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Table 2 Effect of vitamin C on the symptoms 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 C-ACT (mean) Difference in C-ACT Test for interaction (P)
   Placebo Vitamin C Estimate 95% CI  
All 60 16.57 19.60 3.03 2.53-3.54  
C-ACT at baseline       
13-15 30 15.8 18.1 2.3 1.7-3.0 0.004a)
16-19 30 17.3 21.1 3.7 3.0-4.5  
FEV1/FVC (%)       
< 59 28 16.4 19.3 2.9 2.3-3.6 0.7a)
≥59 32 16.8 19.9 3.1 2.3-3.9  
FEV1 at baseline (L/s)       
< 1.1 29 16.7 20.3 3.6 3.0-4.3 0.013a)
≥1.1 31 16.5 18.9 2.5 1.7-3.2  
Age (yr)       
7.0-8.2 30 16.6 20.3 3.7 3.1-4.3 0.004a)
8.3-10 30 16.5 18.9 2.3 1.5-3.1  
Weight (kg)       
23-28 29 16.6 19.3 2.7 1.9-3.5 0.2a)
29-37 31 16.6 19.9 3.3 2.7-4.0  
Gender       
Girl 22 16.5 19.5 3.0 2.2-3.9 1.0
Boy 38 16.6 19.6 3.0 2.3-3.7  
Dampness exposure       
Never 25 16.8 19.2 2.4 1.4-3.4 0.1b)
During past 1 yr 20 16.3 19.7 3.4 2.6-4.2  
Earlier 14 16.5 20.1 3.6 2.8-4.4  
Smoking by the father       
Never 21 16.5 19.0 2.5 1.6-3.5 0.4c)
Current 22 16.8 19.8 3.0 2.2-3.9  
Ex-smoker 17 16.4 20.0 3.6 2.7-4.6  
Residential area       
Urban 34 16.5 19.5 3.0 2.4-3.7 1.0
Rural 26 16.7 19.7 3.0 2.2-3.9  
  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 = 0.0002 for the baseline C-ACT and P = 0.005 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.