Lower levels of vitamin D may be linked with a higher rate of preterm births among black and Puerto Rican women, according to a new University of Pittsburgh study.
Funded by the National Institutes of Health and published in the online version of the American Journal of Epidemiology, the study is the largest ever looking at the link between preterm births and vitamin D.
Researchers found that spontaneous preterm births among non-white mothers dropped by 30 percent when vitamin D levels increased.
No such link between preterm births and vitamin D was found in white women. Preterm is defined as less than 37 weeks of gestation.
But Lisa Bodnar, the lead author of the study, cautioned that it was observational -- comparing data and blood samples from a large, geographically diverse study of thousands of women done in the 1960s in a dozen medical centers across the country. While they found the drop in preterm births intriguing, they still aren't sure vitamin D is the reason.
"There may be other factors involved," said Ms. Bodnar, adding that data is continuing to be collected at Magee-Womens Hospital of UPMC for future studies.
The Pitt researchers looked at 30,000 women from the Collaborative Perinatal Project, which ran from 1959 to 1965 -- and found that of the 767 preterm births recorded, 66 percent of the mothers were black, 28 percent were white and 6 percent were Puerto Rican.
"The women who delivered preterm had all the risk factors -- they were from low socio-economic backgrounds, they were black, they were smokers," she said. When they looked at black women with sufficient levels of vitamin D, they were far less likely to go into early labor and give birth.
"Still, we don't know for sure based on a study like this," Ms. Bodnar said. "Maybe there's something out there we didn't measure, like a healthier lifestyle, or depression or more time outdoors in the sunshine," which is a major source of vitamin D in late spring, summer and early fall in Pittsburgh.
"I wouldn't recommend screening and treatment based on this data, but it does justify further research," added Hyagriv N. Simhan, the study's senior author and chief of maternal fetal medicine and medical director of obstetrics services at Magee. "Previous to this work there were hints of a link, but this study merits enthusiasm because of its size and methodology."
More than half of all black women and about 5 percent of white women have vitamin D levels that are too low, previous research has found.
While the nation's rate of preterm births has dropped slightly since 2006, according to the U.S. Centers for Disease Control and Prevention, the problem of preterm births continues to confound modern obstetricians because so many of these babies die.
In 2010, the study's researchers noted, 1 million infants born preterm died worldwide, making it the second-leading cause of death in children under age 5.
Those who survive are at increased risk of chronic lung disease, deafness, blindness and learning and cognitive disabilities.
The problem is particularly acute in the Pittsburgh metropolitan area.
In 2010, the infant mortality rate -- those who die within the first year of life -- was 7.2 per 1,000 births, or 17 percent higher than the national rate of 6.15 percent. Among black women in the Pittsburgh area, it was 25 percent higher than the national rate and behind that of many developing nations.
Mackenzie Carpenter: firstname.lastname@example.org; 412-263-1949. On Twitter @mackenziePG.
Mackenzie Carpenter: email@example.com or 412-263-1949. First Published October 30, 2013 1:05 PM