Vitamins

Vitamin D3

Also known as: Cholecalciferol, Vitamin D, The sunshine vitamin

A fat-soluble vitamin made in skin from sunlight, widely supplemented for bone, muscle, and immune health.

By IngredientWiki Editorial Team
Fact-checked by IngredientWiki Editorial Team
Updated 2026-09-25
3 min read

In short

Vitamin D3 (cholecalciferol) is a fat-soluble vitamin that your skin produces when exposed to sunlight and that you can also get from supplements and a few foods. It helps the body absorb calcium and phosphorus for healthy bones, supports muscle and immune function, and is one of the most commonly deficient nutrients in the United States.

Produced in skin from UVB sunlight; also in fatty fish, egg yolks, and fortified foods
Enables calcium and phosphorus absorption for bone health
Recommended intake for adults is 600–800 IU (15–20 mcg) per day
Upper limit for adults is 4,000 IU (100 mcg) per day

What is Vitamin D3?

Vitamin D is a fat-soluble vitamin that acts more like a hormone than a classic vitamin. Your body makes it in the skin when UVB rays from sunlight hit a cholesterol-derived precursor. Vitamin D3 (cholecalciferol) is the form your skin makes and the form found in most supplements; it is considered slightly more effective at raising blood levels than vitamin D2 (ergocalciferol). Because few foods naturally contain meaningful amounts, and because modern lifestyles keep people indoors, supplements are a primary source of vitamin D for many Americans.

Where it comes from

Natural sources

Skin synthesis from UVB sunlight exposure
Fatty fish such as salmon, mackerel, and sardines
Egg yolks, beef liver, and UV-exposed mushrooms
Fortified foods such as milk, orange juice, and cereals

How it's made

Supplemental cholecalciferol is typically produced from lanolin (sheep's wool) or, for vegan products, from lichen.

What it does in products

Benefits

Bone health and calcium absorption

strong evidence

Vitamin D3 enables the gut to absorb calcium and phosphorus. Without enough vitamin D, bones can become thin and brittle. Correcting deficiency reduces the risk of rickets in children and osteomalacia and osteoporosis-related fractures in adults.

Correcting deficiency

strong evidence

Deficiency is common, especially in winter, at northern latitudes, and in people with darker skin, limited sun exposure, or obesity. Blood levels below 20 ng/mL are considered deficient by most guidelines; supplementation reliably raises levels.

Immune function

moderate evidence

Immune cells carry vitamin D receptors. Observational studies link low vitamin D status with higher rates of respiratory infections, but large trials show supplementation mainly helps people who are already deficient.

Muscle strength and fall prevention

moderate evidence

Vitamin D supports muscle function, and trials in older adults suggest that supplementation, particularly in those with low levels, may reduce falls and improve strength.

Side effects & safety

Generally well tolerated at recommended doses (rare)Most people notice no side effects at 600–2,000 IU per day.

Hypercalcemia at very high doses (rare)Sustained intake above the 4,000 IU upper limit can raise blood calcium, causing nausea, weakness, and kidney stones. Toxicity is almost always from excessive supplementation, never from sun exposure.

Safety considerations

The pregnancy RDA is 600 IU per day. Doses above the upper limit should only be used under medical supervision.
Thiazide diuretics can increase calcium levels; combining with high-dose vitamin D requires monitoring.
Certain weight-loss drugs (orlistat) and bile acid sequestrants can reduce fat-soluble vitamin absorption.
Not for: High blood calcium (hypercalcemia) or conditions that predispose to it, such as sarcoidosis

How it's used

In supplements

Adults up to age 70: 600 IU (15 mcg) daily; over 70: 800 IU (20 mcg). Higher doses (1,000–4,000 IU) are often used to correct deficiency, ideally guided by a blood test. Vitamin D is fat-soluble and is better absorbed with a meal containing fat.

Regulatory status

Dietary supplements are regulated by the FDA under DSHEA; vitamin D3 supplements do not require pre-market approval, but manufacturers must ensure safety and accurate labeling.
GRAS (generally recognized as safe) for food use.

Vitamin D2 vs vitamin D3

Vitamin D comes in two main forms. Vitamin D2 (ergocalciferol) comes from fungi and yeast and is used in some vegan supplements and fortified foods. Vitamin D3 (cholecalciferol) is the form your skin makes and the form found in animal sources. Both raise blood levels, but research consistently shows that D3 raises and maintains blood vitamin D levels more effectively than D2 at equal doses, which is why D3 dominates the US supplement market.

Comparing the two forms of vitamin D
	Vitamin D2 (ergocalciferol)	Vitamin D3 (cholecalciferol)
Source	Fungi, yeast, fortified foods	Skin synthesis, animal foods, lanolin
Common in supplements	Vegan products	Most US supplements
Effect on blood levels	Raises levels	Raises and maintains levels more effectively

Frequently asked questions

How much vitamin D3 should I take daily?

The Recommended Dietary Allowance (RDA) for adults is 600 IU (15 mcg) per day up to age 70 and 800 IU (20 mcg) over 70. Many doctors suggest 1,000–2,000 IU daily for maintenance, especially in winter. A blood test is the best way to personalize dosing.

Can I get enough vitamin D from the sun alone?

It depends on skin type, latitude, season, sunscreen use, and time spent outdoors. In much of the US, winter UVB levels are too low for skin synthesis north of roughly 37 degrees latitude. Diet and supplements are often needed to maintain levels.

When is the best time to take vitamin D3?

Vitamin D is fat-soluble, so it is best absorbed with a meal that contains some fat. Time of day matters little for absorption; some people report better sleep when taking it in the morning, but the evidence is anecdotal.

The bottom line

Vitamin D3 is a well-studied, safe, and inexpensive supplement. The strongest evidence supports using it to prevent or correct deficiency, which in turn protects bone health. Doses within the RDA to upper-limit range are safe for most adults; a blood test is the most reliable way to know whether you need it.

References

Vitamin D — Health Professional Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
Vitamin D — Consumer Fact Sheet. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
Cholecalciferol compound summary. PubChem (National Library of Medicine). https://pubchem.ncbi.nlm.nih.gov/compound/5280795
Vitamin D deficiency in adults: Definition, clinical manifestations, and treatment. UpToDate. https://www.uptodate.com/contents/vitamin-d-deficiency-in-adults-definition-clinical-manifestations-and-treatment