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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: Vitamin D decreases insulin resistance during pregnancy

Insulin resistance is a state of reduced tissue response to the effect of insulin on blood sugar metabolism. Insulin resistance triggers higher insulin levels. Glucose can’t get into the cells, a usual function of insulin, so higher and higher levels of insulin are needed.

In general, normal pregnancy is associated with insulin resistance. However, insulin resistance is much worse in pregnant women with gestational diabetes, a condition that affects 10% of pregnancies.  No one knows why pregnancy is associated with insulin resistance.

Gestational diabetes usually, but not always, disappears after the pregnancy is over. Since gestational diabetes affects up to 10% of pregnancies, some scientists think it may be a natural phenomenon.

Recently, in a randomized controlled trial out of the Yazd Diabetes Research Center in Iran, scientists have discovered that 50,000 IU of D3 given every two weeks from week 12 of the pregnancy to birth results in significantly less insulin resistance.

Soheilykhah S, et al. The effect of different doses of vitamin D supplementation on insulin resistance during pregnancy. Gynecol Endocrinol. 2013 Apr;29(4):396-9.

One-hundred twenty pregnant women were randomized to be administered 200 IU per day (group A), 50,000 IU per month (group B), or 50,000 IU per every two weeks (group C). The women took the vitamin D from 12 weeks of pregnancy until delivery. Forty patients from group C, 38 patients from group B and 35 patients from group A completed participation. The mean age was 26 years, the mean BMI before pregnancy was 25 and the mean initial 25(OH)D of the pregnant women was around 8 ng/ml.

25(OH)D increased in the 50,000 IU/2 weeks group from 7 to 34 ng/ml; from 7 to 27 ng/ml in the 50,000 IU/month group, and, surprisingly, from 8 to 18 ng/ml in the 200 IU/day group. I say surprisingly as most studies show 200 IU/day does not move 25(OH)D levels significantly, although 25(OH)D levels naturally increase in the third trimester via an unknown mechanism. The authors did not state what season of the year the study was conducted.

After supplementation, 11% of pregnant women in group A (200 IU/day), 40% in group B (50k/month) and 62% of the women in group C (50k/2 weeks) had 25(OH)D above 30 ng/ml.

The highest dose vitamin D group C, reduced insulin resistance compared to the low dose group A. It also caused insulin levels to increase less during the pregnancy. The mean differences of insulin changes and insulin resistance before and after intervention in the low dose versus the high dose were significant (p<.01 and p<.02, respectfully). There were no side effects.

The authors concluded:

“Our study demonstrated that supplementation with 50,000 IU vitamin D every 2 weeks brought about no adverse effects, such as hypercalcemia, in pregnant women. The level of vitamin D for participants of the present study reached more than 30 ng/ml, but remained under the toxic level (more than 100 ng/ml) at the time of delivery. These results are in accordance with Hollis and Wagner, which demonstrated no adverse event due to vitamin D supplementation at a dose of 4,000 IU daily. Our study also demonstrated an appropriate dose of vitamin D supplementation during pregnancy could be 4,000 IU vitamin D daily or 50,000 IU every 2 weeks since this dose of vitamin D was able to raise serum 25-hydroxyvitamin D more than 30 ng/ml decreasing insulin resistance. We recommend 50,000 IU vitamin D every 2 weeks from the 12th week of pregnancy until delivery for pregnant women with vitamin D deficiency.”

However, since only 62% of the pregnant women receiving 50,000 IU every two weeks achieved a 25(OH)D above 30 ng/ml, I would guess the correct dose during pregnancy is probably 50,000 IU/week or about 7,000 IU/day.

  About: John Cannell, MD

Dr. John Cannell is founder of the Vitamin D Council. He has written many peer-reviewed papers on vitamin D and speaks frequently across the United States on the subject. Dr. Cannell holds an M.D. and has served the medical field as a general practitioner, emergency physician, and psychiatrist.