Abstract
INTRODUCTION: Poor respiratory health in childhood is common, and asthma is the most common chronic disease among children, for which there is no known cure. Maternal intake of vitamins (A, C, E) may be a modifiable nutritional exposure to reduce adverse respiratory health in offspring. OBJECTIVE: We aimed to systematically review the evidence for the association between maternal vitamin (A, C, E) intake during pregnancy (via questionnaire or blood assay) and respiratory outcomes in the offspring. METHODS: Studies identified through electronic databases were eligible if they assessed maternal levels and/or intake of vitamins A, C and/or E via dietary intake or supplements in pregnancy and respiratory outcomes in the first 5 years of life. Meta-analyses were conducted where possible. Outcomes included wheeze, cough, asthma, infant respiratory distress syndrome (RDS), respiratory tract infection (RTI) and lung function measurement. RESULTS: Of 1170 articles screened, 12 observational studies and six RCTs met the inclusion criteria (total sample size n = 58,769). Meta-analysis could not be performed for vitamin A; however, there was no evidence to suggest that maternal vitamin A intake improves early life respiratory outcomes in offspring. Two RCTs found that vitamin C supplementation (500 mg/day vs. placebo) reduced the incidence of wheeze at 12 months (n = 206 children) and 5 years (n = 213 children) in pregnancies exposed to smoking. In meta-analyses, maternal intake in the highest vitamin E quartile versus lowest reduced the odds of wheeze at 2 years by 36% (aOR: 0.64, 95% CI: 0.47-0.87, n = 2 observational studies, very low certainty); this was not true for vitamin C intake (aOR: 0.85, 95% CI: 0.63-1.16, n = 2 observational studies, very low certainty). Vitamin supplementation (C + E) was not associated with infant RDS (OR: 1.15, 95% CI: 0.80-1.64, n = 2 studies, moderate certainty) relative to placebo. CONCLUSION: There may be some benefit to vitamin C supplementation during pregnancy in the context of maternal smoking or higher maternal vitamin E intake during pregnancy, for reducing the risk of childhood wheeze in early life. This emerging evidence warrants further studies to enable translation into dietary guidelines.