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

Background: 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. Objectives: To examine associations between inflammatory biomarkers and VDD with PTB as an outcome. Methods: 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. Results: 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). Conclusions: 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.