| Methods |
Double‐blind RCT. Regular supplementation trial. Duration 100 days. Identical twins: one group living together and the other living apart. This deals with those living together |
| Participants |
Australian males and females age range 14 to 64 years (mean 25 years). 51 twin pairs living together |
| Interventions |
1 g/d vitamin C. Both groups received a multi‐vitamin tablet containing 70 mg/d vitamin C |
| Outcomes |
Incidence (Analysis 1.1), duration (Analysis 2.1) and severity (Analysis 3.1) |
| Notes |
SD for duration was not published and the SD was calculated from the P value |
| 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 |
"matching of the active and placebo tablets was checked for both appearance and taste" |
