Vitamin D

Does vitamin D prevent colds and other respiratory infections?

Updated 3 Nov 2026

Short answer

Probably very little, if at all. A 2025 review of 40 trials with 61,589 people found 6% lower odds of a respiratory infection, but the result was not statistically significant.[1] Age, the starting blood level, the dose and how often people took it did not change the result.[1]

What the trials found

Three reviews, by largely the same authors, pooled the trials of vitamin D for respiratory infections:

  • 2017, 25 trials with 10,933 people: 12% lower odds of an infection.[2] The effect was seen with daily or weekly doses, not with large single (bolus) doses.[2]
  • 2021, data from 48,488 people in 43 trials: 61.3% of people on vitamin D had at least one infection, against 62.3% on placebo. The odds were 8% lower.[3] The clearest effect was with daily doses of 400 to 1000 IU, in trials of 12 months or less, and in children aged 1 to 15. But the tests for a difference between these groups were not significant.[3]
  • 2025, 40 trials with 61,589 people: 6% lower odds, not statistically significant.[1]

Why the picture changed

The 2025 review added six new trials, one of them with 15,804 people.[1] With each update the effect became smaller: 12% lower odds in 2017, 8% in 2021, 6% in 2025.[2][3][1] In 2025, the uncertainty range included no effect at all.[1]

In the 2025 review, no group of people did better than others. The result did not depend on age, the starting blood level, the dose or daily versus less frequent dosing.[1]

People with very low levels

The 2017 analysis used the data of each person in the trials. People who started below 25 nmol/L and took daily or weekly doses had 70% lower odds of an infection.[2] In people at or above 25 nmol/L on daily or weekly doses, the odds were 25% lower.[2] The 2025 review did not find that the starting level changed the effect.[1] So whether people with very low levels gain more is still open.

Why it might work

Many tissues have vitamin D receptors, and some of them make active vitamin D from 25(OH)D themselves.[4] Vitamin D takes part in immune function and in reducing inflammation.[4] These are reasons to test it. They do not show that a supplement prevents infections.

Safety in these trials

Serious side effects were as common with vitamin D as with a placebo, in 38 trials.[1] Some trials gave one large dose once a month to once every 3 months.[3] The adult upper limit is 4000 IU (100 µg) a day.[4]

What is still unknown

  • Whether people with very low vitamin D levels benefit more than others.[2][1]
  • Whether the small effect in children holds up in newer trials.[3][1]

More supplements studied for this goal are on the immune support page.[1]

Sources (4)

  1. Vitamin D supplementation to prevent acute respiratory infections: systematic review and meta-analysis of stratified aggregate data. Jolliffe DA, Camargo CA Jr, Sluyter JD, Aglipay M, Aloia JF, Bergman P, et al. Lancet Diabetes Endocrinol, 2025. PMID 39993397
  2. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. Martineau AR, Jolliffe DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, et al. BMJ, 2017. PMID 28202713
  3. Vitamin D supplementation to prevent acute respiratory infections: a systematic review and meta-analysis of aggregate data from randomised controlled trials. Jolliffe DA, Camargo CA Jr, Sluyter JD, Aglipay M, Aloia JF, Ganmaa D, et al. Lancet Diabetes Endocrinol, 2021. PMID 33798465
  4. Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov

More about vitamin d

What is vitamin D?How do you get vitamin D from sunlight and food?What is vitamin D used for?What vitamin D blood level is too low?Is vitamin D safe?Does vitamin D prevent fractures?

For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.