Cohen 1997.
| Methods | Randomised, double‐blind trial, cross‐over design | |
| Participants | 20 patients with asthma received both vitamin C and placebo in a randomised, cross‐over design
Mean age 13.8 (7 to 28)
Sex: 13 males (65%) Reported as: all participants demonstrated exercise‐induced asthma (EIA) by having a decline of at least 15% in their forced expiratory volume in 1 second after a standard exercise test on a motorised treadmill (model Q50, Quinton Instrument Co, Seattle, Wash). The patients were advised to refrain from taking their regular medication, which consisted of inhaled steroids, antihistamines and bronchodilators, 12 hours before the test Baseline FEV1 (L) (before exercise): 2.36 (0.85); baseline FEV1 (L) (after exercise): 1.74 (0.72) Baseline FEV1 (% predicted) (before exercise): 86 (12); baseline FEV1 (% predicted) (after exercise): 63 (13) The setting was a university hospital in Israel |
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| Interventions | Reported as: 2 g of oral ascorbic acid versus placebo 1 hour before a 7‐minute treadmill exercise session. 8 minutes after exercise pulmonary function tests were performed. 1 week later participants received the alternative intervention | |
| Outcomes | Development of exercise‐induced asthma (EIA), FEV1 (L) and FEV1 (% predicted) | |
| Notes | Summary of FEV1; a single large dose of ascorbic acid before exercise prevented the development of EIA in 9 of 20 patients and reduced the airways’ responsiveness to exercise in 2 other patients Funding source not reported |
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| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| Random sequence generation (selection bias) | Unclear risk | Not reported |
| Allocation concealment (selection bias) | Unclear risk | Not reported |
| Blinding of participants and personnel (performance bias) All outcomes | Unclear risk | Described as double‐blind but method of blinding (whether it was a matched placebo) is unclear in trial report |
| Blinding of outcome assessment (detection bias) All outcomes | Unclear risk | Described as double‐blind but method of blinding (whether it was a matched placebo) is unclear in trial report |
| Incomplete outcome data (attrition bias) All outcomes | Low risk | Information included in trial report from all 20 participants |
| Selective reporting (reporting bias) | Unclear risk | No indication of reporting bias |