Objective: to assess the effect of vitamin D (VD) supplementation during pregnancy on wheezing or respiratory tract infection in the offspring in the first 5 years of life.
Design: systematic review and meta-analysis of clinical trials and observational studies.
Data sources: the authors conducted a systematic search of PubMed, EMBASE and the Cochrane Library databases. The search was restricted to articles in English.
Study selection: the review included randomised controlled trials (RCTs) that analysed the impact of VD supplementation during pregnancy on the risk of respiratory tract infection and/or wheezing in the offspring. It also included observational studies on the association between serum levels of 25-hydroxyvitamin D during pregnancy or at birth and respiratory tract infection and/or wheezing in the offspring.
Data extraction: two authors reviewed the selected articles. The quality of the studies was assessed by means of the Cochrane Collaboration Risk of Bias Tool in case of RCTs, and the Effective Public Health Practice Projects Quality Assessment Tool in case of observational studies. The authors performed a meta-analysis of the RCTs that provided data on the effects of VD supplementation during pregnancy on offspring wheezing up to age 5 years. The protocol was registered on PROSPERO.
Results: of the 55 eligible articles, four RCTs were selected, one of which showed a significant reduction in the incidence of respiratory tract infections (16%) and medical visits (1.5 visits) with high daily doses of vitamin D (2000 IU) during pregnancy and supplementation with 800 IU/day in infants until age 6 months. The meta-analysis of the other three RCTs showed a decreased risk of wheezing when mothers received vitamin D supplementation during pregnancy (relative risk [RR], 0.81; 95% confidence interval [95 CI], 0.68 to 0.97; P = .025). The observational studies were heterogeneous and generally showed an inverse association between levels of 25-hydroxyvitamin D in pregnant women or umbilical cord blood and the presence of wheezing and/or respiratory disease in the offspring.
Conclusion: supplementation with high-dose vitamin D during pregnancy is associated with a small decrease in the risk of wheezing of the offspring in the first years of life.
Conflicts of interest: the authors disclosed no conflicts of interest.
Funding source: the study was supported by Neomune from the Strategic Research Council, Region of Southern Denmark, University of Southern Denmark, Hans Christian Andersen Children’s Hospital, A.P. Møller Foundation and Arla Foods Ingredients.