Findings

What do systematic reviews say?

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Evidence found and GRADE certainty

110 questions · 116 findings · 12 reviews

No studies found 42 · 36.2%GRADE not reported 16 · 13.8%Very low 18 · 15.5%Low 20 · 17.2%Moderate 18 · 15.5%High 2 · 1.7%

Vitamin C vs placebo

Incidence of pneumonia Defined as patient admitted to hospital with a diagnosis of pneumonia Dose: 2 g per day · school‐aged children (6 to 15 years) and marine corps recruits (mean age 18.5 years)

It is very uncertain whether vitamin C changes incidence of pneumonia Defined as patient admitted to hospital with… compared with placebo (very low certainty).

1 finding from 1 review

Vitamin C vs placebo

Adverse effects (urticaria) Defined as participants reporting urticaria (hives) Dose: 2 g per day · school‐aged children (6 to 15 years) and marine corps recruits (mean age 18.5 years)

It is very uncertain whether vitamin C changes adverse effects (urticaria) Defined as participants reporting… compared with placebo (very low certainty).

1 finding from 1 review

Vitamin A vs placebo

Incidence of acute URTIs during the study period (the number of acute URTIs over a period of time) · children up to the age of 7 at risk of upper respiratory tract infection

Summary of findings table ‐ Vitamin A supplements showed no clear difference in incidence of acute URTIs during the study period (the number of… compared with placebo (low certainty).

1 finding from 1 review