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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 case-control study finds vitamin D deficiency associated with increased risk of preterm birth

A new study out of Pittsburgh has found that vitamin D deficiency may increase risk of preterm birth among black and Puerto Rican mothers.

Preterm birth is characterized by any baby born before 35 weeks of gestation (full term is 39 weeks). Preterm birth is a growing issue worldwide. One in every 8 babies born are born prematurely. In 2010 alone, more than 1 million premature babies died worldwide, making preterm birth the second leading cause of death in children under 5 years old.

Premature babies are susceptible to problems including apnea, jaundice, anemia, and bleeding in the brain. On top of that, preterm birth is a major cause of long-term neurological disabilities.

Risk factors for mothers include smoking, poor nutrition, being underweight or overweight before pregnancy, stress, physical injury, and conception through in vitro fertilization.

In recent years, researchers have looked at whether vitamin D plays a role in pregnancy complications, including preterm birth.

One of the causes of preterm birth is bacterial vaginosis. Bacterial vaginosis is caused by bacterial colonization of the placenta. Vitamin D has been shown to reduce the risk of bacterial infections. Additionally, vitamin D is known to help regulate immunity and inflammation which is important during pregnancy. So might vitamin D help prevent preterm birth?

In the current study, Dr. Lisa Bodnar and her team at University of Pittsburgh wanted to see the relationship between maternal vitamin D deficiency at or before 26 weeks’ gestation and risk of spontaneous preterm birth (sPTB).

They used data from the Collaborative Perinatal Project (CPP). The CPP was a large cohort study involving nearly 42,000 women from 1959 – 1965. This researchers established a subcohort to study preterm birth specifically. After much augmentation and random selection, the researchers eventually had a sample including 2,629 pregnancies in the subcohort and 839 cases of preterm birth. Of the 839 cases, 767, or 91% were sPTBs.

The researchers conducted placental histology to determine vascular and inflammatory lesions, both indicators of preterm birth and fetal growth restrictions. Maternal serum was frozen at the time of the original study and then analyzed for vitamin D levels for the current study.

Here’s what the researchers found:

  • The mean maternal vitamin D levels were 17.2 ng/mL and 84% of the women had vitamin D levels less than 30 ng/mL.
  • Among nonwhite mothers, the incidence of sPTB decreased significantly as vitamin D levels increased. The same was not true for white mothers, although there were only 29 in the study.
  • After adjusting for things like maternal race, age and socioeconomic status, vitamin D levels greater than 12 ng/mL were associated with a 20-30% reduced risk of sPTB compared with levels lower than 12 ng/mL.

The researchers concluded,

“Vitamin D may have relevance to the prevention of particular subtypes of sPTB, but more work is needed to rigorously evaluate this association with large contemporary cohorts of mothers from a wide range of racial and ethnic backgrounds with detailed data on skin pigment and other covariates.”


Bodnar, LM et. al. Maternal Vitamin D Status and Spontaneous Preterm Birth by Placental Histology in the US Collaborative Perinatal Project. American Journal of Epidemiology, 2013.


  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.