High doses of vitamin D may have beneficial effects on the metabolic parameters of pregnant women with gestational diabetes mellitus.
The randomized controlled trial measured parameters of glucose metabolism in 54 pregnant women with gestational diabetes mellitus (GDM) who received either vitamin D3 (50,000 IU) or a placebo at the beginning of the study and again after three weeks (1). The study results showed that after six weeks the women treated with vitamin D demonstrated a decrease in concentrations of fasting glucose and serum insulin, an improved insulin resistance, as well as reduced levels of LDL-cholesterol compared to placebo. No effect of vitamin D supplementation on biomarkers of oxidative stress was found.
The researchers commented that earlier observational studies indicated a significant association of low serum vitamin D concentrations and a higher incidence of GDM (2). In addition, favorable effects of vitamin D supplementation on glucose homeostasis and insulin sensitivity have been shown in non-pregnant healthy women (3). The beneficial effects of vitamin D on improved insulin action might be explained by its effect on calcium and phosphorus metabolism and through upregulation of the insulin receptor genes (4). The pre- sence of vitamin D receptors in skeletal muscle along with the fact that vitamin D3 increases transcription of insulin receptor genes might further explain the effects of vitamin D on insulin resistance. GDM is associated with serious adverse complications including preeclampsia, higher rates of cesarean section, and increased long-term risk of developing metabolic syndrome and type 2 diabetes mellitus (2).