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Pooled review (meta-analysis)

Pooled review of trials: vitamin D slightly lowered infection risk and shortened symptoms

Abioye and colleagues · BMJ global health · 2021

Original title: Effect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis.

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

Points to benefit

Vitamin D lowered the risk of respiratory infection (risk ratio 0.97; 95% CI 0.94 to 1.00; p=0.028) and shortened symptoms by 6% (95% CI -9% to -2%).

The study at a glance

Type of study
Pooled review (meta-analysis)
Who or what was studied
Adults in trials of micronutrient supplements
What was tested
Vitamin D, vitamin C, zinc or multiple micronutrients vs control
What it measured
The question itself: colds, flu and other respiratory infections
Who has a stake
No stake declared
No competing interests declared.
Journal
BMJ global health, 2021
Source
PubMed record 33472840. This page is based on the abstract only.

How much this study counts

  • ✓Pools the results of many studies.
  • •A pooled review is only as strong as the studies it pools.
  • ✓Measured the question itself: colds, flu and other respiratory infections.
  • ✓No competing interests declared.
  • •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 pooled review (meta-analysis), 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
  • Summed up in “What reviews found”: Pooled trials of vitamins and minerals in adults; the abstract gives no trial count. Vitamin D lowered infection risk slightly (0.97; 0.94 to 1.00) and shortened symptoms by 6%.
  • Open item for a person: Unknown overlap: abstracts do not say whether Ganmaa 2020, Reyes 2024, Clerico 2025 or Abioye 2021's trials sit inside the Jolliffe pools.

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 two reads differed. The reviewer checked the abstract and kept the first read. 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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