Vitamin D Receptor Gene Polymorphisms, β-cell Function, and Vitamin D Status in Non-obese Mexican Adults

Abstract

FokI (rs2228570 T>C) and BsmI (rs1544410 A>G) polymorphisms of the vitamin D receptor (VDR) have been associated to abnormal glucose metabolism and could be inversely associated with β-cell function (BCF) and vitamin D status. There is a lack of information about this topic in the Mexican population. To evaluate the relationship between VDR gene polymorphisms FokI and BsmI with BCF and vitamin D status in a population of non-obese Mexican adults. A sample of 192 participants were enrolled during 2016-2018. Blood samples were collected to determine fasting concentrations of glucose, insulin, and vitamin D. Genomic DNA was isolated from leucocytes and the polymorphic variants of FokI and BsmI were analyzed. The Homeostasis Model Assessment Calculator was used to estimate the BCF (HOMA2-B). FokI polymorphism showed a frequency of 20.1% for homozygous TT carriers and 7.8% for the BsmI GG. The recessive model of FokI (TT genotype) showed a lower mean value of BCF compared to the combination of CC+CT (99.2 vs. 109.6%, p=0.045). Likewise, significantly lower mean values of HOMA2-B and insulin were observed for BsmI (GG genotype, p=0.016 and p=0.039, respectively). After covariates adjustment, only FokI polymorphism remained as an independent predictor of BCF. the TT and GG variants of the FokI and BsmI polymorphisms are related to a decrease in FCB. In the case of FokI, this decrement was independent of insulin sensitivity, vitamin D levels, percentage of body fat, gender, and age.