https://files.covid19treatmentguidelines.nih.gov/guidelines/covid19treatmentguidelines.pdf
其中自298页起，为关于VC、VD、Zinc的章节，很详细，很长。总结部分如下
Supplements
Last Updated: February 11, 2021
Summary Recommendations
Vitamin C
• There is insufficient evidence for the COVID-19 Treatment Guidelines Panel (the Panel) to recommend either for or against the use of vitamin C for the treatment of COVID-19.
Vitamin D
• There is insufficient evidence for the Panel to recommend either for or against the use of vitamin D for the treatment of COVID-19.
Zinc
• There is insufficient evidence for the Panel to recommend either for or against the use of zinc for the treatment of COVID-19.
• The Panel recommends against using zinc supplementation above the recommended dietary allowance for the prevention of COVID-19, except in a clinical trial (BIII).
Rating of Recommendations: A = Strong; B = Moderate; C = Optional
Rating of Evidence: I = One or more randomized trials without major limitations; IIa = Other randomized trials or subgroup analyses of randomized trials; IIb = Nonrandomized trials or observational cohort studies; III = Expert opinion
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