Effects of a single post-partum injection of a high dose of vitamin D on glucose tolerance and insulin resistance in mothers with first-time gestational diabetes mellitus.

Aim This study was performed to determine the effect of a single, large, intramuscular injection of vitamin D post-partum on glucose tolerance and insulin resistance in women with gestational diabetes. Methods Forty-five participants in a randomized controlled trial on gestational diabetes mellitus were divided into an intervention group and a control group. Only subjects in the intervention group received one intramuscular injection of 300 000 IU of vitamin D3. HbA1c, serum 25-hydroxyvitamin D3, fasting insulin and blood glucose, C-peptide, homeostasis model assessment insulin resistance index (HOMA-IR), beta-cell function, insulin sensitivity and the Quantitative Insulin Sensitivity Check Index (QUICKI) were measured at baseline and after 3 months of intervention. Results Approximately 80% of the mothers had a degree of vitamin D deficiency. Post-intervention, this was found in 4.2 and 71.4% in the intervention and control groups, respectively. The medians of HOMA-IR indices before and after intervention were 0.6 and 0.5 (P = 0.7), respectively, in subjects in the intervention group, and 0.5 and 0.9 (P = 0.01) in subjects in the control group. The mean of the QUICKI fell only in the control group (P = 0.008). In the control group, beta-cell function increased by similar to 8% (P = 0.01) and insulin sensitivity decreased after 3 months (P = 0.002). Post-intervention, the median C-peptide decreased in the intervention group and increased in the control group, but the change was significant only in the control group (P = 0.03). Conclusions A single injection of 300 000 IU of vitamin D3 achieves a 3-month serum 25-hydroxyvitamin D range of 5080 nmol/l and is an efficient, effective and safe procedure for improving the vitamin status and indices of insulin resistance in mothers with gestational diabetes after delivery.