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Vitamin D
A vitamin the skin makes in sunlight and a few foods contain. Many adults take it, and a 2026 review says it has been widely recommended to prevent fractures.
Explained simply · Last reviewed
What it is
Vitamin D is a vitamin that the skin makes when sunlight strikes it. The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, describes it as naturally present in a few foods, added to others, and sold as a dietary supplement. It reports that in 2015–2016, 28% of people in the United States aged 2 and older took a supplement containing vitamin D. The share rose with age, to 49% of men and 59% of women aged 60 and older.
More about Vitamin D
The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, describes it as naturally present in a few foods, added to others, and sold as a dietary supplement. It reports that in 2015–2016, 28% of people in the United States aged 2 and older took a supplement containing vitamin D. The share rose with age, to 49% of men and 59% of women aged 60 and older.
ODS says the body has to convert vitamin D twice before it is active: first in the liver, then mostly in the kidneys. It says vitamin D helps the gut absorb calcium and keeps blood calcium and phosphate at the levels bone needs to mineralise normally. Without enough, it says, bones can become thin, brittle or misshapen. It names rickets in children and osteomalacia in adults as what deficiency can lead to.
A 2026 review of calcium and vitamin D trials states that vitamin D, with or without calcium, has been widely recommended to prevent fractures and falls. It reports a substantial increase in calcium and vitamin D prescriptions in many countries. The claims below report what that review and others found.
Also known as: vitamin D3, cholecalciferol, vitamin D2, ergocalciferol, calciferol
At a glance
Safety: known risks, 2 groups who should avoid it or take extra care and 4 documented interactions. See Safety ↓Claims made about Vitamin D, and how strong the evidence is for each:
- Prevents fractures in adultsEvidence rating: Evidence against
- Prevents rickets and osteomalacia caused by deficiencyEvidence rating: Strong
- Lowers the risk of pre-eclampsia in pregnancyEvidence rating: Limited
Longevity and aging claims
Claims made about Vitamin D and aging, and how strong the evidence is for each. A change in a marker is not the same as a longer life.
- Lowers the risk of death from any cause in adultsEvidence rating: Limited
- Slows telomere shortening in white blood cellsEvidence rating: Limited
Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate
Safety
Read this before the ratings below.
Risks
- Vitamin D toxicity is almost always caused by supplements, not by food or sunlight. It raises blood calcium, which can cause nausea, vomiting, muscle weakness, loss of appetite, dehydration, excessive thirst, frequent urination, pain, neuropsychiatric disturbances, and kidney stones.
- In extreme cases the cited authority reports kidney failure, calcification of soft tissue including coronary vessels and heart valves, cardiac arrhythmias, and death.
- Taking calcium supplements alongside vitamin D may increase the risk of certain adverse effects. In one trial of 36,282 postmenopausal women, high calcium intake combined with moderate vitamin D raised the risk of kidney stones by 17% over 7 years.
- The cited authority notes that toxicity has resulted from manufacturing errors in supplements, from products taken inappropriately or in excessive amounts, and from incorrect prescribing.
Who should avoid it or take extra care
- People with kidney disease or impaired kidney function: vitamin D raises calcium absorption, and the authority flags compromised renal function as a setting where excess calcium becomes dangerous.
- Anyone taking the medications listed below on a regular basis should talk to their doctor or pharmacist about vitamin D.
Documented interactions
- Orlistat (Xenical, alli): Taken with a reduced-fat diet, orlistat can reduce how much vitamin D you absorb from both food and supplements, lowering blood levels. Source [1]
- Statins (for example atorvastatin/Lipitor, simvastatin/Zocor): Statins may reduce the body’s own vitamin D synthesis. High intakes of vitamin D, especially from supplements, might also reduce the potency of some statins, because they appear to compete for the same metabolizing enzyme. Source [1]
- Corticosteroids (for example prednisone): These can reduce calcium absorption and impair vitamin D metabolism. In one national survey, vitamin D deficiency was more than twice as common among people reporting oral steroid use. Source [1]
- Thiazide diuretics: These reduce how much calcium you lose in urine. Combined with vitamin D supplements, which increase calcium absorption, that may lead to high blood calcium — particularly in older adults and people with impaired kidney function or hyperparathyroidism. Source [1]
Safety sources: Source [1]
What the evidence says
Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.
