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

Abstract

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/m³ 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/m³, increasingly protective effects >52.5 μg/m³) 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.

Keywords: Asthma; Obesity; Particulate matter; Vitamin D.

Figure 1.. Effect of PM_2.5 on daytime and nighttime asthma symptoms varies by serum 25-OH Vitamin D levels for children with asthma.

Graphs demonstrate the marginal effects of PM_2.5 on daytime (panels a, b) and nighttime (panels c, d) asthma symptoms by vitamin D level, while holding obesity status constant. GEE with AR1 correlation structure and robust standard error estimator was used. Models are fully adjusted by age, sex, caregiver education, season, and ICS use and include the necessary lower-order interaction and main effect terms. The Y-axis represents the odds ratio (OR) for symptoms for each 10 μg/m³ in PM_2.5. The x-axis ranges from the 10th percentile to 90th percentile level of 25-OH vitamin D. At lower 25-OH vitamin D levels (<15.5 ng/mL and <16.4 ng/mL), higher PM_2.5 exposures are increasingly associated with significantly greater risk of daytime and nighttime symptoms, respectively, among obese children (panel b, d). No effect modification was seen among non-obese children (panel a, c).

Figure 2.. Effect of serum 25-OH vitamin D levels on daytime asthma symptoms in obese children with asthma in children exposed to high indoor levels of PM_2.5.

Graphs demonstrate the effect of incremental changes in 25-OH D level (y axis) at each level of PM_2.5 exposure (x-axis). GEE with AR1 correlation structure and robust standard error estimator were used. The model was fully adjusted for age, sex, caregiver education, season, and ICS use, and includes the necessary lower-order interaction and main effect terms. The Y-axis represents the odds ratio (OR) for daytime symptoms for each 1 ng/ml change in 25-OH vitamin D. The x-axis ranges from the 10th percentile to 90th percentile level of PM_2.5. At PM_2.5 concentrations greater than 52.5 μg/ml, higher 25-OH vitamin D levels are associated with a decreased odds ratio of daytime asthma symptoms in obese children.

Figure 3.. Effect of PM_2.5 on peripheral neutrophil percentage varies by serum 25-OH Vitamin D levels for children with asthma.

Graphs are based on the 3-way interaction model between PM_2.5, vitamin D, and obesity, while holding obesity status constant and observing the marginal effect of a change in 25-OH vitamin D level. GEE with exchange correlation structure and robust standard error estimator was used. Models are fully adjusted for age, sex, caregiver education, season, and ICS use, and all models with interaction terms include the necessary lower-order interaction and main effect terms. The Y-axis represents the change in neutrophil percentage for each 10 μg/m³ in PM_2.5. The x-axis ranges from the 10^th percentile to 90^th percentile level of 25-OH vitamin D. At lower 25-OH vitamin D levels (<26.8 ng/mL), higher PM_2.5 exposures are increasingly associated with significantly higher peripheral neutrophil percentage (β_PM2.5 = 0.47) among obese children. No effect modification was seen among non-obese children.