Prenatal intake of vitamins and allergic outcomes in the offspring: a systematic review and meta-analysis

Background - Allergic diseases have seen a rise worldwide with children suffering the highest burden. Thus early prevention of allergic diseases is a public health priority. Objective - To synthesise the evidence from randomised controlled trials (RCTs) assessing the efficacy of vitamin interventions during pregnancy on developing allergic diseases in offspring. Methods - We searched CENTRAL, MEDLINE, SCOPUS, WHO’s Int. Clin. Trials Reg., E-theses and Web of Science. Study quality was evaluated using the Cochrane’s risk of bias tool. Included RCTs had a minimum of 1-month follow-up post gestation.Results - A total of five RCTs met the inclusion criteria, including 2456 children that used vitamins C+E (one study), vitamin C (one study) and vitamin D (three studies) compared with placebo/control. Two studies were judged to have a high risk of bias for performance bias or high rate of loss to follow-up. All were rated as low risk of bias for blinding of outcome assessment. We did not perform meta-analysis with vitamin C or C+E studies due to high heterogeneity between the two included studies. However we did conduct a meta-analysis with trials on vitamin D (including 1493 children) and the results showed an association between prenatal intake of vitamin D and the risk of developing recurrent wheeze in offspring (RR=0.812, 95 % CI=0.67-0.98). Conclusion - The current evidence suggests that prenatal supplementation of vitamin D, might have a beneficial effect on recurrent wheezing in children. Longer-term follow-up of these studies are needed to ascertain whether this observed effect is a sustained. There is lack of evidence on the effect of other vitamins for prevention of respiratory and/or allergic outcomes.