February 19, 2017

Vitamin D in Miscarriage Prevention

May work through immunomodulating pathways
Randomized controlled trial shows vitamin D supplementation reduces pregnancy losses and provides clues to the mechanism of action.


Samimi M, Foroozanfard F, Amini F, et al. Effect of vitamin D supplementation on unexplained recurrent spontaneous abortion: a double-blind randomized control trial. Glob J Health Sci. 2017;9(3):95-102.

Study Objective

To examine the effects of vitamin D supplementation on unexplained recurrent spontaneous abortion (URSA)


Double-blind randomized control trial


The investigators recruited 80 women aged 18 to 35 who were referred to an obstetrical and gynecological hospital-based clinic in Iran for pre-pregnancy care. All of the participants had experienced at least 2 consecutive or 3 nonconsecutive spontaneous abortions of unknown cause, and pregnancy by the same partner in all past and present pregnancies. Participants had no other contributing factors, including uterine abnormalities, thrombophilias, genetic conditions, endocrine disorders, occupational chemical exposures, or sensitivity/allergy to progesterone or vitamin D3.

Study Parameters Assessed

Patients had serum vitamin D and interleukin (IL)-23 levels measured at baseline and again at the completion of the study. Pregnancy loss was considered as spontaneous abortion at any time from the onset of the study to 20 weeks’ gestation.

Primary Outcome Measures

The incidence of spontaneous abortion at any time between the onset of the study and 20 weeks’ gestation was examined, as well as serum levels of IL-23 at onset of pregnancy and again at time of spontaneous abortion or 20 weeks’ gestation.


The intervention group (n=40) received 400 IU per day of vitamin D3 in pill form. The control group (n=40) received an identical placebo without D3. Both groups received 400 mg vaginal progesterone per day. Patients were also given folic acid and iron supplements at least 1 month prior to pregnancy.

Key Findings

Before the start of the study, serum vitamin D levels were 11.65±3.76 ng/mL in the intervention group and 11.53±2.39 ng/mL in the control group (P=0.86). At the completion of the study, levels had changed to 13.21±3.47 ng/mL and 11.08±2.76 ng/mL, respectively (P=0.004). Before the study began IL-23 levels were 20.69±3.01 pg/mL in the intervention group and 21.52±4.37 pg/mL in the control group (P=0.33), and on completion of the study they were 18.4±3.78 pg/mL and 23.16±4.74 pg/mL, respectively (P<0.001). There was an inverse relationship between vitamin D and IL-23 levels (P=0.004). The number of spontaneous abortions during the study period were 5 (12.8%) and 13 (34.2%) in the intervention and control groups, respectively (OR: 3.53; 95% confidence interval [CI]: 1.12-11.2; P=0.03).

When considering confounding factors such as age, gravidity, number of abortions, and IL-23 levels, vitamin D3 levels were not statistically significant (OR: 3.53; 95% CI: 1.12-11.2; P=0.03). However, serum IL-23 levels and incidence of abortion were statistically significant (odds ratio [OR]: 1.63; 95% CI: 1.26-2.11; P<0.001). Based on their analysis, the researchers concluded that vitamin D3 lowers incidence of abortion through the causal pathway with IL-23. They also note that other biological confounders should be considered.

Practice Implications

This study adds to the growing body of research demonstrating the role of vitamin D3 in infertility and recurrent miscarriage. This trial specifically examined the relationship between serum vitamin D3 levels and IL-23 levels and the rate of unexplained recurrent spontaneous abortion (URSA).

A complex disease affecting 2% to 4% of women worldwide, URSA is defined by the American Society of Reproductive Medicine as 2 or more consecutive spontaneous miscarriages prior to 20 weeks’ gestation.1 Advanced maternal age, abnormally low or high body mass index (BMI), alcohol consumption, heavy lifting, and nightshift work have been identified as modifiable risk factors that contribute to miscarriage.2 In the case of URSA, several contributing factors have been recognized, including uterine abnormalities, endocrine disorders, genetic disorders, coagulation disorders, and environmental factors, although the cause for most cases of URSA remains unknown.1

According to the American Pregnancy Association, 40% to 60% of North Americans, including pregnant women, are deficient in vitamin D.

