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

Table 2 Effect of vitamin C on the symptoms of asthmatic children

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	0.004^a)
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	0.7^a)
≥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	0.013^a)
≥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	0.004^a)
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	0.2^a)
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	0.1^b)
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	0.4^c)
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

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.
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.

ISSN: 2045-7022