| Methods |
Double‐blind RCT. Regular supplementation trial |
| Participants |
Male competitive swimmers in Israel. 12 vitamin C; 10 placebo |
| Interventions |
1 g/day vitamin C for 3 months |
| Outcomes |
Incidence of colds. Duration of colds (Analysis 2.1), severity of colds (Analysis 3.1) |
| Notes |
Trial is divided into males and females since there was significant heterogeneity in vitamin C effect (P = 0.003) |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Random sequence generation (selection bias) |
Low risk |
"randomly selected plastic bottle" |
| 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 |
"identical in appearance" |