Prevents fractures in adults Evidence rating: Evidence against
People take it hoping it will keep their bones strong and help them avoid fractures.
A 2026 review of 69 trials, mostly in adults not at high risk of fracture, found vitamin D on its own had little to no effect on the risk of any fracture, and rated that high certainty.
A 2026 systematic review pooled 69 trials covering 153,902 participants. For vitamin D on its own, it found little to no effect on the risk of any fracture. The risk ratio was 1.00, with a confidence interval running from 0.95 to 1.06, across 36 trials and 92,045 participants. The reviewers rated that finding high certainty. Combined calcium and vitamin D came out at 0.91, also high certainty, which the reviewers judged too small to be clinically meaningful.
Most trials were in people living in the community and not at high risk of fracture. The reviewers note that evidence for people at high risk or in residential care was limited for many outcomes of calcium alone and of calcium combined with vitamin D. So this page applies the finding to supplement use in the general adult population, not to people with a diagnosed deficiency or osteoporosis.
Sources: Source [1]
Prevents rickets and osteomalacia caused by deficiency Evidence rating: Strong
People take it to make sure they get enough vitamin D for healthy bones.
ODS, part of the US National Institutes of Health, states that vitamin D deficiency can lead to rickets in infants and children and osteomalacia in adults.
This claim rests on the Office of Dietary Supplements (ODS) at the US National Institutes of Health. It states that vitamin D sufficiency prevents rickets in children and osteomalacia in adults. It says that without enough vitamin D, bones can become thin, brittle or misshapen. It reports that the recommended intakes were set to maintain bone health and normal calcium metabolism.
Note what this claim covers: the bone disease that deficiency causes. It is not a claim that extra vitamin D helps someone who already has enough.
Sources: Source [1]
Lowers the risk of pre-eclampsia in pregnancy Evidence rating: Limited
Some people take it during pregnancy hoping it will lower the risk of pre-eclampsia.
A 2024 Cochrane review found the evidence very uncertain; a 2026 review in high-risk pregnancies linked higher-dose regimens to lower estimated risk, at low certainty.
A 2024 Cochrane review describes pre-eclampsia as new high blood pressure with protein in the urine after 20 weeks of pregnancy. It compared vitamin D on its own with placebo or no supplement, in pregnant women without pre-existing conditions. Only one of its trials reported pre-eclampsia, in 165 women (risk ratio 0.53, 95% confidence interval 0.21 to 1.33). The reviewers rate that very low certainty and call the evidence very uncertain.
The Cochrane reviewers screened every trial for trustworthiness. They set aside 20 trials that their 2019 version had included, mostly over governance, such as trials not registered in advance, and feasibility. They also excluded one retracted trial. The 2019 version had concluded that vitamin D alone probably reduces the risk of pre-eclampsia. The reviewers say their results are now very different, and call for larger, rigorous trials. They suggest that other reviews reporting benefits could differ because they included trials with a lower-dose control group and did not exclude trials on quality. One Cochrane author's listed affiliation is Daiichi Sankyo, a drug company. The review's declarations of interest state none known for that author.
A 2026 network meta-analysis, which compares several treatments at once, looked only at high-risk pregnancies. It searched the five years to September 2025 and pooled 8 randomized trials in 4,078 women. Each trial defined high risk its own way, for example prior pre-eclampsia, obesity, metabolic conditions or vitamin D deficiency. The authors report that higher vitamin D doses were linked to a lower estimated risk of pre-eclampsia. Against placebo, that rested on a single trial (risk ratio 0.36, 0.19 to 0.70). Against a lower dose, it rested on four trials, three of them at high risk of bias.
The network meta-analysis authors judge the certainty low, and low to very low for most outcomes, from an informal appraisal rather than a formal grading. They say the effect sizes should not be read as evidence of clinical effectiveness. They call the findings hypothesis-generating, meant to inform future studies rather than guide clinical practice. This page rates the claim on the Cochrane review's very low certainty, the lower of the two.
Sources: Source [1]Source [2]
Longevity and aging
What the cited sources report about lifespan, death from any cause, and markers studied in connection with aging. A change in a marker is not the same as a longer life. Each outcome is rated on its own evidence, on the same scale as the claims above.
