Vitamin D

What is vitamin D used for?

Updated 3 Nov 2026

Short answer

Vitamin D prevents rickets in children and osteomalacia, a softening of the bones, in adults.[1] In large trials, mostly of adults who lived at home and were not at high risk, vitamin D alone did not prevent fractures, heart disease or cancer.[2][3] Its effect on respiratory infections was small or none.[4]

What it does for certain

The body needs vitamin D to absorb calcium from food. Too little for a long time causes rickets in children and osteomalacia in adults. Both mean soft, weak bones that can hurt and bend.[1]

US experts consider a blood level of 25(OH)D of 50 nmol/L (20 ng/mL) or more enough for most people. Below 30 nmol/L (12 ng/mL), the risk of deficiency rises.[1] More about the test: What vitamin D blood level is too low?

Breastfed babies are one group with trial data on blood levels. In a 2020 Cochrane review, 400 IU a day raised their blood level by about 23 nmol/L. A level below 50 nmol/L became 43% less common. The certainty of this evidence was low.[5] Details: Vitamin D for breastfed babies and the growth and development page.

Bones and fractures

A 2026 review in the BMJ pooled 69 trials with 153,902 adults. In 36 of them, vitamin D alone did not change the risk of a fracture, with high certainty.[2] With calcium, the risk was 9% lower in 15 trials. The authors judged this to be little to no benefit.[2] Full answer: Does vitamin D prevent fractures? More on the bone and joint page.

Respiratory infections

A 2025 review pooled 40 trials with 61,589 people. The odds of a respiratory infection were 6% lower with vitamin D, but the result was not statistically significant.[4] Earlier reviews with fewer trials had found a small benefit.[6][7] Full answer: Does vitamin D prevent colds and other respiratory infections? More on the immune support page.

Autoimmune disease

The VITAL trial gave 25,871 US adults 2000 IU of vitamin D a day or a placebo for a median of 5.3 years. It enrolled men aged 50 or older and women aged 55 or older.[8] New autoimmune disease, such as rheumatoid arthritis or psoriasis, was found in 123 people on vitamin D and 155 on placebo. This was 22% fewer.[8] This result comes from one trial.[8]

Heart, cancer, mood and weight

In VITAL, the same dose did not lower the risk of cancer, or of heart attack, stroke and death from heart disease.[3] A 2022 review for the US Preventive Services Task Force pooled up to 27 trials. It found no effect of vitamin D on heart disease, cancer or death from any cause.[9] More on the heart health page.

For mood, a 2024 review of 31 trials found a small drop in depression scores, mostly in trials of 24 weeks or less.[10] See Does vitamin D help with depression? and the stress and mood page. Trials did not find that vitamin D helps people lose weight.[1]

Why the large trials found so little

Most people in VITAL already had enough vitamin D. Only 2.4% started below 30 nmol/L.[1] VITAL did not select people for low vitamin D, low bone mass or osteoporosis.[11]

In a 2017 analysis of respiratory infection trials, people who started below 25 nmol/L and took daily or weekly doses had 70% lower odds of an infection.[6] The 2025 review did not confirm a different effect by starting level.[4]

Sources (11)

  1. Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.gov
  2. Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysis. Massé O, Mercurio CM, Dupuis S, Al Sahwi M, Arruda A, Dallaire G, et al. BMJ, 2026. PMID 42161415
  3. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S, et al. N Engl J Med, 2019. PMID 30415629
  4. 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
  5. Vitamin D supplementation for term breastfed infants to prevent vitamin D deficiency and improve bone health. Tan ML, Abrams SA, Osborn DA Cochrane Database Syst Rev, 2020. PMID 33305822
  6. 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
  7. 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
  8. Vitamin D and marine omega 3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial. Hahn J, Cook NR, Alexander EK, Friedman S, Walter J, Bubes V, et al. BMJ, 2022. PMID 35082139
  9. Vitamin and Mineral Supplements for the Primary Prevention of Cardiovascular Disease and Cancer: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force. O'Connor EA, Evans CV, Ivlev I, Rushkin MC, Thomas RG, Martin A, et al. JAMA, 2022. PMID 35727272
  10. The effect of vitamin D supplementation on depression: a systematic review and dose-response meta-analysis of randomized controlled trials. Ghaemi S, Zeraattalab-Motlagh S, Jayedi A, Shab-Bidar S Psychol Med, 2024. PMID 39552387
  11. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. LeBoff MS, Chou SH, Ratliff KA, Cook NR, Khurana B, Kim E, et al. N Engl J Med, 2022. PMID 35939577

More about vitamin d

What is vitamin D?How do you get vitamin D from sunlight and food?What vitamin D blood level is too low?Is vitamin D safe?Does vitamin D prevent fractures?Does vitamin D prevent colds and other respiratory infections?

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