its receptor gene polymorphisms on residual ß-cells function. One hundred and one children with T1DM (new cases) older than 5 years were selected. Vitamin D receptor (VDR) gene polymorphisms, vitamin D (VD), fasting and stimulated C-peptide (FCP and SCP) levels were measured within 1.5 and 4.5 month after the diagnosis of disease. Kruskal-Wallis and Mann-whitney U test were used for comparing the study groups. Generalized estimating equation (GEE) model was used for the estimation of association between VD and VDR gene polymorphisms with FCP and SCP after adjustment for comorbid variables. The most frequent genotypes and alleles in TaqI, FokI, BsmI and ApaI polymorphisms were TT (50%) and allele T (68.88%), FF (59.2%) and allele F (77.04%), Bb (41.8%) and allele b (61.73%), and Aa (53.1%) and allele A (63.29%) respectively. In children with higher VD levels, the C-peptide (CP) levels were elevated. Also we observed: the tt genotype associated with increasing SCP levels compared with TT genotype; the bb and Bb genotypes were associated with increasing both FCP and SCP in comparison to BB; and the aa and Aa genotypes were associated with decreasing FCP in comparison to the AA genotype. Sufficient levels of VD (more than 30 ng/ml) can preserve residual ß-cells and insulin secretion.