Glucose homeostasis, beta cell function, and insulin resistance in relation to vitamin D status after gestational diabetes mellitus

Introduction. We wanted to determine vitamin D status after gestational diabetes mellitus (GDM) and to evaluate whether levels of 25-hydroxyvitamin D-3 (25OHD(3)) are associated with beta cell function, insulin resistance or a diagnosis of diabetes after GDM. Material and methods. Glucose homeostasis was assessed during a 75-g oral glucose tolerance test one to two years after delivery in 376 women with previous GDM (287 European and 78 non-European, including 33 Arab and 35 Asian women). Insulin resistance was estimated using homeostasis model assessment of insulin resistance (HOMA-IR). The insulinogenic index (I/G30) and the disposition index [(I/G30)/HOMA-IR] were used to calculate insulin secretion. Concentrations of serum 25OHD3 were determined. Results. Mean (+/- SD) 25OHD3 concentration was 50.0 +/- 22.3 nmol/L and differed significantly among subgroups of body mass index, ethnicity, and glucose tolerance status; 53% had 25OHD(3) levels <50 nmol/L and 87% had 25OHD(3) levels <75 nmol/L. There was a negative correlation between 25OHD(3) concentration and HOMA-IR (p < 0.001) and a positive correlation between 25OHD(3) and disposition index (p = 0.002) in univariable regression analysis. Correlations attenuated after adjustment for body mass index. In univariable regression analysis, 25OHD(3) concentrations were significantly associated with diabetes after GDM (p = 0.004). However, in a multivariable model, non-European origin, HOMA-IR and insulinogenic index were significantly associated with postpartum diabetes, whereas 25OHD(3) concentrations were not. Conclusion. Vitamin D deficiency/insufficiency in previous GDM cases appears to be associated with beta cell dysfunction and insulin resistance, but not with postpartum diabetes when factors well known to influence type-2 diabetes were adjusted for.