Table 1. Characteristics of Children Included in Study.
| Characteristic | No. (%) | ||
|---|---|---|---|
| Not Breastfed (n = 1989) | Breastfed (n = 4751) | Total (N = 6740) | |
| Age, mean (SD), ya | 11.4 (2.1) | 11.6 (2.1) | 11.6 (2.1) |
| Height, mean (SD), cma | 153.4 (12.9) | 154.2 (12.5) | 153.9 (12.6) |
| Weight, mean (SD), kg | 47.9 (15.6) | 48.7 (15.6) | 48.4 (15.6) |
| Body mass index, mean (SD)b | 19.9 (4.3) | 20.1 (4.8) | 20.0 (4.7) |
| Birth weight, mean (SD), kga | 3.37 (0.49) | 3.41 (0.47) | 3.40 (0.48) |
| Area of residence per person, mean (SD), m2a | 23.6 (9.9) | 22.4 (9.7) | 22.7 (9.8) |
| Exercise, mean (SD), h/wka | 7.3 (6.9) | 7.7 (8.1) | 7.6 (7.7) |
| Boysa | 1070 (53.8) | 2312 (48.7) | 3382 (50.2) |
| Preterm birtha | 150 (7.5) | 188 (4.0) | 338 (5.0) |
| Parental education ≥high school | 1264 (63.6) | 2947 (62.0) | 4211 (62.5) |
| Family income per year, ¥a, | |||
| <5000c | 232 (11.7) | 526 (11.1) | 758 (11.2) |
| 5000-9999d | 255 (12.8) | 621 (13.1) | 876 (13.0) |
| 10 000-29 999e | 644 (32.4) | 1750 (36.8) | 2394 (35.5) |
| 30 000-99 999f | 758 (38.1) | 1679 (35.3) | 2437 (36.2) |
| >100 000g | 100 (5.0) | 175 (3.7) | 275 (4.1) |
| Passive smoke exposure | |||
| Father | 590 (29.7) | 1532 (32.3) | 2122 (31.5) |
| Mother | 186 (9.4) | 422 (8.9) | 608 (9.0) |
| Other | 175 (8.8) | 376 (7.9) | 551 (8.2) |
| Anyone | 951 (47.8) | 2330 (49.0) | 3281 (48.7) |
| Maternal smoking during pregnancy | 15 (0.8) | 39 (0.8) | 54 (0.8) |
| Home coal usea | 170 (8.6) | 506 (10.7) | 676 (10.0) |
| Pet kept in home | 452 (22.7) | 983 (20.7) | 1435 (21.3) |
| Home renovation in past 2 y | 706 (35.5) | 1710 (36.0) | 2416 (35.9) |
| Family history of atopy | 414 (20.8) | 976 (20.5) | 1390 (20.6) |
| Asthma diagnosisa | 160 (8.0) | 300 (6.3) | 460 (6.8) |
| Current asthma | 102 (5.1) | 195 (4.1) | 297 (4.4) |
| Spirometric parameters, mean (SD)a | |||
| FVC, L | 2.6 (0.8) | 2.6 (0.7) | 2.6 (0.8) |
| FEV1, L | 2.4 (0.7) | 2.5 (0.7) | 2.5 (0.7) |
| PEF, L/s | 4.7 (1.5) | 4.8 (1.4) | 4.8 (1.4) |
| MMEF, L/s | 3.3 (1.1) | 3.4 (1.0) | 3.4 (1.1) |
| Lung function statusa | |||
| FVC <85% of predicted value | 269 (13.5) | 490 (10.3) | 759 (11.3) |
| FEV1 <85% of predicted value | 215 (10.8) | 363 (7.6) | 578 (8.6) |
| PEF <75% of predicted value | 166 (8.4) | 292 (6.2) | 458 (6.8) |
| MMEF <75% of predicted value | 216 (10.9) | 418 (8.8) | 634 (9.4) |
Abbreviations: FEV1, forced expiratory volume in the first second of expiration; FVC, forced vital capacity; MMEF, maximum mid expiratory flow rate; PEF, peak expiratory flow rate.
a
Significant difference exists between children who were breastfed and those who were not as tested by χ2 test for categorical variables and t test for continuous variables (P < .05).
b
Calculated as weight in kilograms divided by height in meters squared.
c
Less than US $744.11.
d
US $744.11 to US $1488.08.
e
US $1488.23 to US $4464.54.
f
US $4464.68 to US $14 882.13.
g
Greater than US $14 882.28.