“Vitamin D supplements prevent colds and flu.”
Vitamin D pills do not prevent colds or flu: across 40 trials with more than 61,000 people, they did not clearly lower infection rates.
Taking vitamin D will not keep you from catching colds or the flu. If you take it for another reason, a standard daily dose is fine, but extra vitamin D in winter is not a shield against getting sick.
If you take vitamin D, keep to a standard daily dose and do not raise it during cold and flu season.
Safety note: Too much vitamin D can raise blood calcium, which can lead to kidney damage, kidney stones, confusion and calcium deposits in the heart and lungs. The upper limit for people 9 and older is 4,000 IU a day from all sources, unless a clinician supervises a higher dose.
Forty trials with more than 61,000 people, including two very large trials, found no clear drop in colds, flu or other respiratory infections with vitamin D. Confidence is moderate rather than strong because the pooled result sat close to the line, and an earlier analysis with fewer trials found a slight benefit.
Vitamin D pills do not prevent colds or flu: across 40 trials with more than 61,000 people, they did not clearly lower infection rates. The pooled result was about 6 percent lower odds of infection, a gap small enough to be chance, and it did not change with age, dose or how much vitamin D people had to start with.
A 2021 analysis of fewer trials found about 8 percent lower odds of a respiratory infection with vitamin D. When the same research team added newer trials in 2025, the drop was no longer clear, and the pattern of results suggested that some small trials showing no benefit may be missing, which would make the true effect even smaller. In the D-Health trial of 21,315 Australians aged 60 to 84, a monthly dose of 60,000 IU for up to five years did not lower the chance of a respiratory infection. In the CORONAVIT trial of 6,200 people in the UK, those offered a vitamin D test, and given 800 or 3,200 IU a day for six months if their level was low, were no less likely to get a respiratory infection than people not offered vitamin D (5.7 and 5.0 percent versus 4.6 percent). About 9 in 10 of those tested had low levels. Most trials counted all colds, flu and chest infections together rather than flu alone.
- Jolliffe DA, Camargo CA, Sluyter JD, Aglipay M, Aloia JF, Bergman P, et al.; Martineau AR. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Lancet Diabetes & Endocrinology. 2025;13(4):307-320. DOI: 10.1016/S2213-8587(24)00348-6. PMID: 39993397. PMCID: PMC12056739
- Pham H, Waterhouse M, Baxter C, Duarte Romero B, McLeod DSA, Armstrong BK, et al.; Neale RE. The effect of vitamin D supplementation on acute respiratory tract infection in older Australian adults: an analysis of data from the D-Health Trial. Lancet Diabetes & Endocrinology. 2021;9(2):69-81. DOI: 10.1016/S2213-8587(20)30380-6. PMID: 33444565
- Jolliffe DA, Holt H, Greenig M, Talaei M, Perdek N, Pfeffer P, et al.; Martineau AR. Effect of a test-and-treat approach to vitamin D supplementation on risk of all cause acute respiratory tract infection and covid-19: phase 3 randomised controlled trial (CORONAVIT). BMJ. 2022;378:e071230. DOI: 10.1136/bmj-2022-071230. PMID: 36215226. PMCID: PMC9449358
- MedlinePlus, National Library of Medicine. Vitamin D. Medical Encyclopedia. Review date January 21, 2025; editorial update August 12, 2025