Vitamin D Supplements: How Much You Need and How to Choose

Vitamin D helps your body absorb calcium and keep bones strong, and it plays roles in muscles, nerves and the immune system. Your skin makes it from sunlight, but in winter, at northern latitudes, with darker skin or if you spend most of your time indoors, you may not make enough. Few foods contain much vitamin D naturally.

Vitamin D is one of the most popular supplements in the US, and also one of the most overhyped. This guide explains how much you need, who benefits from a supplement, D3 versus D2, what big trials have found, the risks of taking too much, and how to choose a product. For more buying guides, see our supplement guides, or browse our vitamin and mineral guides.

How much vitamin D you need

US recommendations from the National Academies assume minimal sun exposure, so they’re meant to be covered by food and supplements.

Source: NIH Office of Dietary Supplements. The Daily Value used on supplement labels is 20 mcg (800 IU).

Labels now list vitamin D in micrograms, often with IU in brackets. To convert, multiply mcg by 40: 25 mcg is 1,000 IU, and 50 mcg is 2,000 IU.

Who should consider a supplement?

US survey data suggest about 5 percent of Americans are at risk of vitamin D deficiency and about 18 percent have inadequate levels. You’re more likely to fall short if you:

• Get little sun, because you work indoors, cover your skin, live far from the equator or are housebound.
• Have darker skin, which makes less vitamin D from the same sun exposure.
• Are older, as the skin makes less vitamin D with age.
• Have obesity or have had weight-loss surgery.
• Have a condition that affects fat absorption, such as celiac disease, Crohn’s disease or cystic fibrosis.
• Eat a vegan diet or avoid dairy and fortified foods.
• Are a breastfed baby. Breast milk is low in vitamin D, so the American Academy of Pediatrics recommends 400 IU a day for breastfed and partly breastfed infants.

In 2024, the Endocrine Society suggested vitamin D above the standard recommendation for four groups: children and teenagers, adults aged 75 and older, pregnant people, and adults with high-risk prediabetes. It advised against extra vitamin D for healthy adults under 75 who aren’t at risk of deficiency.

Vitamin D from sun and food

Sunlight is the main natural source. Short periods of midday sun on bare arms and legs can produce a good amount of vitamin D in summer, but the amount varies enormously with season, latitude, skin color, age and sunscreen. Because of skin cancer risk, doctors don’t recommend relying on sun exposure for vitamin D.

Few foods are naturally rich in vitamin D, and in the US fortified foods provide most of it:

• Cod liver oil, 1 tablespoon: 34 mcg (1,360 IU)
• Farmed rainbow trout, 3 oz: 16 mcg (645 IU)
• Sockeye salmon, 3 oz: 14 mcg (570 IU)
• UV-exposed mushrooms, ½ cup: about 9 mcg (366 IU)
• Fortified milk, 1 cup: about 3 mcg (120 IU)
• Fortified plant milks, 1 cup: 2.5 to 3.6 mcg (100 to 144 IU)
• Egg yolk, 1 large egg: about 1 mcg (44 IU)

What the research shows

Vitamin D has been linked to dozens of health outcomes in observational studies, where people with low levels tend to have more disease. But large randomized trials, which test whether giving vitamin D changes outcomes, have mostly been disappointing for people who aren’t deficient. Each finding below carries an evidence label, explained in our editorial policy.

Preventing and treating deficiency Strong evidence

Supplements reliably raise vitamin D levels and prevent and treat rickets in children and osteomalacia (soft bones) in adults. This is the clearest benefit.

Bones and fractures Moderate evidence

Vitamin D combined with calcium can modestly reduce fracture risk in older people living in care homes, who are often deficient. In healthy adults living at home who aren’t deficient, vitamin D alone hasn’t been shown to prevent fractures.

Falls and muscle strength Limited evidence

Results are mixed. Some trials in older adults with low levels showed fewer falls, while very high intermittent doses, such as large monthly or yearly doses, have actually increased falls in some studies. This is one reason guidelines favor modest daily doses.

