Vitamin D-binding protein and 25-hydroxyvitamin D during pregnancy in mothers whose children later developed type 1 diabetes.

Background Levels of 25-hydroxyvitamin D (25-OH D) during late pregnancy have been linked to type 1 diabetes risk in the offspring. Vitamin D-binding protein increases in concentration during pregnancy. We aimed to test whether concentrations of vitamin D-binding protein and 25-OH D throughout pregnancy differed between women whose offspring later developed type 1 diabetes (cases) and controls. Methods A nested case-control study was conducted within a cohort of pregnant women from all over Norway in 1992-1994. Offspring registered in The Norwegian Childhood Diabetes Registry, diagnosed with type 1 diabetes before age 15, defined the case women, giving 113 cases in the study. Two hundred twenty controls were randomly selected within the same cohort. One to four serum samples from each participant drawn at different time points during pregnancy were analysed for vitamin D-binding protein and 25-OH D by radioimmunoassay. Results Vitamin D-binding protein and 25-OH D significantly increased by gestational week (p < 0.001) and tended to be lower in cases than in controls, -0.27 mu mol/L (95% CI -0.57, 0.03) and -5.01 nmol/L (95% CI -8.03, -0.73), respectively. While first and second trimester concentrations of vitamin D-binding protein and 25-OH D alone were not significantly different, lower third trimester concentrations tended to be associated with higher risk of type 1 diabetes in the offspring, albeit at borderline significance after mutual adjustment. Conclusions In this first study of maternal vitamin D-binding protein measured throughout pregnancy and risk of type 1 diabetes in offspring, lower concentration, particularly in the third trimester, tended to be associated with type 1 diabetes. Copyright (C) 2016 John Wiley & Sons, Ltd.