Lowers the risk of death from any cause in adults Evidence rating: Limited
People take it hoping it will help them live longer.
A 2014 Cochrane review and a 2023 review found a slightly lower risk of death with vitamin D, Cochrane rating its D3 result moderate quality; a 2019 review found no link and rated that high quality.
Reviews of randomized trials in adults disagree on this: two report a small reduction in deaths and one reports none. A 2014 Cochrane review, which searched for trials up to 2012, found slightly fewer deaths across 56 trials with 95,286 participants (risk ratio 0.97, 95% confidence interval 0.94 to 0.99). Most of its trials enrolled women older than 70. Analyzed by form, it found lower mortality only with vitamin D3 (risk ratio 0.94, 0.91 to 0.98; 38 trials, 75,927 participants). It rated that moderate-quality evidence, downgraded for risk of attrition bias. Vitamin D2, alfacalcidol and calcitriol did not significantly affect mortality.
The Cochrane authors report that more than 8% of participants dropped out. Best-case and worst-case analyses of those missing participants showed vitamin D could be associated with a dramatic increase or decrease in mortality. They called for further placebo-controlled trials. A 2019 meta-analysis in the BMJ pooled 50 trials with 74,655 participants. It found that vitamin D supplementation alone was not associated with death from any cause (risk ratio 0.98, 0.95 to 1.02), which it rated high quality using GRADE. It found lower mortality in trials of vitamin D3 than in trials of vitamin D2 (P for interaction 0.04). But neither form on its own significantly reduced death from any cause.
The BMJ authors conclude that "Additional large clinical studies are needed to determine whether vitamin D3 supplementation is associated with lower all cause mortality". They attribute the difference from earlier reviews to different selection criteria and newer trials. They excluded trials that combined vitamin D with calcium, trials of vitamin D analogs and one retracted trial, and included 17 trials published after 2014. Adding the excluded trials back did not change their result.
A 2023 meta-analysis of 80 trials in Nutrients found lower odds of death from any cause (odds ratio 0.95). The abstract gives its 95% confidence interval as 0.91 to 0.99, the results section as 0.93 to 0.99. The result held when its good- and fair-quality trials were pooled (odds ratio 0.95, 0.91 to 0.99). It was borderline when each of those groups was analyzed on its own. Its authors conclude that vitamin D "appears to decrease the risk of ACM (especially convincing in the fair- and good-quality RCTs)". The BMJ and Cochrane reviews also report fewer cancer deaths with vitamin D; in the BMJ review, all of those trials used D3. A published correction to the BMJ review changed its cancer-death estimate slightly; the correction states that it does not change the article’s results or interpretation. Cancer deaths are not rated here.
Sources: Source [1]Source [2]Source [3]
Slows telomere shortening in white blood cells Evidence rating: Limited
People take it hoping it will slow the aging of their cells.
One US trial found less telomere shortening over four years with vitamin D3, in a post hoc analysis; in 777 Swiss adults, vitamin D alone was not associated with changes in DNA-methylation clocks.
Telomeres are the protective ends of chromosomes. The VITAL study authors describe telomere length in white blood cells as a proposed biomarker of premature aging of the immune system. This entry is about that marker: no study cited here measured lifespan or death. In the US VITAL trial, a sub-study of 1,031 participants (women aged 55 and over, men aged 50 and over) found that telomeres shortened less over four years with vitamin D3 than with placebo. The difference was 0.14 kilobase pairs (95% confidence interval 0.007 to 0.27).
The VITAL authors describe it as a post hoc analysis of a trial that was not originally designed to test this. They call for independent large trials to replicate it. It is a single trial, so this page rates the evidence as limited.
A different marker gave a null result. In DO-HEALTH, 777 Swiss adults aged 70 and over were followed for three years. Vitamin D on its own was not associated with changes in any of the DNA-methylation clocks measured, which the authors describe as clocks of biological aging. For one of them, PhenoAge, the authors report additive benefits when omega-3 was combined with vitamin D, with a home exercise program, or with both. They state that the significance of the clock changes for long-term survival is unknown.
DO-HEALTH was funded in part by companies including Roche, Pfizer and NESTEC. One of its authors works for Altos Labs, a biotechnology company, and founded a nonprofit foundation that has licensed patents for epigenetic clocks, including GrimAge.
