Vitamin D Deficiency and IL-6: Risk Factors for Preterm Birth in Black Women: A Retrospective Cross-Sectional Study

Non-Hispanic Black women have a 1.5 times greater rate of preterm birth (PTB, any birth occurring at <37 wk of gestation) than non-Hispanic White women. Black women are also more likely to have vitamin D deficiency (VDD; 25[OH]D <20 ng/mL) than White women. Vitamin D has anti-inflammatory effects, which may help explain the association of VDD with PTB in Black women.

To examine associations between inflammatory biomarkers and VDD with PTB as an outcome.

We used an exploratory retrospective cross-sectional design utilizing data collected as part of the larger Biosocial Impact on Black Births (BIBB) study. A case-control subsample was selected from the BIBB participants who had stored blood plasma available at 8-25 wk of gestation (n = 172). Fifty-nine PTB cases were included in the current study, with a set of matched controls based on maternal age controls at a 1:2 ratio of PTB to term birth (n = 113, 65.6%). Total 25(OH)D and cytokine levels were measured in the plasma.

Seventy percent of women with PTB had VDD compared with 50% of women with term birth who had VDD. Other inflammatory biomarkers were not associated with PTB except for IL-6. The PTB group had higher IL-6 and lower 25(OH)D levels compared with term birth. In adjusted models controlling for IL-6 and other covariates, odds ratios (OR) for VDD remained significant for predicting PTB (OR: 2.45; 95% confidence interval: 1.18, 5.06; P = 0.016).

Increased VDD was associated with increased risk of PTB among Black women after controlling for IL-6 and other factors. Achieving adequate vitamin D status in early pregnancy may have an important role in PTB prevention as it is a significant predictor of risk after inflammation and other factors are considered. Further investigation is warranted.