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"It is especially important to understand how vitamin D influences preterm birth among black mothers," says Lisa Bodnar. "Vitamin D supplementation could be an easy way to reduce the high rates of preterm birth in this group." (Credit: iStockphoto)

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Low vitamin D raises risk of preterm birth for black moms

African-American and Puerto Rican women who have low levels of vitamin D during pregnancy are more likely to go into labor early and give birth to preterm babies, research shows.

“Vitamin D is unique in that while we get it from our diets, our primary source is our body making it from sunlight,” says Lisa Bodnar, associate professor in the department of epidemiology at the University of Pittsburgh.


“Previous studies using conservative definitions for vitamin D deficiency have found that nearly half of black women and about 5 percent of white women in the United States have vitamin D concentrations that are too low.”

Among non-white mothers, the incidence of spontaneous, preterm birth—naturally going into labor two or more weeks before the 37 weeks of pregnancy considered full-term—decreased by as much as 30 percent as vitamin D levels in the blood increased.

The researchers did not find a similar relationship between maternal vitamin D levels and preterm birth in white women.

“We were concerned that finding this association only in non-white women meant that other factors we did not measure accounted for the link between low vitamin D levels and spontaneous preterm birth in black and Puerto Rican mothers,” Bodnar says.

She and colleagues used methods to account for the expected influence of discrimination and socioeconomic position, as well as fish intake and physical activity. “Even after applying these methods, vitamin D deficiency remained associated with spontaneous preterm birth.”

1 million infants

“Preterm birth is the most important problem in modern obstetrics,” says senior author chief of the division of maternal-fetal medicine and medical director of obstetrical services at Magee-Womens Hospital.

“In 2010, over 1 million infants born preterm at less than 37 weeks gestation died worldwide. Preterm infants who survive are at risk of chronic lung disease, deafness, blindness, or other visual impairment, and learning and cognitive disability.”

A novel part of the study was the availability of information from placental examinations. The researchers found that vitamin D deficiency was most strongly related to preterm births with damage to the placenta caused by inflammation.

“This finding may give us insight into the biology connecting low vitamin D and preterm birth,” Simhan says. “It holds great promise and will motivate significant preterm birth research.”

For the study, published online in the American Journal of Epidemiology, researchers used a sample of over 700 cases of preterm birth and 2,600 full-term births collected by the Collaborative Perinatal Project, which was conducted in 12 US medical centers from 1959 to 1965. The blood samples collected by the project were well-preserved and able to be tested for vitamin D levels 40 years later.

“It is critical to repeat this study in a modern sample,” says Bodnar, noting that pregnant women today smoke less, have less sun-exposure, and receive more vitamin D in their foods than the mid-century cohort.

“Further, it is especially important to understand how vitamin D influences preterm birth among black mothers. Vitamin D supplementation could be an easy way to reduce the high rates of preterm birth in this group.”

Researchers from McGill University and Ohio State University contributed to the study, which was supported by the National Institutes of Health.

Source: University of Pittsburgh

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