Micronutrient | Subgroup | Effect on occurrence of infection | Effect on duration of symptoms | ||
RR (95% CI) | P value | Percent diff (95% CI) | P value | ||
Vitamin C | Main | 0.96 (0.93 to 0.99) | 0.01 | −9 (−16 to –2) | 0.014 |
Common cold outcome* | 0.96 (0.93 to 0.99) | 0.022 | −9 (−16 to –2) | 0.007 | |
Daily dose, mg | |||||
≥2000 | 0.94 (0.87 to 1.00) | 0.63 | −5 (−17 to 7) | 0.62 | |
1000 to <2000 | 0.95 (0.91 to 0.98) | −7 (−14 to –0.1) | |||
500 to <1000 | 0.95 (0.92 to 0.99) | −8 (−15 to –0.1) | |||
<500 | 0.96 (0.91 to 1.00) | NR | |||
Loading dose, mg | |||||
>4000 | 0.95 (0.92 to 0.98) | 0.18 | −10 (−36 to 16) | 0.92 | |
>2000–4000 | 0.96 (0.93 to 0.99) | −9 (−21 to 3) | |||
>1000–2000 | 0.98 (0.94 to 1.02) | −9 (−16 to –2) | |||
<1000 | 1.02 (0.93 to 1.11) | NR | |||
Mean age, years | |||||
<40 | 0.98 (0.93 to 1.03) | 0.56 | −5 (−21 to 11) | 0.81 | |
40 to <65 | 0.91 (0.72 to 1.16) | −9 (−39 to 21) | |||
>65 | NR | −13 (−74 to 48) | |||
Sex | |||||
Female | 1.11 (0.95 to 1.30) | 0.049 | −13 (−28 to 1) | 0.43 | |
Male | 0.82 (0.70 to 0.96) | −2 (−21 to 16) | |||
Continent | |||||
Africa | 0.81 (0.65 to 1.02) | 0.14 | 1 (−16 to 19) | 0.22 | |
Asia | 0.85 (0.72 to 1.00) | −2 (−15 to 11) | |||
Australia | 0.89 (0.78 to 0.99) | −5 (−14 to 3) | |||
Europe | 0.92 (0.87 to 0.98) | −9 (−16 to 2) | |||
North America | 0.96 (0.93 to 0.99) | −12 (−21 to 3) | |||
South America | NR | −16 (−28 to –3) | |||
Country income class | |||||
High | 0.96 (0.93 to 0.99) | 0.017 | −8 (−16 to –1) | 0.77 | |
Middle | 0.65 (0.47 to 0.89) | −11 (−30 to 7) | |||
Length of trial | |||||
<2 weeks | NR | 0.14 | −16 (−36 to 3) | 0.30 | |
2 weeks to <3 months | 0.93 (0.83 to 1.03) | −13 (−29 to 3) | |||
3 months to <1 year | 0.77 (0.60 to 0.98) | −3 (−22 to 17) | |||
>1 year | 0.47 (0.20 to 1.14) | 26 (–42 to 93) |
NR: Not relevant; that is, no primary studies that met the criteria.
*Sensitivity analysis.