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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

New RCT finds vitamin D may help women with gestational diabetes

A new study published in American Journal of Clinical Nutrition has found that vitamin D supplementation may improve some aspects of metabolic function in women with gestational diabetes.

While research on vitamin D’s role in type 1 and type 2 diabetes is extensive, there hasn’t been much research on whether vitamin D plays a role in gestational diabetes. Gestational diabetes is a type of diabetes that occurs in women during pregnancy. Results from a few observational studies suggest vitamin D plays a role in gestational diabetes, but randomized controlled trials in this area are lacking.

It is important to study vitamin D and gestational diabetes separately from other forms of diabetes because gestational diabetes increases the risk of having a complicated birth and of developing conditions during pregnancy such as preeclampsia and metabolic syndrome.

Researchers from the Kashan University of Medical Sciences and the Isfahan University of Medical Services in Iran recently conducted the first randomized controlled trial that aimed to see if vitamin D might be able to improve some aspects of gestational diabetes.

The researchers recruited 54 women who were all in the end of their second trimester of pregnancy at 24-28 weeks gestation. The women were randomly assigned to a vitamin D group or a placebo group. The women in the vitamin D group received 50,000 IU of vitamin D3 twice during the 6 week study, once at the start of the trial and again at 3 weeks. The women in the placebo group received a placebo at the same intervals.

The researchers measured vitamin D levels, certain markers of metabolic function, insulin function, and inflammation at baseline and again at the end of the trial at 6 weeks.

The markers of metabolic function included fasting plasma glucose, total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides. Low levels of every marker besides HDL and high levels of HDL cholesterol indicate a healthier metabolism.

The markers of insulin function included homeostatic model assessment of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), and total serum insulin concentration. HOMA-IR and QUICKI are methods used to assess how the body responds to insulin. A lower HOMA-IR and a higher QUICKI are indicators of better insulin function.

Finally, the markers of inflammation included C-reactive protein (CRP), total anti-oxidant capacity (TAC), and plasma total glutathione (GSH). Both TAC and GSH are indicators of oxidative stress, with high levels of both indicating lower oxidative stress. Oxidative stress can lead to inflammation and occurs when the body is not able to remove harmful, unstable oxygen molecules.

The researchers were interested in whether vitamin D supplementation would improve these markers and therefore improve aspects of gestational diabetes in these women.

After 6 weeks, 3 women from the vitamin D group and 3 women from the placebo group were excluded. The researchers did an intention-to-treat analysis, meaning that despite these women being excluded, the researchers still included them in their analysis of the effectiveness of vitamin D vs. placebo.

Here is what the researchers found:

  • In the vitamin D group, average vitamin D levels increased from 20.44 ng/ml to 38.95 ng/ml. There was no change in vitamin D levels in the placebo group.
  • The vitamin D group experienced significant reductions in fasting blood glucose, total cholesterol, and LDL cholesterol compared to the placebo group. There was no significant change in triglycerides or HDL cholesterol.
  • The vitamin D group experienced a significant reduction in serum insulin concentration, HOMA-IR and a significant increase in QUICKI compared to the placebo group.
  • There were no significant changes in any markers of inflammation in either group.

The researchers concluded,

“Our study showed that vitamin D supplementation in pregnant women with [gestational diabetes] resulted in improved glycemic status and a significant decrease in serum total and LDL-cholesterol concentrations but did not affect other lipid profiles, hs-CRP, plasma TAC, or GSH concentrations.”

While the results indicate that vitamin D did not affect markers of inflammation, the researchers did note that they didn’t measure all markers of inflammation or oxidative stress. Therefore we can’t be certain about the effects of vitamin D on inflammation. Furthermore, the study is limited by its small sample size and the relatively small doses of vitamin D used.

The results suggest that vitamin D does play a role in gestational diabetes. We need larger randomized controlled trials that use larger doses to be able to determine the role that vitamin D plays in gestational diabetes.


Asemi, Z. et al. Effects of vitamin D supplementation on glucose metabolism, lipid concentrations, inflammation, and oxidative stress in gestational diabetes: a double-blinded randomized controlled clinical trial. American Journal of Clinical Nutrition, 2014.

  About: Jeff Nicklas

Jeff Nicklas was a staff member for the Vitamin D Council from October 2013 to January 2015. He is now pursuing his passion for public health through graduate studies.