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What do systematic reviews say?

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Evidence found and GRADE certainty

948 questions · 998 findings · 100 reviews · Headline outcomes only

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No studies found 233 · 23.3%GRADE not reported 40 · 4%Very low 203 · 20.3%Low 271 · 27.2%Moderate 176 · 17.6%High 75 · 7.5%

Vitamin A vs placebo

Adverse events: yellowing of the skin · healthy people and healthy male physicians

Vitamin A leads to higher adverse events: yellowing of the skin compared with placebo (high certainty).

1 finding from 1 review

Vitamin A vs placebo

Adverse events: minor gastrointestinal symptoms · healthy people and healthy male physicians

Vitamin A leads to higher adverse events: minor gastrointestinal symptoms compared with placebo (high certainty).

1 finding from 1 review

Vitamin A vs placebo

Incidence: all cancers · healthy people and healthy male physicians

Vitamin A showed no clear difference in incidence: all cancers compared with placebo (high certainty).

1 finding from 1 review

Vitamin A vs placebo

Mortality: all cancers · healthy people and healthy male physicians

Vitamin A showed no clear difference in mortality: all cancers compared with placebo (high certainty).

1 finding from 1 review

Vitamin A vs placebo

Mortality: all causes ‐ smokers and asbestos workers · healthy people and healthy male physicians

Vitamin A leads to higher mortality: all causes ‐ smokers and asbestos workers compared with placebo (high certainty).

1 finding from 1 review

Vitamin C vs placebo

Incidence: lung cancer · healthy male physicians, period: 1997 to 2007 and female health professionals, period: 1998 to 2005

Vitamin C showed no clear difference in incidence: lung cancer compared with placebo (moderate certainty).

1 finding from 1 review

Vitamin C vs placebo

Incidence: lung cancer ‐ men · healthy male physicians, period: 1997 to 2007 and female health professionals, period: 1998 to 2005

Vitamin C showed no clear difference in incidence: lung cancer ‐ men compared with placebo (high certainty).

1 finding from 1 review

Vitamin D vs placebo

Ulcer healing (absolute change in individual parameters of ulcer dimensions over time: mean (SD) cm wound length reduction · people with diabetes and foot ulcers

It is very uncertain whether vitamin D changes ulcer healing (absolute change in individual parameters of ulcer… compared with placebo (very low certainty).

1 finding from 1 review

Vitamin D vs placebo

Ulcer healing (absolute change in individual parameters of ulcer dimensions over time: mean (SD) cm wound depth reduction · people with diabetes and foot ulcers

It is very uncertain whether vitamin D changes ulcer healing (absolute change in individual parameters of ulcer… compared with placebo (very low certainty).

1 finding from 1 review

Vitamin D vs placebo

Ulcer healing (absolute change in individual parameters of ulcer dimensions over time: mean (SD) cm wound width reduction · people with diabetes and foot ulcers

It is very uncertain whether vitamin D changes ulcer healing (absolute change in individual parameters of ulcer… compared with placebo (very low certainty).

1 finding from 1 review