Adequate gestational vitamin D may protect against tobacco smoke effects on child lung function

Published: November 15, 2022

With over 1 billion tobacco smokers, approximately 40% of children are exposed to tobacco smoke globally. Tobacco smoke exposure (TSE) has been related to harmful health outcomes in children, such as preterm birth, asthma development, and reduced lung function. Vitamin D plays a role in fetal lung and immune system development, and insufficient vitamin D level during pregnancy has been associated with reduced childhood lung function. Prior studies suggest that vitamin D may modify the effects of environmental exposures, however, none have investigated gestational vitamin D and TSE throughout pregnancy and early life.

In a recent original article published in The Journal of Allergy and Clinical Immunology (JACI), Knihtilä and colleagues examined the effects of early life TSE on child lung function, and the effects of gestational vitamin D status on this association in the Vitamin D Antenatal Asthma Reduction Trial (VDAART). VDAART is a prospective, multi-center study that randomized non-smoking pregnant US women to high-dose vitamin D supplementation or placebo. The authors used cotinine, the predominant nicotine metabolite, as an objective measure of TSE to avoid potential biases related to self-reported TSE. Plasma cotinine levels were measured in the mothers during pregnancy (at 10-18 and 32-38 gestational weeks) and children during early life (1, 3, and 6 years) to calculate a time- and dose-dependent estimate for cumulative TSE. Child lung function was assessed at age 6 years with 2 different methods: spirometry and impulse oscillometry. Gestational vitamin D level was measured in the mothers at recruitment (10-18 gestational weeks) and at third trimester (32-38 gestational weeks).

A total of 476 mother-child pairs were included in the study. Of the study subjects, 205 (43%) had at least one increased cotinine level suggesting TSE during follow up. Given that only women who were self-reported nonsmokers at enrollment were included in the VDAART, most of the reported TSE during follow up was secondhand. Cumulative TSE from pregnancy to childhood was associated with dose- and duration-dependent decreases in child lung function at age 6 years as measured by both spirometry and impulse oscillometry. Subjects in the highest cumulative TSE group were found to have a 16% lower lung function as measured by spirometry (FEV1) than their peers without increased cotinine levels during follow-up. In total 189 (40%) study subjects had insufficient (<30 ng/ml) gestational vitamin D levels at both time points during pregnancy. Significant associations demonstrating decreasing lung function with increasing cumulative TSE were observed among subjects with insufficient vitamin D levels throughout pregnancy, whereas no association between TSE and child lung function was observed among those with sufficient vitamin D levels, suggesting that maintaining an adequate vitamin D level throughout pregnancy may protect against the effects of TSE on offspring lung function.

This study indicates that early life TSE is associated with dose- and duration-dependent decreases in child lung function even in the absence of reported maternal smoking. Gestational vitamin D status appears to contribute to resilience against TSE and have therapeutic potential for minimizing the adverse effect of TSE on offspring lung function.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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