Table 1 Characteristics of the included trials
From: Vitamin C and common cold-induced asthma: a systematic review and statistical analysis
| Study | Item | Description |
|---|---|---|
| Anah et al. 1980[27] | Participants | 41 asthmatic subjects attending an asthma clinic in Nigeria. All had had asthma for at least 4 yrs. The participants had histories of increased asthma attacks during the rainy season. In all cases their attacks were precipitated by respiratory infections, which started with a sore throat and a dry cough. The trial was conducted during the rainy season. Patients with bronchitis were excluded. 22 M, 19 F; age 15 to 46 y (mean 27 y); 22 vit C 19 placebo. |
| Duration | 14 wk | |
| Intervention | 1 g/d vit C or a placebo for 14 wk. | |
| Outcome | Frequency of asthma attacks. “Severe attacks” indicate those that needed emergency attendance at the hospital; “moderate attacks” those that necessitated the use of inhalers more frequently, and “mild attacks” those that caused some increase in wheezing and breathlessness. | |
| Notes | See calculations in Additional files2 and3. | |
| Schertling et al. 1990[30, 31] | Participants | 29 Participants with a diagnosis of infection-related asthma in former East-Germany. Patients with acute and serious purulent infections were excluded. 18 M, 11 F; age 18 to 60 y. |
| Duration | Total duration 5 wk, composed of 2 periods of 2 wk intervention and a 1 wk washout between them. | |
| Intervention | 5 g/d vit C or placebo for 1 wk before the histamine sensitivity test in the middle of the 2 wk intervention. Washout 1 wk between the 2-wk intervention phases. | |
| Outcomes | 1) Sensitivity to histamine: positive result indicates that exposure to <1 μmol histamine increased respiratory tract resistance by 50%. 2) Asthma symptom score, 3) PEF | |
| Notes | See calculations in Additional file2. The histamine sensitivity data are reported for 23 participants. There is no description for the missing data. | |
| Bucca et al. 1989[25, 26] | Participants | 9 members of hospital staff in Italy with a negative history of asthma and atopy. All suffered from the common cold with cough on the first vit C test day, and all had recovered on the second vit C test day 6 wk later. 5 M, 4 F; age 18 to 48 y (mean 29 y). |
| Duration | Two study days separated by 6 wk. | |
| Intervention | Single dose 2 g of vit C. | |
| Outcome | PC20 was measured at baseline and 1 h after vit C administration on both study days. | |
| Notes | See calculations in Additional files2 and3. |