In utero exposure to 25(OH) D and risk of childhood asthma, wheeze and respiratory tract infections: Ameta-analysis of birth cohort studies

Background Studies of the associations between in utero 25-hydroxyvitamin D [25(OH) D] exposure and childhood asthma risk, wheeze and respiratory tract infections are inconsistent and inconclusive. Objectives To assess the associations between 25(OH) D levels in cord blood or maternal venous blood and risk of offspring’s asthma, wheeze and respiratory tract infections. Methods Data were derived from PubMed, EMBASE, Google Scholar, references from relevant articles, and de novo results from published studies until December, 2015. Random-effects meta-analysis was conducted among 16 birth cohort studies. Results Comparing the highest to the lowest category of 25 (OH) D levels, the pooled ORs were 0.84 (95% CI, 0.70 to 1.01; P = 0.064) for asthma, 0.77 (0.58 to 1.03; P = 0.083) for wheeze, and 0.85 (0.66 to 1.09; P = 0.187) for respiratory tract infections. The observed inverse association for wheeze was more pronounced and became statistically significant in the studies that measured 25 (OH) D levels in cord blood (0.43, 0.29 to 0.62; P < 0.001). Conclusions Accumulated evidence generated from this meta-analysis suggests that increased in utero exposure to 25 (OH) D is inversely associated with the risk of asthma and wheeze during childhood. These findings are in keeping with the results of two recently published randomized clinical trials of vitamin D supplementation during pregnancy.