Vitamin D supplementation attenuates asthma development following traffic-related particulate matter exposure.

Background: Recent literature suggests that children who are vitamin D deficient are uniquely susceptible to the effects of traffic-related air pollution (TRAP) exposure. This is highly significant because large segments of the population reside in zones of high TRAP exposure.

Objective: We sought to determine whether vitamin D supplementation mitigates the effect of TRAP exposure on asthma development, asthma exacerbation, and/or airway inflammation and to determine the timing of vitamin D supplementation that confers maximal health benefit.

Methods: Using established mouse models of asthma, we examined the effect of prenatal and postnatal vitamin D supplementation on asthma development, as well as the utility of vitamin D as a treatment for established asthma in the context of diesel exhaust particle (DEP) exposure.

Results: DEP and allergen coexposure resulted in increased airway hyperresponsiveness (AHR) and accumulation of pathogenic TH2/TH17 cells in the lungs of vitamin D-deficient mice compared with control mice. Prenatal and postnatal vitamin D supplementation significantly attenuated the development of AHR and decreased pulmonary accumulation of TH2/TH17 cells after coexposure to TRAP and allergen but not to allergen alone. Restoration of normal vitamin D status had no effect on AHR once asthma was already established.

Conclusions: Our data establish that vitamin D confers protection against asthma development specifically in the context of TRAP exposure. Although vitamin D replacement did not reverse established asthma, restoration of normal vitamin D status in early life significantly attenuated the development of AHR in the setting of DEP-exacerbated allergic asthma and reduced numbers of lung TH2/TH17 cells, which portend the development of severe asthma.