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Randomized trial · measured the question itself

24-week trial in 189 healthy Danish children: vitamin D cut respiratory infection sick days

Clerico and colleagues · European journal of nutrition · 2025

Original title: Effects of vitamin D supplementation on acute respiratory tract infections in 6-8-year-old children: a randomized clinical trial.

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What the study found

Points to benefit

Children on vitamin D had 17% fewer sick days from respiratory infection (risk ratio, 0.83; 95% CI, 0.76-0.90) and 43% fewer days with infection and fever (RR, 0.57; 95% CI, 0.48-0.67).

The study at a glance

Type of study
Randomized trial
Who or what was studied
189 people · Healthy 6 to 8 year old children in Copenhagen, Denmark
What was tested
20 µg of vitamin D3 a day vs placebo for 24 winter weeks
What it measured
The question itself: colds, flu and other respiratory infections
Daily amount
20 µg a day
How long
24 weeks
Trial registration
NCT03956732
Who has a stake
No stake declared
No conflict of interest stated by the authors.
Journal
European journal of nutrition, 2025
Source
PubMed record 40310565. This page is based on the abstract only.

How much this study counts

  • ✓Randomized: people were put into groups by chance, so the groups start out alike.
  • ✓Compared with a placebo, a dummy treatment.
  • •Medium size: 189 people.
  • •Lasted 24 weeks.
  • ✓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

Each dot is one on-topic paper on this question. Steps near the top answer the question more directly.

↑ Stronger evidence

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

    10

    2 benefit, 8 no difference

    ↑ This study is the ringed dot

  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

Of the other 9 papers on the same step: 1 benefit, 8 no difference. This one found benefit. It differs from most of them.

Other papers on the same step

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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