The study, “Six-Year Follow-up of a Trial of Antenatal Vitamin D for Asthma Reduction,” was published in the New England Journal of Medicine and is a continuation of previous research — completed in 2016 — that suggested that prenatal vitamin D supplementation provided a protective effect on asthma in children up to age three. The study aimed to determine whether, when maternal levels of 25-hydroxyvitamin D were taken into account, children born to mothers who had received 4400 IU of vitamin D3 per day during pregnancy (vitamin D group) would have a lower incidence of asthma and recurrent wheeze at the age of six years than would those born to mothers who had received 400 IU of vitamin D3 per day.
“The hypothesis was that vitamin D could affect uterine programming and immune development,” said Litonjua, chief of the Division of Pulmonary Medicine in the Department of Pediatrics at UR Medicine’s Golisano Children’s Hospital. “We wanted to study the effects on children for several years because asthma is very difficult to diagnose early in life.”
Vitamin D — which is typically boosted by greater exposure to sunlight — has emerged as a possible treatment option due to the prevalence of asthma and allergies in the Northern Hemisphere. Vitamin D supplementation during pregnancy may also reduce the risk of pre-eclampsia, low birthweight and preterm birth. The evidence currently available, however, to directly assess the benefits and harms of the use of vitamin D supplementation alone in pregnancy for improving maternal and infant health outcomes is limited.
The results of Litonjua’s study showed that the protective effects of antenatal vitamin D on asthma-like symptoms diminished each subsequent year of the child’s life from birth. Of note, the study design did not include vitamin D supplementation after birth, and the differences in vitamin D levels equalized in both the control and experimental group from one through six years. While this study indicates that prenatal vitamin D supplementation alone has limited effect on preventing asthma and wheezing in children, a more definitive study design would be to supplement during both the prenatal and postnatal periods.
“Once you start inflammation with asthma it keeps going,” Litonjua said. “Vitamin D tends to stop it, so we would want to study the early effects by providing supplementation during early childhood.”
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