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 equationsassessed the 3-wayinteraction 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 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.