Sources: Source [1]Source [2]
How and when to take it
What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.
The upper limit for adults is 100 mcg (4,000 IU) a day
The cited authority sets the Tolerable Upper Intake Level at 100 mcg (4,000 IU) for everyone aged 9 and over, including during pregnancy and lactation. It describes this as the maximum daily intake unlikely to cause adverse effects. Source [1]
ODS says experts do not believe excessive sun exposure causes vitamin D toxicity, but that frequent tanning-bed use can raise blood levels
The cited authority says experts do not believe excessive sun exposure causes vitamin D toxicity, because the skin limits how much forms. It notes that frequent tanning-bed use can raise blood levels well above the range it associates with potential harm. Source [1]
Taking it with calcium changes the risk picture
The cited authority reports that taking calcium supplements together with vitamin D may increase the risk of certain adverse effects, and describes a trial in which high calcium intake alongside moderate vitamin D raised the risk of kidney stones. Source [1]
Reference intake values
Quoted exactly as published by the cited authority. These are population reference values, not a recommendation for you. Ask your doctor or pharmacist what applies to your situation.
Adults, 19–50 years
- Recommended intake
- 15 mcg (600 IU)
- Upper limit
- 100 mcg (4,000 IU)
- Source
- Source [1]
Adults, 51–70 years
- Recommended intake
- 15 mcg (600 IU)
- Upper limit
- 100 mcg (4,000 IU)
- Source
- Source [1]
Adults, 71+ years
- Recommended intake
- 20 mcg (800 IU)
- Upper limit
- 100 mcg (4,000 IU)
- Source
- Source [1]
Pregnancy and lactation, 19–50 years
- Recommended intake
- 15 mcg (600 IU)
- Upper limit
- 100 mcg (4,000 IU)
- Source
- Source [1]
Sources
- Calcium, vitamin D, or combined supplementation to prevent fractures and falls: systematic review and meta-analysisBMJ, 2026 · Meta-analysis · Primary source · Certainty: high
- Vitamin D: Fact Sheet for Health ProfessionalsNIH Office of Dietary Supplements, 2026 · Health authority summary · Primary source
- Vitamin D supplementation for women during pregnancyCochrane Database of Systematic Reviews, 2024 · Systematic review · Primary source · Certainty: very low
- Comparative effectiveness of statins, metformin, and vitamin D, for prevention of preeclampsia: a systematic review and network meta-analysis of randomized trialsBMC Pregnancy and Childbirth, 2026 · Meta-analysis · Primary source
- Vitamin D supplementation for prevention of mortality in adultsCochrane Database of Systematic Reviews, 2014 · Systematic review · Primary source · Certainty: low
- Association between vitamin D supplementation and mortality: systematic review and meta-analysisBMJ, 2019 · Meta-analysis · Primary source · Certainty: high
- Vitamin D Supplementation and Its Impact on Mortality and Cardiovascular Outcomes: Systematic Review and Meta-Analysis of 80 Randomized Clinical TrialsNutrients, 2023 · Meta-analysis · Primary source
- Vitamin D3 and marine ω-3 fatty acids supplementation and leukocyte telomere length: 4-year findings from the VITamin D and OmegA-3 TriaL (VITAL) randomized controlled trialThe American Journal of Clinical Nutrition, 2025 · Randomized controlled trial · Supporting source
- Individual and additive effects of vitamin D, omega-3 and exercise on DNA methylation clocks of biological aging in older adults from the DO-HEALTH trialNature Aging, 2025 · Randomized controlled trial · Supporting source
Page history
Show all 4 changes to this page
- — Added pre-eclampsia in pregnancy, rated limited on very low-certainty evidence. A 2024 Cochrane review found the evidence very uncertain; a 2026 review in high-risk pregnancies linked higher-dose regimens to lower estimated risk, rating its own evidence low certainty. No existing claim, rating or source changed.
- — Rewritten to the content style guideline; ratings and sources unchanged.
- — Added a longevity section. Death from any cause in adults rated limited, where two reviews report a small reduction and one reports none; telomere shortening in white blood cells rated limited on a single trial.
- — First published. Deficiency-related bone disease rated strong, fracture prevention in the general adult population rated evidence-against.