§.01The study, in one paragraph.
A Cochrane team searched CENTRAL, MEDLINE, Embase, CINAHL, Web of Science, the WHO Global Index Medicus and four clinical trial registries through March 2025. They included randomized controlled trials comparing vitamin D to placebo, or higher doses (≥1,000 IU) versus lower (≤1,000 IU), administered from early pregnancy through age 5. The final synthesis pooled 107 trials with 31,521 participants. Outcomes were dichotomous (proportion of children with an ARI healthcare visit) and continuous (mean visits per child), with hypercalcaemia tracked as a safety outcome. They used GRADE to rate the certainty of every conclusion — which is the part that makes Cochrane reviews especially useful.
§.02What the numbers actually show.
The pooled findings, with GRADE certainty:
- Proportion of kids needing an ARI healthcare visit (vs placebo): RR 0.95 (95% CI: 0.91-1.00), P = 0.03. Slight reduction. Low-certainty evidence.
- Mean number of ARI visits per child (vs placebo): MD 0.07 (95% CI: -0.06 to 0.20), P = 0.32. No effect. Moderate-certainty evidence.
- Higher dose vs lower dose, proportion needing visit: RR 0.94 (95% CI: 0.81-1.10), P = 0.46. No benefit from higher doses. Moderate-certainty evidence.
- Hypercalcaemia in children: infrequent in both placebo and vitamin D arms. No clinical safety concern.
Translation: vitamin D supplementation may make children about 5% less likely to have any healthcare visit for a respiratory infection, but does not reduce how many visits each child has. And higher doses do not produce a bigger effect. The certainty of those findings ranges from low to moderate, meaning future high-quality trials could shift them.
§.03What it means in practice.
For a parent or caregiver: the question "should my kid take vitamin D to prevent colds?" gets a more nuanced answer after this review.
If your child has documented vitamin D deficiency (25(OH)D < 20 ng/mL on a blood test): correct it. The AAP recommendation of 400 IU/day for infants and 600 IU/day for children 1-18 stands. Deficiency is associated with worse health outcomes broadly, not just respiratory.
If your child has adequate vitamin D status: this review suggests the marginal benefit of supplementation for preventing respiratory infections is small (~5% relative reduction in visits) and only at the low-certainty level. Adding more vitamin D on top is unlikely to give meaningfully fewer colds.
For pregnant women: hypercalcaemia is rare even at the doses studied, so supplementation during pregnancy looks safe. ACOG and WHO recommend 600 IU/day routinely.
§.04Limitations the authors flagged.
- Outcome definition heterogeneity: different trials defined "ARI healthcare visit" differently — some counted only physician visits, others included emergency room and hospitalisation. This widens the confidence intervals.
- Baseline vitamin D status varied: some trials enrolled deficient children, others did not. Pooling these dilutes the effect for the population with the most to gain.
- Dose ranges: the "higher dose" category included anything ≥ 1,000 IU/day, which spans a wide range. The optimal dose is still undefined for this outcome.
- Low-certainty evidence flag: for the primary positive finding (slight reduction in visits), the GRADE rating is "low." That means future trials could substantially change the estimate.
§.05Where it fits in the broader evidence.
This 2026 Cochrane review reinforces what the Martineau et al. 2017 BMJ meta-analysis already showed in adults: vitamin D supplementation produces a small protective effect against respiratory infections, larger in people who are deficient. For children, the effect is real but small in absolute terms.
The practical implication for our editorial position: fix vitamin D deficiency aggressively if it exists (in pregnancy, infancy, and childhood especially), but do not over-promise that vitamin D will keep kids from getting sick. The honest story is that adequate vitamin D is one of many factors in healthy immune function, not a singular shield.
§.99The bottom line.
The Cochrane review is the highest-quality evidence we have, and it says vitamin D supplementation slightly reduces the proportion of children with an ARI healthcare visit (RR 0.95, low-certainty) but does not reduce the total number of visits per child. Higher doses do not add benefit. The takeaway is not 'vitamin D prevents colds' nor 'vitamin D does nothing' — it is a modest, dose-independent effect that matters most for kids who are deficient. Test first if you can. Supplement for deficiency. Do not assume more is better.
Vitamin D3 (kids version), 30 servings — at the apothecary.
§.RXThe study.
Vitamin D for preventing acute respiratory infections in children up to five years of age.
van Arragon M, Grant CC, Scragg RK et al. — The Cochrane database of systematic reviews, 2026 Apr 27 · DOI: 10.1002/14651858.CD015111.pub2
Reviewed by Dr. Marthe Janssen, PharmD on May 20, 2026. We summarize peer-reviewed research without making medical claims.
Disclaimer: this article is educational only and not medical advice. Statements about supplements have not been evaluated by the FDA. Always discuss new supplements with your prescriber.