Table 1.
Characteristics of Study Participants
| Covariate | Control (n = 327) | Case (n = 351) |
|---|---|---|
| Age (years) | 10.5 (2.7) | 10.0 (2.6)* |
| Sex (male) | 159 (48.6) | 201 (57.3)* |
| BMI, z-score | 0.5 (1.1) | 0.7 (1.2) |
| Annual household income <$15,000 | 196 (62.8) | 225 (65.4) |
| No private or employer-based health insurance | 205 (62.7) | 239 (68.1) |
| Breastfed | ||
| Never | 142 (44.4) | 159 (45.6) |
| ≤6 months | 152 (47.5) | 144 (41.3) |
| >6 months | 26 (8.1) | 46 (13.2) |
| Parental asthma | 103 (31.7) | 232 (66.3)* |
| Early life exposure to SHS | 131 (41.9) | 174 (51.6)* |
| Outdoor activitya | 240 (73.4) | 268 (76.4) |
| Vitamin D insufficiency (25[OH]D <30 ng/mL) | 136 (46.4) | 135 (43.4) |
| Dietary score | 0.9 (1.0)* | 0.6 (1.0)* |
| Atopy (≥1 positive allergen-specific IgE) | 143 (49.8) | 210 (68.9)* |
| Total IgE (IU/mL) | 2.2 (0.7) | 2.5 (0.9)* |
| Interleukin-17Fb | 0.8 (1.1) | 1.1 (1.0)* |
| Prebronchodilator FEV1 (L) | ||
| %Predicted | 97.8 (15.0) | 92.9 (15.3)** |
| z-Score | −0.17 (1.25) | −0.58 (1.25)** |
| Prebronchodilator FVC (L) | ||
| %Predicted | 104.8 (18.0) | 102.1 (15.8) |
| z-Score | 0.40 (1.56) | 0.17 (1.38) |
| Prebronchodilator FEV1/FVC | ||
| Ratio (%) | 83.5 (9.0) | 80.9 (9.0)** |
| z-Score | −0.82 (1.27) | −1.19 (1.16)** |
| At least 1 severe asthma exacerbation in the prior year | 96 (27.4) | |
| At least 1 hospitalization for asthma in the prior year | 75 (21.4) | |
Data are presented as number (percentage) for binary variables or mean (SD) for continuous variables. Percentages were calculated for children with complete data.
a
At least a moderate amount of outdoor activity including playing, practicing sports, and walking.
b
Data were log10 transformed.
*
P < 0.05; **P < 0.01 for the comparison between control and case groups (conducted using 2-sample t-tests or χ2 tests, as appropriate).
BMI, body mass index; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; SD, standard deviation; SHS, second-hand smoke.