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Systematic review

Review of 20 trials in healthy adults found no clear cold prevention from supplements

Wang and colleagues · The American journal of tropical medicine and hygiene · 2020

Original title: Zinc Supplementation Reduces Common Cold Duration among Healthy Adults: A Systematic Review of Randomized Controlled Trials with Micronutrients Supplementation.

Under review. A person has not yet checked this summary against the paper. It is written from the PubMed abstract. Until a person checks it, search engines are asked not to list this page.

What the study found

No difference

Micronutrients except vitamin C may not prevent colds or reduce symptom severity. Zinc may cut cold length by 2.25 days (95% CI: -3.39, -1.12). Vitamin D results are not given on their own.

The study at a glance

Type of study
Systematic review
Who or what was studied
20 studies · Healthy adults in 20 trials of single micronutrients
What was tested
Zinc, vitamin D, vitamins A and E by mouth, vs control
What it measured
The question itself: colds, flu and other respiratory infections
Who has a stake
No disclosure in PubMed
No company tie mentioned; no clear conflict statement.
Journal
The American journal of tropical medicine and hygiene, 2020
Source
PubMed record 32342851. This page is based on the abstract only.

How much this study counts

  • •Sums up 20 studies found with a set search method, without pooling the numbers.
  • ✓Measured the question itself: colds, flu and other respiratory infections.
  • •The PubMed record has no conflict-of-interest statement.
  • •Summarized from the PubMed abstract only. The full paper may hold details the abstract leaves out.

✓ Strength– Limit• Note

These points come from fixed rules about the type of study, its size and length, what it measured, and who has a stake. Every study on Digestery gets the same rules.

Where this study sits

This paper is not on the ladder. It is a systematic review, and reviews and opinion pieces discuss studies that are already counted on the steps below.

↑ Stronger evidence

  1. Trials in people: colds, flu and chest infections

    10

    2 benefit, 8 no difference

  2. Trials in people: other measures

    5

    1 benefit, 1 mixed, 2 no difference, 1 harm

  3. Trials in people: lab tests or safety

    1

    1 no difference

  4. Population studies

    1

    1 no difference

  5. Blood levels and genes

    4

    3 benefit, 1 no difference

↓ Weaker evidence

  • Points to benefit
  • Mixed
  • No difference
  • No direction
  • Points to harm

How it fits with the other research

The short answer to “Does vitamin D prevent colds and infections?”

Not clearly; any effect looks small.

Confidence: low. Based on 33 on-topic papers.

Read the full answer
  • Open item for a person: Unsure on relevance: Wang 2020 set relevant (vitamin D not reported alone); Mayan 2015 reports no vitamin D effect on colds; 41023725 set off-topic.

Other reviews on this question

See all 33 studies on this question

How this page was made

Label

First read of the abstract
Claude Sonnet
Independent second read
Claude Haiku
Differences settled
The reviewer corrected 1 field after reading the abstract. Claude Opus 5.5.
Headline
Claude Sonnet, from the checked study record. A script checked its numbers and wording.
Numbers
Checked against the abstract by a script
“How much this study counts”
Fixed rules, the same for every study
Source check by a person
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