Digestery
Everyday supplements › Vitamin D and Infections › Studies

Pooled review (meta-analysis)

Pooled review of 25 trials found vitamin D lowered the odds of respiratory infection

Martineau and colleagues · BMJ (Clinical research ed.) · 2017

Original title: Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.

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 odds of a respiratory infection (adjusted odds ratio 0.88, 95% CI 0.81 to 0.96). Benefit was seen with daily or weekly doses (0.81) but not with bolus doses (0.97), and was larger when starting level was <25 nmol/L (0.30).

The study at a glance

Type of study
Pooled review (meta-analysis)
Who or what was studied
25 studies, 10,933 people · People aged 0 to 95 years in 25 placebo-controlled trials
What was tested
Vitamin D3 or D2 pills of any dose and length, vs placebo
What it measured
The question itself: colds, flu and other respiratory infections
Who has a stake
No stake declared
No competing interests declared; funded by the UK National Institute for Health Research.
Journal
BMJ (Clinical research ed.), 2017
Source
PubMed record 28202713. This page is based on the abstract only.

How much this study counts

  • ✓Pools the results of 25 studies with 10,933 people.
  • •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
  • Quoted in “What we found”: Earlier pools found slightly lower odds of infection: 0.88 across 25 trials in 2017, and 0.92 in 2021 (61.3% vs 62.3% of people infected).
  • Part of the finding “Pooled trials: a small benefit that faded”.
  • Part of the finding “Daily dosing and low starting levels: mixed answers”.
  • Summed up in “What reviews found”: Pooled individual data from 25 trials and 10 933 people. Odds of infection were 0.88 with vitamin D. Benefit came with daily or weekly doses, not bolus doses, and was largest when starting levels were under 25 nmol/L.
  • Marked as a key paper in the research timeline: 2017: individual-data pooling of 25 trials finds benefit.
  • Open item for a person: Duplicate: Martineau 2017 and Martineau 2019 report the same individual-data analysis (25 trials, PROSPERO CRD42014013953). Counted once.
  • Open item for a person: Disclosure mismatch: Martineau 2017 declares no relevant ties; the same analysis Martineau 2019 lists GSK, Pfizer, Sanofi, Vifor and Laboratoires SMB. Check.

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
Not yet. Required before search engines may list this page.

Spot an error? Email a flag with a link to your source, or use the form on the question page.