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 homeostasis 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.