Environmental Factors May Explain Some Racial Differences in Childbirth

Environment and PregnancyAlthough one theory explaining the differences in birth outcomes among black and white women in the United States is a difference in vitamin D levels, a new study investigating racial disparities in birth outcomes as published in the American Journal of Epidemiology suggests that environmental factors other than vitamin D account for the differences in preterm birth and low birth weight among the two groups.

Explains Zaneta Thayer, PhD, assistant professor of anthropology at the University of Colorado Denver:

“For years there has been this hypothesis that African-Americans have worse birth outcomes because they have more melanin in their skin which reflects the sun and therefore lowers levels of Vitamin D. But in examining the relationship between ultraviolet exposure and birth outcomes nationwide, there was no evidence to support this.”

The theory that vitamin D levels account for the difference in preterm birth and low birth weight among black and white mothers stems from the ability to synthesize vitamin D from ultraviolet light. Individuals with darker skin have high concentrations of melanin and are subsequently less able to absorb vitamin D from the sun. Thus, some researchers have hypothesized that the higher rates of negative birth outcomes among black women is a result of a lowered ability to synthesize vitamin D from the sun.

Vitamin D, or the sunshine vitamin, is a essential nutrient primarily responsible for enhancing intestinal absorption of calcium and phosphate. The vitamin is available through food sources and supplements but is also synthesized by the body after adequate exposure to sunlight. Pregnancy is a known risk factor for vitamin D deficiency. Inadequate levels of vitamin D increases the risk of pregnancy complications, bone disorders, cardiovascular disease, diabetes, and some cancers.

However, differences in socioeconomic status and racial discrimination have also been linked to difference in birth outcomes among pregnant women as well as other health problems.

For the present study, the researchers collected data on UV exposure in 48 states or territories using information compiled from the National Oceanic and Atmospheric Administration (NOAA) National Weather Service website as well as data on birth outcomes, specifically low birth weight and preterm births, from the National Centers for Disease Control and Prevention.

According to the study, states with the highest income inequalities had higher differences in birth outcomes across the UV spectrum. Racial differences in low birth weight and preterm births were also highest among women living in areas with high UV exposure and greater income inequality.

In other words, socioeconomic differences appear to have a greater effect on the difference in birth outcomes among black and white women than differences in vitamin D levels.

Comments Thayer, “Given the UV hypothesis, we would expect that women who live in the South would have better birth outcomes than those living in the North. However, the present analysis suggests the exact opposite, with both absolute rates as well as racial disparities in adverse birth outcomes being greatest in southern states.”

North Dakota and Vermont, which had the second and third lowest UV Indexes respectively, had the lowest racial disparities in preterm births and low birth weights.

Adds Thayer, “The results suggest that the environment is a stronger contributor to adverse birth outcomes than genes, since there are differences in rates of birth outcomes across states. That said, it seems unlikely that disparities in birth outcomes in the U.S. are primarily shaped by differences in UV induced vitamin D status.”

The results of the present study indicate that problems like poverty and discrimination that commonly occur along racial lines should be addressed to help improve birth outcomes among all women.


Environmental Factors May Explain Some Racial Disparities in Childbirth:
Sociodemographic and Community Factors Contributing to Preterm Birth:

Image Credits

Environment and Pregnancy:

Cycling Vigorously

Vigorous Exercise May Reduce Flu Risk

Fried Eggs in Pan

Link Between Saturated Fat and Heart Disease Questioned