Published online: March 9, 2017
Nutrient trials are different from drug trials, primarily because participants may have different levels of intake of the nutrient and thus have varying baseline nutrient status prior to entry into a trial. Additionally, the intervention dose needs to be sufficient to produce a change in the nutrient status, which depends on the initial status at entry into the trial. These issues may have affected the results of recent asthma prevention trials with vitamin D, where pregnant women were randomized to vitamin D supplementation or placebo, without regard for initial vitamin D status on entry into the trials.
The Vitamin D Antenatal Asthma Reduction Trial (VDAART) is a randomized, double-blind, placebo-controlled trial of pregnant women at risk of having children with asthma randomized to a total daily dose of 4,400 IU (4,000 IU/day vitamin D plus a prenatal vitamin containing 400 IU vitamin D) or a total daily dose of 400 IU (placebo plus 400 IU/day vitamin D). The investigators measured circulating vitamin D levels (25hydroxyvitamin D or 25(OH)D) in the mothers, then followed the children after birth to see who developed either asthma or recurrent wheeze by 3 years of age. While this study showed a 20% relative reduction in the risk for the main study outcome of asthma and/or recurrent wheeze (asthma/recurrent wheeze) in the 3-year old children born to the mothers randomized to the vitamin D arm, the result did not meet strict statistical significance (p=0.051).
In a recent study published in The Journal of Allergy and Clinical Immunlolgy (JACI), Wolsk and colleagues undertook secondary analyses of the VDAART trial data to investigate whether treatment had differential effects by race, whether the initial and achieved prenatal levels of 25(OH)D were associated with the outcome of asthma/recurrent wheeze in the offspring at age 3 years, and whether the maternal levels modified the effect of vitamin D supplementation.
The authors did not find differences between African American and non-African American mothers in the effect of maternal vitamin D supplementation and asthma/recurrent wheeze in the offspring at age 3 years. Both initial and achieved 25(OH)D levels in the mothers during pregnancy were inversely associated with asthma or recurrent wheeze in the 3-year old children. Supplementation with daily 4,400 IU vitamin D in pregnancy, particularly in those mothers with higher levels of vitamin D in early pregnancy (a level of at least 30 ng/ml) was found to reduce the risk of asthma/recurrent wheeze in the offspring through age 3 by about 58%.
These findings are of great public health interest because vitamin D deficiency is particularly prevalent in pregnancy. Findings from this study will need to be confirmed in other studies, but they suggest that measurement of vitamin D levels and supplementation with vitamin D in pregnancy may help in preventing asthma and wheezing illnesses in early childhood.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.