Vitamin D Supplementation During Pregnancy Reduced Rates of Asthma, Wheezing in Children

Research published in the Journal of Allergy and Clinical Immunology found that vitamin D supplementation during pregnancy had reduced the rates of asthma and wheezing in children, compared to a standard prenatal multivitamin. Vitamin D, which is a nutrient that comes from sunlight exposure, diet, or supplements, is considered essential to bone health but has other roles in autoimmune conditions and illnesses.

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"Vitamin D deficiency is very common, especially in pregnant women who are not taking supplements," said first study author Scott T. Weiss, MD, MS, associate director of the Channing Division of Network Medicine at Brigham Women's Hospital and professor at Harvard Medical School, in a press release. “Based on our findings, we would recommend that all pregnant women consider a daily intake of at least 4400 IU vitamin D3 throughout their pregnancy, starting at the time of conception.”

The authors of the review observed a link with vitamin D deficiency to childhood asthma and wheezing, which is a common cause of illness in young children. In addition, approximately 40% of children report experiencing daily wheezing at age 3 years, and by age 6 years, 20% are diagnosed with asthma, according to the press release. Prior research suggested that higher vitamin D levels during pregnancy can be protective against asthma; however, a clinical study—the Vitamin D Antenatal Asthma Reduction Trial (VDAART)—was inconclusive when comparing the vitamin D supplement group with the non-supplement group.

According to Weiss, understanding the role of a nutrient during pregnancy requires consideration of the nutrient dose, the timing of starting the dose, and the baseline levels in the control group. The original VDAART trial as well as other meta-analyses of vitamin D supplementation during pregnancy did not take this into consideration. The original VDAART trial examined pregnant women between 10 and 18 weeks of pregnancy with a family history of allergies or asthma. Half of the enrolled participants received a dose of 4400 IU of vitamin D in addition to the 400 IU in their prenatal vitamin, whereas the other half received placebos alongside their prenatal vitamin.

"In general, the observational studies show an effect, but the clinical trials don't because nutrient trials are very different from drug trials. In a drug trial, you're comparing giving a drug to giving no drug. In a nutrient trial, you're comparing more of a nutrient to less, but that baseline amount in the control group is variable,” said Weiss in the press release. “But, when we stratified the results by the vitamin D level in the control group, both of those analyses became significant. When you adjust for baseline vitamin D levels, we see exactly the effect in the observational studies—a 50% reduction in asthma and wheezing."

A review article in the American Journal of Clinical Nutrition summarized the studies as well as genetic findings that further emphasize the possibility of a relationship between vitamin D and asthma. Additional research is needed to further evaluate the association between vitamin D and asthma.

“Based on the insights gained from VDAART, we recommend that a follow-up clinical trial should start as early as possible in pregnancy and supplement with 6000 IU vitamin D and seek a very high enrollment of women of color,” said Weiss in the press release. “Such trials could deepen our understanding of the potential impact of vitamin D on pregnancy outcomes and early-life asthma.”

Reference

Brigham and Women’s Hospital. Clinical trial data suggests prenatal vitamin D reduces a child’s risk of asthma. News release. November 9, 2023. Accessed November 9, 2023. https://www.eurekalert.org/news-releases/1007534