Children whose mothers received high-dose vitamin D supplementation while pregnant were not less likely to develop asthma by early childhood, according to new research.

In the initial randomized, double-blind, placebo-controlled VDAART trial, researchers randomly assigned women aged 18 to 39 years who were 10 to 18 weeks pregnant to 4,000 IU of vitamin D daily or placebo. Both study arms also received a daily multivitamin containing 400 IU of vitamin D. All women were nonsmokers and had a history of asthma, eczema or allergic rhinitis or had a partner with a history of asthma, eczema or allergic rhinitis. Asthma, recurrent wheeze or both served as the primary outcome.

Children were originally followed through their third birthday and this study, recently published in The New England Journal of Medicine, extended follow-up through age 6 years. This analysis comprised 806 children.