Aims Vitamin D deficiency has been linked to impaired glucose metabolism. We determined whether serum 25-hydroxyvitamin D (25OHD) is associated with glucose metabolism in pregnant women and the effect of ethnicity on this relationship.
Methods We analysed serum 25OHD concentrations in 307 pregnant women attending a metropolitan obstetric clinic between October 2003 and May 2005. Measurements from 264 of the women were taken at the time of glucose tolerance testing at mid-gestation, a population therefore at increased risk for gestational diabetes. Pearson correlation analysis was used to test for univariate linear relationships between the natural log of serum 25OHD (ln-25OHD) and other variables. Multiple regression analysis was used to adjust for confounding factors.
Results Mean serum 25OHD concentration was 53.8 ± 23.9 nmol/l (sd). Ln-25OHD was negatively correlated with serum parathyroid hormone as expected (r −0.24, confidence intervals −0.35 to −0.12). Ln-25OHD was also negatively correlated with fasting plasma glucose (r−0.20, −0.31 to −0.08), fasting insulin (r −0.20, −0.31 to −0.08) and insulin resistance as calculated by homeostatis model assessment (r −0.21, −0.32 to −0.09). The association between fasting glucose and log-transformed 25OHD concentration was of borderline significance after accounting for ethnicity, age and body mass index in multivariate analyses (−0.13, −0.26 to 0.01). The odds ratio of gestational diabetes in women with 25OHD < 50 nmol/l did not reach statistical significance (1.92, 95% confidence interval 0.89–4.17).
Conclusions Maternal 25OHD concentrations are inversely related to fasting glucose, although further studies are required to establish whether this is independent of the effects of ethnic background.