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Pooled review (meta-analysis)

Pooled review of 40 vitamin D trials, 61,589 people: no clear change in infections

Jolliffe and colleagues · The lancet. Diabetes & endocrinology · 2025

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

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What the study found

No difference

Vitamin D did not clearly change the risk of a respiratory infection (OR 0.94, 95% CI 0.88-1.00, p=0.057). No group effects were found by age, starting vitamin D level or dosing. Serious side effects: OR 0.96.

The study at a glance

Type of study
Pooled review (meta-analysis)
Who or what was studied
40 studies, 61,589 people · People of all ages in 40 trials of vitamin D vs placebo
What was tested
Any vitamin D vs placebo or lower-dose vitamin D, any length
What it measured
The question itself: colds, flu and other respiratory infections
Who has a stake
Company stake
One author reports grants from Pharma Nord, DSM Nutritional Products, Cytoplan and Thornton & Ross, makers of supplements.
Journal
The lancet. Diabetes & endocrinology, 2025
Source
PubMed record 39993397. This page is based on the abstract only.

How much this study counts

  • ✓Pools the results of 40 studies with 61,589 people.
  • •A pooled review is only as strong as the studies it pools.
  • ✓Measured the question itself: colds, flu and other respiratory infections.
  • –Company stake: One author reports grants from Pharma Nord, DSM Nutritional Products, Cytoplan and Thornton & Ross, makers of supplements.
  • •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”: The 2025 pooled analysis of 40 placebo trials and 61 589 people found odds of infection of 0.94 with vitamin D; the range, 0.88-1.00, includes no effect.
  • Quoted in “What we found”: Vitamin D did not change how many people had serious side effects: odds of 0.96 in the 2025 pool and 0.97 in the 2021 pool.
  • 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 40 placebo-controlled trials with 61 589 people. Odds of a respiratory infection were 0.94 (0.88-1.00), which includes no effect. No differences by age, starting vitamin D level, dosing frequency or dose size.
  • Marked as a key paper in the research timeline: 2025 update: protection no longer clear across 40 trials.
  • Open item for a person: Overlap: Jolliffe 2021 updates the 2017 trials and Jolliffe 2025 adds new trials to its 43; treat the three pools as one evolving analysis.
  • Open item for a person: Overlap: VITAL (Camargo 2024, 15 804 people) is the large new trial inside the 2025 pool Jolliffe 2025; trial and pool are not independent.

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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