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Table 3 Findings of the included trials

From: Vitamin C and common cold-induced asthma: a systematic review and statistical analysis

Study Outcome P (2-tail) for the difference Estimate of vitamin C effect (95% CI) Notes
Anah et al. 1980[27] Incidence of all asthma attacks: 0.019 RR = 0.22 (0.06 to 0.81) All asthma attacks: 9/22 and 35/19 (attacks/persons) in vit C and placebo groups, respectively. See Additional files2 and3 for the calculations.
  Incidence of severe and moderate asthma attacks: 0.003 RR = 0.11 (0.02 to 0.48) Severe and moderate asthma attacks: 3/22 and 23/19 (attacks/persons) in vit C and placebo groups, respectively. See Additional files2 and3 for the calculations.
Schertling et al. 1990[30, 31] Proportion of participants who were sensitive to histamine: 0.0005 52 percentage points decrease (25 to 71) The P-value was calculated from the discordant observations: 12 were sensitive to histamine in the placebo phase but not in the vit C phase; 0 were sensitive to histamine in the vit C phase but not in the placebo phase. See Additional file2 for the calculations.
  Asthma symptom score: 0.12 Placebo: 0.72, Vit C: 0.65 Scale 0 to 3; 0 indicates no symptoms. The P-value was calculated by Schertling et al.[30, 31].
  PEF: 0.12 Placebo: 400 L/min, Vit C: 409 L/min The P-value was calculated by Schertling et al.[30, 31].
Bucca et al. 1989[25, 26] Histamine PC20: 0.0003 3.2 fold increase in PC20, (2.0 to 5.1 fold) Vit C increased histamine PC20 geometric mean from 7.8 to 25.1 mg/ml. See Additional files2 and3 for the calculations.
  Interaction between the vitamin C effect and the common cold: 0.003   Interaction test for the vit C effect on PC20 (before/after vit C) and the presence of the common cold (yes/no). See Additional file2 for the calculations.
  1. Abbreviations:
  2. CI: Confidence Interval.
  3. PC20: Concentration of histamine needed for a 20% FEV1 decrease.
  4. PEF: Peak Expiratory Flow.
  5. RR: Rate Ratio.