Table 5.
Effect of vitamin C on the FEV1 levels of asthmatic children
| Subgroup | No. of Children | FEV1 Mean (L/s) |
Change in FEV1 | Test for interaction (P) | ||
|---|---|---|---|---|---|---|
| Placebo | Vitamin C | Estimate | 95% CI | |||
| All | 60 | 1.125 | 1.446 | 28.9% | 27.3-30.4% | |
| C-ACT at baseline | ||||||
| 13-15 | 30 | 1.16 | 1.48 | 27.5% | 25.4-29.6% | 0.07a) |
| 16-19 | 30 | 1.09 | 1.41 | 30.3% | 28.0-32.6% | |
| FEV1/FVC (%) | ||||||
| < 59 | 28 | 1.11 | 1.43 | 29.4% | 27.0-31.9% | 0.5a) |
| ≥59 | 32 | 1.14 | 1.46 | 28.4% | 26.3-30.5% | |
| FEV1 at baseline (L/s) | ||||||
| < 1.1 | 29 | 1.00 | 1.31 | 31.1% | 28.6-33.6% | 0.004a) |
| ≥1.1 | 31 | 1.24 | 1.58 | 26.8% | 25.1-28.5% | |
| Age (yr) | ||||||
| 7.0-8.2 | 30 | 1.00 | 1.31 | 31.1% | 28.7-33.5% | 0.003a) |
| 8.3-10 | 30 | 1.25 | 1.58 | 26.7% | 24.9-28.4% | |
| Weight (kg) | ||||||
| 23-28 | 29 | 1.12 | 1.44 | 29.7% | 27.1-32.3% | 0.3a) |
| 29-37 | 31 | 1.13 | 1.45 | 28.1% | 26.2-30.0% | |
| Gender | ||||||
| Girl | 22 | 1.07 | 1.37 | 28.6% | 25.6-31.6% | 0.8 |
| Boy | 38 | 1.16 | 1.49 | 29.0% | 27.2-30.9% | |
| Dampness exposure | ||||||
| Never | 25 | 1.16 | 1.53 | 32.4% | 30.2-34.6% | 0.001b) |
| During past 1 yr | 20 | 1.11 | 1.42 | 27.6% | 25.9-29.4% | |
| Earlier | 14 | 1.07 | 1.34 | 25.0% | 21.2-28.8% | |
| Smoking by the father | ||||||
| Never | 21 | 1.17 | 1.52 | 30.1% | 28.0-32.2% | 0.4c) |
| Current | 22 | 1.08 | 1.38 | 28.5% | 25.3-31.7% | |
| Ex-smoker | 17 | 1.12 | 1.43 | 27.9% | 24.9-30.9% | |
| Residential area | ||||||
| Urban | 34 | 1.09 | 1.40 | 29.2% | 27.2-31.3% | 0.6 |
| Rural | 26 | 1.17 | 1.50 | 28.4% | 25.8-31.0% | |
a) The test of interaction was calculated by using dichotomized variables for the C-ACT, FEV1/FVC ratio, FEV1, age, and weight (cut points at the medians). The test of interaction by using the continuous variables gives P = 0.2 for the baseline C-ACT and P = 0.001 for age.
b) The test of interaction is restricted to the "Never" and "During past 1 yr" subgroups. One child who was exposed to dampness both "During past 1 yr" and "Earlier" is excluded from this subgroup comparison.
c) The test of interaction is restricted to the "Never" and "Current" subgroups.