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