Vitamin D supplementation in pregnancy, prenatal 25(OH)D levels, race, and subsequent asthma or recurrent wheeze in offspring: Secondary analyses from the Vitamin D Antenatal Asthma Reduction Trial

Background Nutrient trials differ from drug trials because participants have varying circulating levels at entry into the trial. Objective We sought to study the effect of a vitamin D intervention in pregnancy between subjects of different races and the association between 25-hydroxyvitamin D₃ (25[OH]D) levels in pregnancy and the risk of asthma/recurrent wheeze in offspring. Methods The Vitamin D Antenatal Asthma Reduction Trial is a randomized trial of pregnant women at risk of having children with asthma randomized to 4400 international units/d vitamin D or placebo plus 400 international units/d vitamin D. Asthma and recurrent wheezing until age 3 years were recorded. Results African American (AA) women (n = 312) had lower initial levels of 25(OH)D (mean [SD], 17.6 ng/mL [8.3 ng/mL]) compared with non-AA women (n = 400; 27.1 ng/mL [9.7 ng/mL], P <.001). No racial difference was found from vitamin D supplementation in pregnancy on asthma/recurrent wheezing in offspring (P for interaction =.77). Having an initial level of greater than 30 ng/mL and being randomized to the intervention group was associated with the lowest risk for asthma/recurrent wheeze by age 3 years compared with having an initial level of less than 20 ng/mL and receiving placebo (adjusted odds ratio, 0.42; 95% CI, 0.19-0.91). Conclusions We did not find differences between AA and non-AA mothers in the effect of maternal vitamin D supplementation and asthma/recurrent wheeze in offspring at 3 years. Maternal supplementation of vitamin D, particularly in mothers with initial 25(OH)D levels of greater than 30 ng/mL, reduced asthma/recurrent wheeze in the offspring through age 3 years, suggesting that higher vitamin D status beginning in early pregnancy is necessary for asthma/recurrent wheeze prevention in early life.