It has previously been reported that the influence of vitamin D on the metabolism of calcium and phosphorus is associated with diabetes, cardiovascular disease, Alzheimer's disease, cancer and other systemic diseases, and is considered an important indicator of general health. The present study was conducted to determine the effect of various doses of vitamin D supplementation on glucose metabolism, lipid concentrations, inflammation and the levels of oxidative stress of pregnant women with gestational diabetes mellitus (GDM). The present randomized, double-blind placebo-controlled clinical trial was conducted on 133 pregnant women with GDM during weeks 24-28 of pregnancy. The patients were randomly divided into four groups. The control group (n=20) received a placebo (sucrose; one granule/day), the low dosage group (n=38) received the daily recommended intake of 200 IU vitamin D (calciferol) daily, the medium dosage group (n=38) received 50,000 IU monthly (2,000 IU daily for 25 days) and the high dosage group (n=37) received 50,000 IU every 2 weeks (4,000 IU daily for 12.5 days). The general characteristics and dietary intakes of the patients with GDM were similar between each group. Using ELISA kits, it was determined that insulin, homeostatic model assessment-insulin resistance and total cholesterol were significantly reduced by high dosage vitamin D supplementation (P<0.05). Total antioxidant capacity and total glutathione levels were significantly elevated as a result of high dosage vitamin D supplementation (P<0.01). In conclusion, high-dose vitamin D supplementation (50,000 IU every 2 weeks) significantly improved insulin resistance in pregnant women with GDM.
Keywords: gestational diabetes mellitus; pregnant women; randomized controlled trial; vitamin D supplementation.