A fat-soluble vitamin that the skin makes in sunlight and a few foods contain. Most studied for bones, fractures and respiratory infections.
Ask a doctor or pharmacist first if you:
Vitamin D is a fat-soluble vitamin. The skin makes it when UVB rays from the sun reach it, and a few foods such as fatty fish and egg yolks contain it.[1]
Supplements contain vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol). D2 is made from yeast, D3 from sheep's wool fat or, for a vegan form, from lichen.[1] The body needs vitamin D to absorb calcium and to build bone.[1]
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.[3][4] Its effect on respiratory infections was small or none.[5]
In VITAL, 2000 IU a day for a median of 5.3 years caused no more cases of high blood calcium or other side effects than a placebo.[4] The upper limit for adults is 4000 IU (100 µg) a day in the US and in the EU.[1][6]
Too much vitamin D over time raises blood calcium. This can cause nausea, vomiting, muscle weakness and kidney stones.[1] Ask a doctor or pharmacist first if you take a thiazide diuretic, a statin, a corticosteroid or orlistat.[1] More: What happens if you take too much vitamin D?
Vitamin D from sunlight, food or a supplement is not active at first. The liver and then the kidneys change it into its active form, which helps the gut absorb calcium for bone.[1]
UVB rays from the sun turn a compound in the skin into vitamin D3. Vitamin D from food and supplements is absorbed in the small intestine, better when the meal has some fat.[1]
The liver changes vitamin D into 25-hydroxyvitamin D, written 25(OH)D. This is the form a blood test measures. Its half-life in the blood is about 15 days.[1]
The kidneys change 25(OH)D into calcitriol, the active form. Parathyroid hormone, calcium and phosphate keep the calcitriol level in a narrow range.[1]
Calcitriol helps the gut absorb calcium and keeps blood calcium and phosphate high enough to build bone. With too little vitamin D, bones become soft: rickets in children, osteomalacia in adults.[1]
Body fat holds on to vitamin D. People with obesity have lower blood levels and may need more vitamin D to reach the same level.[1]
Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.
No benefit matches the filter. Clear it to see all 19.
In large trials, the daily dose was 400 to 800 IU (10 to 20 µg) of vitamin D with calcium, or 2000 IU (50 µg) of vitamin D3 without calcium.[7][4] The US recommended intake for adults is 600 IU (15 µg) a day, and 800 IU (20 µg) after age 70.[1]
With a meal that contains fat. In one trial, a dose of vitamin D3 taken with a fat-containing meal gave a 32% higher peak blood level than with a fat-free meal.[10]
Most studies gave 500 to 1,000 IU a day, for 1 to 3 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
872 of 2518 study groups took vitamin D with something else. This shows what studies gave together, not what works together.
What studies used when they gave vitamin D for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Most people get some vitamin D from the sun: UVB rays make it in uncovered skin.[1] Season, time of day, clouds, dark skin, older age and sunscreen lower the amount. Window glass blocks UVB, so sun through a window makes no vitamin D.[1]
Few foods contain much. A tablespoon of cod liver oil has 1360 IU, 3 ounces (85 g) of cooked sockeye salmon 570 IU, and one egg 44 IU.[1] In the US, fortified milk, plant milks and cereals give most of the vitamin D in the diet. A cup of fortified milk has about 120 IU.[1]
A blood test measures 25(OH)D. US experts consider 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] Above 125 nmol/L (50 ng/mL), side effects become possible.[1]
Low levels are more common in breastfed babies, older adults, people with dark skin or little sun, and people with obesity.[1] Gut conditions that limit fat absorption, such as Crohn's disease or celiac disease, and gastric bypass surgery also lower it.[1] Results differ between laboratories, because the tests are not fully standardized.[1]
Vitamin D alone does not. A 2026 review of 36 trials with 92,045 adults found no change in the risk of a fracture.[3] Taken with calcium, it lowered the risk by 9% in 15 trials, which the authors judged to be little to no benefit.[3]
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.[5] Age, the starting blood level, the dose and how often people took it did not change the result.[5]
The trials disagree. A 2024 review of 31 trials with 24,189 adults found that each 1000 IU a day lowered depression scores a little. The effect was larger in people with depressive symptoms and in trials of 24 weeks or less.[11]
Trials longer than a year found no effect.[11] In VITAL, 2000 IU a day for a median of 5.3 years did not prevent depression in adults aged 50 or older.[1] More on the stress and mood page.[11]
Large trials say no. In VITAL, 25,871 US adults took 2000 IU of vitamin D3 a day or a placebo for a median of 5.3 years. Cancer and major heart events were as common in both groups.[4]
A 2022 review for the US Preventive Services Task Force found no effect on heart disease in 7 trials or on cancer in 19 trials.[12] Three reviews of trials found 12% to 13% fewer deaths from cancer, though not fewer cancers.[1] More on the heart health page.[4]
Too much vitamin D raises the calcium in the blood. This can cause nausea, vomiting, muscle weakness, pain, loss of appetite, thirst, frequent urination and kidney stones.[1] It almost always comes from supplements, not from the sun.[1] The adult upper limit is 4000 IU (100 µg) a day.[1][6]
Yes, with a few. Thiazide diuretics together with vitamin D can raise blood calcium too high, mostly in older adults and people with kidney problems.[1] High doses of vitamin D may make atorvastatin, lovastatin and simvastatin work less well.[1]
Corticosteroids such as prednisone reduce calcium absorption and change how the body uses vitamin D. The weight-loss drug orlistat lowers vitamin D absorption.[1] If you take any of these, ask a doctor or pharmacist about your vitamin D intake.[1]
It is not clear. A 2024 Cochrane review set aside 20 earlier trials after a check of their trustworthiness, and now includes 10. For pre-eclampsia, gestational diabetes and preterm birth, the evidence was very uncertain.[13] Vitamin D may lower the risk of severe bleeding after birth, but only one trial measured it. It may also lower the risk of low birthweight, but a higher risk could not be ruled out. Both results were of low certainty.[13]
The US recommended intake in pregnancy is 600 IU (15 µg) a day, and the upper limit is 4000 IU (100 µg).[1]
For raising the blood level, yes. In a 2024 review, in 12 comparisons of daily doses, vitamin D2 raised total 25(OH)D by about 10 nmol/L, or 40%, less than vitamin D3.[9] Both forms are well absorbed, and they seem to cure rickets equally well.[1]
Taking it with a meal that contains fat helps. In a trial of 50 healthy older adults, a single 50,000 IU dose of vitamin D3 was taken with breakfast.[10] With a fat-containing breakfast, the peak blood level of vitamin D3 was 32% higher than with a fat-free one.[10]
The ratio of monounsaturated to polyunsaturated fat in the meal did not matter.[10] Some vitamin D is absorbed even without fat in the meal.[1]
Daily or weekly doses have the better record. In a 2017 analysis of 25 trials, daily or weekly vitamin D lowered the odds of respiratory infections by 19%. Large single (bolus) doses did not lower them.[14]
In older women, one dose of 500,000 IU a year raised falls by 15% and fractures by 26%.[2] A 2025 review of respiratory infections found no difference between daily and less frequent doses.[5]
