Micronutrient | Subgroup | Effect on occurrence of infection | Effect on duration of symptoms | ||
RR (95% CI) | P value | Percent diff (95% CI) | P value | ||
Vitamin D | Main | 0.97 (0.94 to 1.00) | 0.028 | −6 (−9 to –2) | 0.003 |
Common cold outcome* | 0.93 (0.84 to 1.02) | 0.12 | NR | ||
Well-defined outcome*,‡ | 0.82 (0.68 to 1.00) | 0.046 | −6 (−10 to –2) | 0.35 | |
Serum 25(OH)D, nmol/L | |||||
Not deficient, ≥25 | 0.98 (0.93 to 1.02) | 0.85 | Not est | ||
Deficient, <25 | 0.92 (0.53 to 1.61) | ||||
Daily dose, IU | |||||
0 | 1.01 (0.94 to 1.09) | 0.17 | −10 (−23 to 4) | 0.54 | |
>0 to <2000 | 0.97 (0.95 to 1.00) | −6 (−10 to –2) | |||
≥2000 | 0.90 (0.81 to 1.01) | −2 (−22 to 26) | |||
Weekly dose, IU | |||||
0 | 0.97 (0.94 to 0.99) | 0.06 | −0.5 (−9 to 8) | 0.22 | |
>0 to 20 000 | 0.70 (0.50 to 0.99) | −7 (−11 to –3) | |||
Monthly dose, IU† | |||||
0 | 0.94 (0.89 to 0.98) | 0.06 | −6 (−10 to –2) | 0.28 | |
>0 to <60 000 | 0.95 (0.92 to 0.98) | −4 (−9 to –0.1) | |||
≥60 000 | 0.99 (0.96 to 1.03) | 0 (−11 to 11) | |||
Loading dose, IU | |||||
0 | 0.89 (0.83 to 0.96) | 0.012 | −6 (−10 to –2) | 0.41 | |
>0 to <60 000 | 0.92 (0.87 to 0.97) | −5 (−9 to –0.6) | |||
≥60 000 | 0.98 (0.95 to 1.02) | −2 (−12 to 9) | |||
Dosing regimen, IU | |||||
Loading, 0 | |||||
Daily, <2000 | 0.91 (0.94 to 0.98) | 0.005 | −5 (−18 to 8) | 0.92 | |
Daily, ≥2000 | 0.85 (0.75 to 0.96) | 2 (−26 to 30) | |||
Loading, >0 to <60 000 | |||||
Daily, <2000 | 0.54 (0.34 to 0.85) | Not est | |||
Daily, ≥2000 | 0.51 (0.31 to 0.82) | Not est | |||
Loading, ≥60 000 | |||||
Daily, <2000 | 0.99 (0.96 to 1.02) | −3 (−20 to 13) | |||
Daily, ≥2000 | 0.93 (0.83 to 0.98) | 3 (−30 to 36) | |||
Mean Age | |||||
<40 | 0.94 (0.87 to 1.01) | 0.30 | −7 (−11 to –3) | 0.09 | |
40 to <65 | 0.97 (0.94 to 0.99) | 1 (−7 to 9) | |||
>65 | 0.97 (0.94 to 0.99) | 8 (-8 to 25) | |||
Sex | |||||
Female | 0.92 (0.87 to 0.98) | 0.73 | −2 (−21 to 16) | 0.43 | |
Male | 0.92 (0.87 to 0.98) | −13 (−28 to 1) | |||
Continent | |||||
Africa | NR | 0.08 | NR | 0.50 | |
Asia | 1.02 (0.96 to 1.08) | −0.7 (-15 to 14) | |||
Australia | 0.98 (0.95 to 1.01) | −3 (−12 to 7) | |||
Europe | 0.94 (0.90 to 0.98) | −4 (−10 to 0.9) | |||
North America | 0.91 (0.84 to 0.98) | −6 (−10 to –2) | |||
South America | NR | NR | |||
Length of trial | |||||
<2 weeks | NR | 0.08 | NR | 0.12 | |
2 weeks to <3 months | 0.93 (0.88 to 0.98) | −7 (−11 to –3) | |||
3 months to <1 year | 0.94 (0.90 to 0.98) | −5 (−9 to –0.5) | |||
>1 year | 0.96 (0.94 to 0.99) | 2 (−9 to 12) |
NR: Not relevant; that is, no primary studies that met the criteria. All studies were conducted in high-income countries.
Not est: Not estimated; that is meta-analysis was not done.
*Sensitivity analysis.
†Includes studies that provided 2 monthly doses, categorised in monthly equivalents.
‡Outcome was defined based on clinical diagnosis and laboratory testing. Cases based on self-report were excluded.