Vitamin D Status Modifies the Response to Indoor Particulate Matter in Obese Urban Children with Asthma.

Background: Indoor fine particulate air pollution (PM _2.5 ) is linked to asthma morbidity; however, whether vitamin D status influences individual susceptibility to airborne exposures is unclear.
Objective: We aimed to determine if vitamin D modifies the effects of indoor PM _2.5 on asthma symptoms in urban children.
Methods: A total of 120 children aged 5 to 12 years with physician-diagnosed asthma were evaluated at baseline and every 3 months for 9 months. Indoor PM _2.5 , serum 25-hydroxy vitamin D (25-OH D) levels, and asthma symptoms were simultaneously assessed at each time point. Adjusting for confounders, generalized estimating equations assessed the 3-way interaction effects of 25-OH D, obesity, and PM on asthma symptoms.
Results: Children were of mean (standard deviation [SD]) age 9.7 (2.2) years, 36% were obese, and 95% self-reported black race. Mean (SD) PM _2.5 indoor exposure was 38.2 (42.9) μg/m ³ and 25-OH D was 19.1 (7.5) ng/mL. Three-way interaction models demonstrated significantly greater PM _2.5 -associated effects on daytime asthma symptoms only among obese children with low 25-OH D levels (odds ratio [OR] _PM2.5  = 1.26, P = .049 at vitamin D = 15.5 ng/mL, increasingly stronger PM effects at levels <15.5 ng/mL). In homes with increased PM _2.5 , higher 25-OH D was associated with decreased symptom odds (eg, OR _{Vitamin D}  = 0.87; P = .049 at PM _2.5  = 52.5 μg/m ³ , increasingly protective effects >52.5 μg/m ³ ) among obese children.
Conclusions: Among obese urban children with asthma, low individual 25-OH D enhanced adverse respiratory effects associated with indoor PM _2.5 . In high PM _2.5 environments, 25-OH D was protective against asthma symptoms. Optimizing vitamin D status in children may help reduce asthma morbidity driven by indoor air pollution.
(Copyright © 2019 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)