Associations of serum vitamin D concentrations with obstetric glucose metabolism in a subset of the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study cohort

Diabet. Med. 29, e199–e204 (2012) Abstract Aims  To assess associations between maternal serum vitamin D concentration and glucose metabolism in a cohort of pregnant women living in an Australian subtropical environment. Methods  Cross‐sectional assessment of 25‐hydroxy vitamin D concentrations in 399 Hyperglycemia and Adverse Pregnancy Outcome ancillary study participants, treated at an obstetric teaching hospital in Brisbane, Australia. All patients underwent a blinded 75‐g oral glucose tolerance test at 24–32 (target 28) weeks’ gestation. Results  The mean (± standard deviation) fasting plasma glucose was 4.5 ± 0.4 mmol/l. Mean (± standard deviation) serum 25‐hydroxy vitamin D was 132.5 ± 44.0 nmol/l. A difference of one standard deviation in maternal 25‐hydroxy vitamin D was inversely related to fasting glucose (fasting glucose lower by 0.047 mmol/l, P  = 0.012) when assessed with multiple linear regression after adjusting for confounders. Maternal 25‐hydroxy vitamin D correlated with β‐cell function as estimated by the log‐transformed homeostasis model assessment–β‐cell function equation ( r  = 0.131, P  = 0.009), but not with the homeostasis model assessment of insulin resistance. Conclusions  An association between mid‐gestational 25‐hydroxy vitamin D and fasting glucose was confirmed in a largely normoglycaemic and vitamin D‐replete pregnant population. The correlation between 25‐hydroxy vitamin D and β‐cell function suggests that vitamin D may influence glucose metabolism through this mechanism. Intervention studies are required to determine causality and the role of vitamin D replacement in deficient individuals.