Pooled estimates from cohort studies have demonstrated no link between antenatal blood vitamin D levels and the presence of asthma/wheeze in later life, according to the results of a systematic review and meta-analysis published in BMC Pulmonary Medicine.

Investigators sought to quantify the effect of early-life vitamin D status on asthma and wheeze in later life. Studies selected from their literature search included randomized controlled trials (RCTs) and cohort studies with vitamin D level in blood (maternal, cord, or infant) or intake (maternal intake during pregnancy or infant intake) and asthma and/or wheeze. Fixed- and random-effects models were used to summarize the risk estimates that compared the highest vs the lowest vitamin D categories.

Of the 1485 studies that were identified, 3 RCTs and 33 cohort studies were included. The 3 RCTs (with a total of 1619 participants) were not included in the meta-analysis because the outcome definitions and comparators were heterogeneous in nature. Overall, 3 RCTs reported a nonstatistically significant effect of vitamin D supplementation during pregnancy on the presence of wheeze or asthma in the offspring at 3 years of age.

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Pooled estimates from cohort studies suggested there was no association between antenatal blood vitamin D levels or vitamin D intake and asthma in offspring, evaluated at either >5 years of age or ≤5 years of age. Moreover, when 2 studies that evaluated the presence of asthma in adulthood were excluded from the review, the estimate for blood vitamin D levels remained unchanged, but a significant inverse association was reported between vitamin D intake and childhood asthma. No association between antenatal vitamin D level and wheeze was revealed.

The investigators concluded that additional trials with sufficient power and longer follow-up time should be conducted to confirm these results of this review. The inconsistent results reported in studies that assessed vitamin D either in blood or intake may be explained by previously reported nonlinear associations between blood vitamin D3 and childhood asthma.

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Shen S-Y, Xiao W-Q, Lu J-H, et al. Early life vitamin D status and asthma and wheeze: a systematic review and meta-analysis. BMC Pulm Med. 2018;18(1):120.