Thursday, October 8, 2026

Evident

PubMed

The claim you checked

Vitamin D supplements prevent winter infections

Verdict

It's complicated

The short answer

Vitamin D might cut chest and throat infections (respiratory tract infection) a little bit, but the results vary and depend on your baseline levels.

What the research says

Pooled trials show a modest drop in chest and throat infections (respiratory tract infection) from vitamin D (Study 1).

Other updates show mixed results and smaller effects in adults (Studies 3, 6).

The adjusted odds ratio was 0.88 (Study 1).

That is about 12% lower odds, a small effect (Study 1).

General groups like children and adults studied in these trials (Study 1).

Still openIt remains unclear what exact blood levels are best for everyone.

The evidence

Based on 8 studies · 5 used for this verdict · 8 strong

Each bar is one study. Taller = stronger kind of study. Solid = used for this verdict. Striped = retracted.

8 studies read, 5 used for this verdict. By study design: 8 strong designs. One bar per study, in the order of the list of studies, taller for a stronger kind of study.

8 pooled analyses · published 2017 to 2025

Read the full breakdown 6 studies

The claim, part by part

  1. Vitamin D supplements prevent winter infections

    They reduce infection risk slightly, but do not lower the risk of them fully (Study 1).

What the evidence shows

A pooled review of 25 randomized trials found vitamin D lowered chest and throat infection (respiratory tract infection) risk (Study 1).

It reported an adjusted odds ratio (how much more likely an outcome was) of 0.88 for all people (Study 1).

Another review reported a risk ratio of 0.97 for sudden chest and throat infections (acute respiratory infection) (Study 3).

A recent update identified six new trials and pooled aggregate data to re-examine the link (Study 7).

Trials covered 11321 people aged from 0 to 95 years taking various doses (Study 8).

How big the effect isThe adjusted odds ratio was 0.88 (Study 1). That is about 12% lower odds, a small effect (Study 1).

Why the verdict is what it is

Large pooled reviews (meta-analyses) of randomized controlled trials provide moderate evidence, though some updates report small or mixed effects in adults (Studies 1, 6, 7).

Who this applies to

General groups like children and adults studied in these trials (Study 1).

And who it does not

People who were not included in the trials or those given single large bolus (one large dose at once) doses (Study 1).

What is still unknown

The optimal blood level for every age group remains unclear (Study 4).

Every sentence above names the studies it rests on. Figures are copied from the abstracts, never worked out from them. Tap a study number to read it.

Studies checked

Ruled = relied on

Open any study for its abstract, how often it has been cited, free full text where there is any, and the studies next to it.

Relied on for the verdict5

  1. 012017

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

    BMJ (Clinical research ed.) · PMID 28202713

  2. 032021

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

    BMJ global health · PMID 33472840

  3. 062024

    A Systematic Review Supporting the Endocrine Society Clinical Practice Guidelines on Vitamin D.

    The Journal of clinical endocrinology and metabolism · PMID 38828942

  4. 072025

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

    The lancet. Diabetes & endocrinology · PMID 39993397

  5. 082019

    Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis.

    Health technology assessment (Winchester, England) · PMID 30675873

Read, not relied on3

  1. 022020

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

    The American journal of tropical medicine and hygiene · PMID 32342851

  2. 042019

    Acute Respiratory Tract Infection and 25-Hydroxyvitamin D Concentration: A Systematic Review and Meta-Analysis.

    International journal of environmental research and public health · PMID 31438516

  3. 052023

    Infections and Autoimmunity-The Immune System and Vitamin D: A Systematic Review.

    Nutrients · PMID 37686873

Searched PubMed for · More on PubMed

Abstract

What happened next

Looking it up on PubMed.

Researchers

Their contact details are usually on the PubMed page. Most researchers don't answer cold emails, but some do.

Open on PubMed

How a check works

  1. Your claim becomes a search. An AI model turns "apple cider vinegar cures diabetes" into the terms researchers actually use.
  2. PubMed answers. That's the U.S. National Library of Medicine's index of medical research, 37 million papers. We take up to 8 of the best matches with their abstracts.
  3. The studies get weighed, not counted. A meta-analysis of many trials outranks one small pilot. A case report about one patient barely counts. The model reads the abstracts and says which studies it relied on.
  4. The verdict is stamped, with rules. "False" needs studies that contradict the claim. Nothing cited means "it's complicated," never a confident answer. Studies that only match the words don't count.
  5. Every verdict says what's still open. Research is rarely finished. The last line names the gap: who the studies left out, how short they ran, or what finding would change the answer.

Reading the evidence meter

Not medical advice. The model can misread an abstract, and PubMed doesn't index everything. Read the studies. Talk to a clinician about your own health.