Vitamin D status modifies the response to indoor particulate matter in obese urban children with asthma.

BACKGROUND: Indoor fine particulate air pollution (PM2.5 ) 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 effects of indoor PM2.5 upon asthma symptoms in urban children.

METHODS: 120 children aged 5-12 years with physician-diagnosed asthma were evaluated at baseline and every 3 months for 9 months. Indoor PM2.5 , 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 3-way interaction effects of 25-OH D, obesity and PM upon asthma symptoms.

RESULTS: Children were of mean (SD) age 9.7 (2.2) years, 36% were obese, and 95% self-reported black race. Mean (SD) PM2.5 indoor exposure was 38.2 (42.9) μg/m3 and 25-OH D was 19.1 (7.5) ng/ml. Three-way interaction models demonstrated significantly greater PM2.5 -associated effects on daytime asthma symptoms only among obese children with low 25-OH D levels (ORPM2.5 =1.26,p =0.049 at vitamin D=15.5 ng/ml, increasingly stronger PM effects at levels<15.5 ng/ml). In homes with increased PM2.5 , higher 25-OH D was associated with decreased symptom odds (e.g., ORVitamin D = 0.87; p=0.049 at PM2.5 = 52.5 μg/m3 , increasingly protective effects >52.5 μg/m3 ) among obese children.

CONCLUSION: Among obese urban children with asthma, low individual 25-OH vitamin D enhanced adverse respiratory effects associated with indoor PM2.5 . In high PM2.5 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.