Allergic diseases have seen a rise worldwide, with children suffering the highest burden. Thus, early prevention of allergic diseases is a public health priority.

To synthesize the evidence from randomized controlled trials (RCTs) assessing the effect of vitamin interventions during pregnancy on developing allergic diseases in offspring.

We searched CENTRAL, MEDLINE, SCOPUS, World Health Organization's International Clinical Trials Registration, E-theses, and Web of Science. Study quality was evaluated using Cochrane's risk of bias tool. Included RCTs had a minimum of 1-month follow-up postgestation.

A total of 5 RCTs met the inclusion criteria, including 2456 children who used vitamins C + E (1 study), vitamin C (1 study), and vitamin D (3 studies) compared with placebo/control. Two studies were judged to have a high risk of bias for performance bias or a 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 vitamin C + E studies due to high heterogeneity between the 2 included studies. However, we did conduct a meta-analysis with trials on vitamin D (including 1493 children) and the results showed an association between the prenatal intake of vitamin D and the risk of developing recurrent wheeze in offspring (relative risk (RR), 0.812; 95% CI, 0.67-0.98).

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 is needed to ascertain whether this observed effect is sustained. There is lack of evidence on the effect of other vitamins for the prevention of respiratory and/or allergic outcomes.