A randomised controlled trial (RCT) of 56 women with GDM diagnosed at 24–28 weeks gestation randomised to calcium plus 25-OHD (50,000 international units (IU) at baseline and day 21) compared to placebo, found a significant reduction in fasting glucose, serum insulin levels, HOMA-IR, and a significant increase in the quantitative insulin sensitivity index in the intervention group [130]. This evidence concerns the gene INS and gestational diabetes.