| Methods |
Double‐blind RCT. Regular supplementation trial. Duration 6 weeks before and 2 weeks after the race |
| Participants |
South Africa. Ultra marathon runners. 13 vitamin C; 19 placebo |
| Interventions |
0.25 g/d vitamin C |
| Outcomes |
Incidence (Analysis 1.1) |
| Notes |
1/4 of those who reported respiratory symptoms in the vitamin C group, and 8/13 of those who reported respiratory symptoms in the placebo group, reported that their respiratory symptoms were severe (P = 0.08) |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
Randomised |
| Allocation concealment (selection bias) |
Low risk |
Double‐blind |
| Blinding of participants and personnel (performance bias)
All outcomes |
Low risk |
Double‐blind |
| Blinding of outcome assessment (detection bias)
All outcomes |
Low risk |
Double‐blind |
| Incomplete outcome data (attrition bias)
All outcomes |
Low risk |
|
| Vitamin C and placebo indistinguishable? |
Low risk |
"placebo was identical in form to the ascorbic acid" |