Respiratory infections Limited evidence

Some meta-analyses found daily vitamin D slightly reduced acute respiratory infections, especially in people with low levels and in children. The effect is small, and vitamin D doesn’t prevent or treat COVID-19.

Mood, diabetes and other conditions Limited evidence

In the general population, vitamin D supplements haven’t been shown to lower the risk of depression. In people with prediabetes, it may slightly lower the risk of developing type 2 diabetes, which is why the Endocrine Society suggests it for high-risk prediabetes.

D3 vs D2 and other forms

Supplements come in two main forms. Both are converted in the liver to 25-hydroxyvitamin D, the form doctors measure in blood tests.

• Vitamin D3 (cholecalciferol): the form your skin makes. Most evidence shows it raises blood levels more and keeps them up longer than D2. Usually made from lanolin (sheep’s wool), with vegan versions made from lichen.
• Vitamin D2 (ergocalciferol): made from yeast or mushrooms and suitable for vegans. Used in some prescription high-dose capsules. It works, but you may need a little more to reach the same level.
• Calcifediol and calcitriol: activated forms used as prescription medicines for specific conditions, such as kidney disease. They aren’t everyday supplements.

Vitamin D is also sold combined with vitamin K2, calcium or magnesium. These combinations are fine but not necessary for most people. If you take warfarin, avoid products with vitamin K unless your doctor agrees.

How much to take and how

• For most adults who want a supplement: 15 to 25 mcg (600 to 1,000 IU) a day covers the recommended intake, allowing for what you get from food.
• Over 70, or with risk factors: 20 to 50 mcg (800 to 2,000 IU) a day is commonly used.
• If you’re deficient: your doctor may prescribe a higher dose for a set period, then a lower maintenance dose. Don’t self-treat with very high doses.
• Daily is better than large occasional doses: the Endocrine Society favors daily, lower doses over weekly or monthly high doses for adults over 50.
• Count every source: multivitamins, calcium-plus-D products, fortified foods and cod liver oil all add up toward the 4,000 IU upper limit.

Vitamin D works with calcium and magnesium for bone health. Our guide to types of magnesium explains how to choose a magnesium supplement if you need one.

Too much vitamin D and interactions

Vitamin D toxicity is rare and almost always comes from taking too many supplements, not from sun or food. It causes high blood calcium, with symptoms such as nausea, vomiting, muscle weakness, confusion, loss of appetite, extreme thirst, frequent urination and kidney stones. Severe cases can cause kidney failure, an irregular heartbeat and, rarely, death. Cases have occurred when people took very high doses for months, or when products contained far more vitamin D than their labels said.

See also our medical disclaimer.

Should you get your level tested?

A blood test for 25-hydroxyvitamin D shows your vitamin D status. The NIH considers a level below 30 nmol/L (12 ng/mL) a risk of deficiency, and 50 nmol/L (20 ng/mL) or more adequate for most people. Levels above 125 nmol/L (50 ng/mL) have been linked to possible harm.

The 2024 Endocrine Society guideline suggests against routine testing for healthy people, including during pregnancy and for people with darker skin or obesity, because there’s no clear target level proven to prevent disease. Testing is still useful if you have symptoms of deficiency, a condition that affects absorption, osteoporosis, or are taking high doses. Ask your doctor whether testing makes sense for you.

How to choose a vitamin D supplement

• Choose vitamin D3 unless you need a vegan product, in which case lichen-derived D3 or D2 both work.
• Pick a sensible dose: 600 to 2,000 IU (15 to 50 mcg) suits most adults. A 5,000 or 10,000 IU daily product is more than most people need and exceeds the upper limit.
• Look for a USP Verified or NSF seal: testing has found vitamin D products with far more or less than the label claims. A seal confirms the dose is accurate.
• Check what else is in it: calcium, vitamin K or other additions may not suit you.
• Choose a format you’ll take daily: softgels, tablets, liquid drops and gummies all work. Drops are useful for infants and for flexible dosing; gummies may contain sugar.
• Compare cost per dose: vitamin D is one of the cheapest supplements, so there’s no need to pay a premium.

Our guide on how to read a supplement label explains mcg and IU, % Daily Value and quality seals in more detail.

Vitamin D FAQ