Table 1

Vitamin D—summary of meta-analyses findings—main and subgroups

MicronutrientSubgroupEffect on occurrence of infectionEffect on duration of symptoms
RR (95% CI)P valuePercent diff (95% CI)P value
Vitamin DMain0.97 (0.94 to 1.00)0.028−6 (−9 to –2)0.003
Common cold outcome*0.93 (0.84 to 1.02)0.12NR
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, ≥250.98 (0.93 to 1.02)0.85Not est
 Deficient, <250.92 (0.53 to 1.61)
Daily dose, IU
 01.01 (0.94 to 1.09)0.17−10 (−23 to 4)0.54
 >0 to <20000.97 (0.95 to 1.00)−6 (−10 to –2)
 ≥20000.90 (0.81 to 1.01)−2 (−22 to 26)
Weekly dose, IU
 00.97 (0.94 to 0.99)0.06−0.5 (−9 to 8)0.22
 >0 to 20 0000.70 (0.50 to 0.99)−7 (−11 to –3)
Monthly dose, IU†
 00.94 (0.89 to 0.98)0.06−6 (−10 to –2)0.28
 >0 to <60 0000.95 (0.92 to 0.98)−4 (−9 to –0.1)
 ≥60 0000.99 (0.96 to 1.03)0 (−11 to 11)
Loading dose, IU
 00.89 (0.83 to 0.96)0.012−6 (−10 to –2)0.41
 >0 to <60 0000.92 (0.87 to 0.97)−5 (−9 to –0.6)
 ≥60 0000.98 (0.95 to 1.02)−2 (−12 to 9)
Dosing regimen, IU
 Loading, 0
  Daily, <20000.91 (0.94 to 0.98)0.005−5 (−18 to 8)0.92
  Daily, ≥20000.85 (0.75 to 0.96)2 (−26 to 30)
 Loading, >0 to
<60 000
  Daily, <20000.54 (0.34 to 0.85)Not est
  Daily, ≥20000.51 (0.31 to 0.82)Not est
 Loading, ≥60 000
  Daily, <20000.99 (0.96 to 1.02)−3 (−20 to 13)
  Daily, ≥20000.93 (0.83 to 0.98)3 (−30 to 36)
Mean Age
 <400.94 (0.87 to 1.01)0.30−7 (−11 to –3)0.09
 40 to <650.97 (0.94 to 0.99)1 (−7 to 9)
 >650.97 (0.94 to 0.99)8 (-8 to 25)
Sex
 Female0.92 (0.87 to 0.98)0.73−2 (−21 to 16)0.43
 Male0.92 (0.87 to 0.98)−13 (−28 to 1)
Continent
 AfricaNR0.08NR0.50
 Asia1.02 (0.96 to 1.08)−0.7 (-15 to 14)
 Australia0.98 (0.95 to 1.01)−3 (−12 to 7)
 Europe0.94 (0.90 to 0.98)−4 (−10 to 0.9)
 North America0.91 (0.84 to 0.98)−6 (−10 to –2)
 South AmericaNRNR
Length of trial
 <2 weeksNR0.08NR0.12
 2 weeks to <3 months0.93 (0.88 to 0.98)−7 (−11 to –3)
 3 months to <1 year0.94 (0.90 to 0.98)−5 (−9 to –0.5)
 >1 year0.96 (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.