Effects of vitamin D supplementation on glucose metabolism, lipid concentrations, inflammation, and oxidative stress in gestational diabetes: a double-blind randomized controlled clinical trial.

Randomized, double-blind, placebo-controlled clinical trial in pregnant women with gestational diabetes mellitus in Kashan, Iran. Participants were 18 to 40 years old and enrolled at 24 to 28 weeks of gestation; 54 women were randomized in total, with 27 assigned to the vitamin D arm and 27 to placebo.

Vitamin D3 (cholecalciferol) was given as 50,000 IU oral capsules, with two administrations during the 6-week trial, at baseline and on day 21. The active arm received D-Vitin 50000; the placebo capsules were identical in appearance. In the vitamin D group, 27 participants were randomized and 24 completed the study.

Vitamin D supplementation improved glycemic status and lowered total cholesterol and LDL cholesterol, but did not improve triglycerides, HDL cholesterol, inflammation, or oxidative stress markers. Compared with placebo, the vitamin D group had greater increases in 25(OH)D (+18.5 6 20.4 ng/mL vs +0.5 6 6.1 ng/mL; P < 0.001), greater reductions in fasting plasma glucose (−17.1 6 14.8 mg/dL vs −0.9 6 16.6 mg/dL; P < 0.001), insulin (−3.08 6 6.62 mIU/mL vs +1.34 6 6.51 mIU/mL; P = 0.01), HOMA-IR (−1.28 6 1.41 vs +0.34 6 1.79; P < 0.001), total cholesterol (−11.0 6 23.5 mg/dL vs +9.5 6 36.5 mg/dL; P = 0.01), and LDL cholesterol (−10.8 6 22.4 mg/dL vs +10.4 6 28.0 mg/dL; P = 0.003). QUICKI also improved (+0.03 6 0.03 vs −0.001 6 0.02; P = 0.003). Adjusted analyses were similar except that the fasting glucose and calcium findings were no longer significant.

The intervention period was short at 6 weeks and the active-arm sample was small, limiting precision and longer-term inference. Several outcomes were unchanged, and adjusted analyses attenuated the fasting glucose result. Generalizability is limited to pregnant women with gestational diabetes in one Iranian setting, and physical activity was not measured objectively.