Table 4.
Effects of regular vitamin C on the incidence and duration of the common cold a.
| Outcome Participants | No. of Studies | No. of Participants | Effect of Vitamin C (95% CI) | p |
|---|---|---|---|---|
| Incidence of colds b | ||||
| General population | 24 | 10,708 | −3% (−6% to 0%) | |
| People under heavy short-term physical stress | 5 | 598 | −52% (−65% to −36%) | 10−6 |
| Duration of colds | No. of colds | |||
| All studies (≥0.2 g/day) | 31 | 9745 | −9.4% (−13% to −6%) | 10−7 |
| Adults (≥1 g/day) | 13 | 7095 | −8% (−12% to −4%) | 10−4 |
| Children (≥1 g/day) | 10 | 1532 | −18% (−27% to −9%) | 10−5 |
| Severity of colds | No. of colds | |||
| All studies | 16 | 7209 | −0.12 (−0.17 to −0.07) c | 10−6 |
This table summarizes the main findings of the Cochrane review by Hemilä and Chalker (2013) [68,69]. a Regular supplementation of vitamin C means that vitamin C was administered each day over the whole study period. Duration and severity of colds indicates the effects on colds that occurred during the study; b Incidence indicates here the number of participants who had ≥1 cold during the study; c The unit in this comparison is the standard deviation. Thus −0.12 means that symptoms were decreased by 0.12 times the SD of the outcome.