Vitamin D levels have previously been shown to decrease the incidence of first trimester miscarriage; however, no link has been identified between low vitamin D and second trimester miscarriage.3 Women with URSA who have low vitamin D levels are more likely to have antiphospholipid antibodies, antinuclear antibodies, thyroperoxidase antibodies, and increased natural killer (NK) cells than women with normal vitamin D status,4 suggesting an immunomodulating role at the fetomaternal interface. The presence of vitamin D receptors and the enzymes responsible for vitamin D hydroxylation and the identification of localized vitamin D3 synthesis in human placenta and decidua5 further highlight the potential mechanism between vitamin D status and ongoing pregnancy.

Until recently, research on recurrent miscarriage focused on the T-helper type 1 (Th1)/Th2 paradigm. In this paradigm, maternal tolerance to fetal alloantigens is explained by predominant Th2 immunity during pregnancy, which overrules Th1 immunity, thereby protecting the fetus from Th1 cell attack.6 However, more recent evidence points to the Th1/Th2/Th17 and regulatory T cells (Tregs) paradigm.6 There are now several studies indicating an increased Th17/Treg ratio in URSA, creating an inhospitable environment for fetal survival.7 A study by Wang et al found both Th17 and IL-23 were higher in the serum and placenta of women experiencing URSA compared to normal women in early pregnancy.8

Vitamin D3 has been widely studied for its immunomodulating effects, including its ability to suppress cytokine production by Th17. The presence of IL-23, which is secreted by activated type 1 macrophages and dendritic cells, promotes the development of Th17 and resulting cytokines including IL-17. Vitamin D reduces the differentiation of Th17/Treg intermediate cells into Th17 cells, potentially via their high concentration of vitamin D receptors.9 This shift alters the expression of many genes, including the gene for IL-17, therefore potentially reducing the Th17-induced inflammatory pathway associated with URSA.

Several studies focus on serum level of vitamin D3 at the time of miscarriage, but until now none have shown the effects of vitamin D supplementation on pregnancy outcome in URSA. The dosage used in the current study was 400 IU, which is below therapeutic range in almost all regions of the world, with the recommendations from various organizations widely varying from 600 IU to 4,000 IU for pregnant women.10 Of note, the serum levels of vitamin D in both the intervention and control groups were still well below the recommended minimum level of 20 ng/mL at the end of the study, although there was a statistical decrease in IL-23 levels, which the authors attribute to the vitamin D supplementation. The authors do not address the ongoing vitamin D deficiency in the intervention group or indicate if they would expect improved results if serum levels were increased to normal range. Considering the positive outcome of the study with a less than therapeutic dosage of vitamin D3 paired with the already vitamin D-deficient status of the test subjects, one could speculate that using therapeutic levels of vitamin D3 to bring serum levels back into sufficient range may have an even further benefit on the incidence of URSA.

A recent study administered 300,000 IU vitamin D3 by injection in a single bolus dose following Lymphocyte Immune Therapy (LIT), a controversial treatment for URSA. The investigators demonstrated a reduction of the Th17/Treg ratio after vitamin D3 supplementation and showed a promising trend toward better pregnancy outcome in the treatment group. The study was published before all the women who achieved pregnancy had given birth, so data on incidence of miscarriage was not available.11 We can hope to see more studies in this area using therapeutic doses in the near future.

According to the American Pregnancy Association, 40% to 60% of North Americans, including pregnant women, are deficient in vitamin D.12 Considering vitamin D3 is an inexpensive and easily accessible vitamin with a wide range of health benefits including general health, fertility, and pregnancy outcome, it makes much sense to ensure the vitamin D status of patients prior to conception to prevent not only miscarriage, but a wide range of preventable illness and disease.

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  10. Vitamin D Council. Vitamin D during pregnancy and breastfeeding. https://www.vitamindcouncil.org/vitamin-d-during-pregnancy-and-breastfeeding/. Accessed December 19, 2016.
  11. Liang P, Mo M, Li GG, et al. Comprehensive analysis of peripheral blood lymphocytes in 76 women with recurrent miscarriage before and after lymphocyte immunotherapy. Am J Reprod Immunol. 2012;68(2):164-174.
  12. American Pregnancy Association. Vitamin D and Pregnancy. http://americanpregnancy.org/pregnancy-health/vitamin-d-and-pregnancy. Accessed December 20, 2016.