1. Outcomes: chronic asthma.
| Vitamin C supplementation versus control (asthma) | |||||
| Outcome | Studies | N | Age | Study ID | Study reported result |
| Health‐related quality of life | 1 | 201 participants randomised Vitamin C: 95 (72 completed (76%)) Placebo: 106 (82 completed (77%)) | Vitamin C mean: 42 years Placebo mean: 40 years | Fogarty 2003 | No significant difference in HRQL between the groups after 16 weeks treatment as measured by the available SF‐36 data* |
| Asthma exacerbations | 1 | 16 children Vitamin C: 7 No treatment: 9 | Vitamin C mean: 9.3 years (± 2.4) Control mean: 9.2 years (± 1.9) | Anderson 1983 | No exacerbations in either group |
| FEV1 (L) (at one month) | 1 | 60 participants Vitamin C: 30 Placebo: 30 | Vitamin C mean: 48.38 years (± 9.03) Placebo mean: 40.53 years (± 10.48) | Nadi 2012 | No direct comparison between vitamin C and placebo reported. Before versus after treatment comparison in vitamin C (P = 0.65) and in placebo (P = 0.044) |
| FEV1 (ml) (change from 0 to 16 weeks) | 1 | 201 participants randomised Vitamin C: 95 (72 completed (76%)) Placebo: 106 (82 completed (77%)) | Vitamin C mean: 42 years Placebo mean: 40 years | Fogarty 2003 | No significant difference between vitamin C and placebo: MD ‐11 (95% CI ‐92 to 70), P = 0.78 |
| FEV1 (% predicted) | 1 | 10 participants (cross‐over design) | Very limited details in trial report (conference abstract) | O'Sullivan 2000 | No significant change in FEV1 after vitamin C administration (95 ± 2.7% versus 94.2 ± 3.2%) |
| PEFR (L/min) (change from 0 to 16 weeks) AM | 1 | 201 participants randomised Vitamin C: 95 (72 completed (76%)) Placebo: 106 (82 completed (77%)) | Vitamin C mean: 42 years Placebo mean: 40 years | Fogarty 2003 | No significant difference between vitamin C and placebo: MD 0.9 (95% CI ‐11.8 to 13.5), P = 0.89 |
| PEFR (L/min) (change from 0 to 16 weeks) PM | 1 | 201 participants randomised Vitamin C: 95 (72 completed (76%)) Placebo: 106 (82 completed (77%)) | Vitamin C mean: 42 years Placebo mean: 40 years | Fogarty 2003 | No significant difference between vitamin C and placebo: MD 2.2 (95% CI ‐10.0 to 14.3), P = 0.73 |
| Asthma symptoms (change from 0 to 16 weeks) | 1 | 201 participants randomised Vitamin C: 95 (72 completed (76%)) Placebo: 106 (82 completed (77%)) | Vitamin C mean: 42 years Placebo mean: 40 years | Fogarty 2003 | No significant difference between vitamin C and placebo: MD 0 (95% CI ‐0.2 to 0.1), P = 0.33 |
| Adverse events | 1 | 41 participants Vitamin C: 22 Placebo: 19 | Vitamin C mean: 26.5 years (range 15 to 42) Placebo mean: 27.8 years (range 15 to 46) | Anah 1980 | No adverse events in either group |
*Authors note: "SF‐36 data on physical functioning were incomplete and this section was excluded from analysis".
FEV1: forced expiratory volume in one second HRQL: health‐related quality of life PEFR: peak expiratory flow rate