Vitamin D supplementation in primary allergy prevention: Systematic review of randomized and non-randomized studies

Background To date, a systematic review of the evidence regarding the association between vitamin D and allergic diseases development has not yet been undertaken. Objective To review the efficacy and safety of vitamin D supplementation when compared to no supplementation in pregnant women, breastfeeding women, infants, and children for the prevention of allergies. Methods Three databases were searched through January 30, 2016, including randomized (RCT) and nonrandomized studies (NRS). Two reviewers independently extracted data and assessed the certainty in the body of evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. Results Among the 1932 articles identified, one RCT and four NRS were eligible. Very low certainty in the body of evidence across examined studies suggests that vitamin D supplementation for pregnant women, breastfeeding women, and infants may not decrease the risk of developing allergic diseases such as atopic dermatitis (in pregnant women), allergic rhinitis (in pregnant women and infants), asthma and/or wheezing (in pregnant women, breastfeeding women, and infants), or food allergies (in pregnant women). We found no studies of primary prevention of allergic diseases in children. Conclusion Limited information is available addressing primary prevention of allergic diseases after vitamin D supplementation, and its potential impact remains uncertain.