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New study finds vitamin D levels of at least 40 ng/ml reduce risk of preterm birth

Posted on: August 2, 2017   by  Amber Tovey


A new study, using the data from our friends at GrassrootsHealth, found vitamin D levels above 40 ng/ml were associated with significantly reduced risk of preterm birth.

Approximately 15 million infants are born prematurely (< 37 weeks gestation) and more than one million infant deaths result from complications of preterm birth each year. In the United States, an estimated 12% of women give birth to preterm babies.

Maintaining sufficient vitamin D levels throughout pregnancy is an essential component for a healthy pregnancy. The clinical trial that best illustrates this was conducted by Professors Bruce Hollis and Carole Wagner. The study found that 4,000 IU of vitamin D daily led to fewer pregnancy complications than 2,000 IU daily. Furthermore, the study discovered that lower pre-delivery 25(OH)D was significantly predictive of preterm delivery.

Despite the well-established role of vitamin D during pregnancy, the average prenatal vitamin only contains 400 IU of vitamin D. In addition, skeptics still question the need for vitamin D levels above 20 ng/ml.

In a recent study, researchers aimed to determine the relationship between vitamin D levels and preterm birth at an urban medical center treating a large, diverse population. The researchers analyzed data from 1,064 women. Preterm births occurred in 13% of the women. The data revealed that women with vitamin D levels of 40 ng/ml or higher had a 62% lower risk of preterm birth compared to women with vitamin D levels below 20 ng/ml (p < 0.0001). After adjusting for socioeconomic variables, this relationship remained, with levels of 40 ng/ml or higher associated with a 59% reduced risk of preterm birth.

The researchers also wanted to know whether vitamin D may only play a role in a specific type of preterm birth. Preterm births are commonly divided into two categories, spontaneous and indicated. About a quarter of preterm births are indicated, meaning that the medical team decided to induce labor early, often due to eclampsia or other serious medical conditions. The rest of preterm births are known as spontaneous preterm births, which happens when one goes into labor prematurely or her cervix opens prematurely. The study found that vitamin D levels of 40 ng/ml or higher were associated with similar reductions of spontaneous and indicated preterm births, with 58% and 68% reduced risk, respectively (p = 0.02, 0.06).

The findings from this study supports the Vitamin D Council’s recommended vitamin D status of 40-60 ng/ml for optimal health.

The researchers concluded,

“Vitamin D testing and supplementation of pregnant women is a safe, affordable prevention tool that could substantially reduce the occurrence of [preterm birth] and the heavy burden of associated morbidity, mortality and economic costs.”

They also stated,

“These findings…highlight the importance of achieving a [vitamin D] concentration substantially above 20 ng/ml, the concentration recommended by the IOM for pregnant women, for preterm birth prevention.”


Tovey, A. & Cannell, JJ. New study finds vitamin D levels of at least 40 ng/ml reduce risk of preterm birth. The Vitamin D Council Blog & Newsletter, July 28, 2017.


McDonnell, S. Baggerly, K. Baggerly, C. & et al. Maternal 25(OH)D concentrations >40 ng/mL associated with 60% lower preterm birth risk among general obstetrical patients at an urban medical center. PLOS One, 2017.

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