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Table 5 Effect of vitamin C on the FEV1 levels of asthmatic children

From: Vitamin C and asthma in children: modification of the effect by age, exposure to dampness and the severity of asthma

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%  
  1. 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.
  2. 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.
  3. c) The test of interaction is restricted to the "Never" and "Current" subgroups.