What Ingredients Does Vitamin D Have? Understanding the Two Key Forms

December 5, 2025 •

2 min read

Vitamin D isn't a single ingredient but a group of fat-soluble compounds called secosteroids, with over 1 billion people worldwide having inadequate levels. The term commonly refers to two distinct forms, vitamin D2 and vitamin D3, which originate from different sources but serve the same essential function in the body after a series of conversions.

Quick Summary

Vitamin D is a family of fat-soluble secosteroids, primarily found in two forms: D2 (ergocalciferol) from plants and D3 (cholecalciferol) from animal sources or sunlight. Supplements contain either D2 or D3 and are converted to the active hormone, calcitriol, in the body for calcium absorption and immune support.

Key Points

Two Primary Forms: The term vitamin D refers mainly to two types, D2 (ergocalciferol) and D3 (cholecalciferol), both of which are fat-soluble secosteroids.
D3 (Cholecalciferol) Source: Vitamin D3 is made in human and animal skin from a cholesterol precursor (7-dehydrocholesterol) upon exposure to UVB sunlight, or can be obtained from animal products.
D2 (Ergocalciferol) Source: Vitamin D2 originates from plants and fungi, synthesized by irradiating ergosterol, and is commonly used to fortify foods and in plant-based supplements.
Biological Potency Differences: Research suggests that vitamin D3 is more effective than D2 at raising and sustaining blood vitamin D levels, though both are beneficial.
Supplements Vary: Vitamin D supplements can contain either D2 (from yeast) or D3 (from lanolin or lichen), and the source should be checked, especially by vegans.

Vitamin D: More Than a Single Compound

Chemically, vitamin D is a group of fat-soluble secosteroids responsible for increasing the intestinal absorption of important minerals like calcium and phosphate. Rather than having a list of ingredients, it is a complex organic molecule that exists in several forms, known as vitamers. The two most significant for human nutrition are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While their initial sources differ greatly, both are inactive precursors that the body must convert into the active hormone, calcitriol, in a two-step process involving the liver and kidneys.

Vitamin D3 (Cholecalciferol): The Animal-Sourced 'Sunshine' Vitamin

Cholecalciferol, or vitamin D3, is the form produced in the skin of humans and many animals when exposed to ultraviolet B (UVB) radiation from sunlight. This process converts a cholesterol precursor into previtamin D3, which then becomes vitamin D3.

Natural food sources rich in vitamin D3 include:

Fatty fish such as salmon and tuna.
Fish liver oils.
Egg yolks.
Beef liver.

Dietary supplements often contain vitamin D3 manufactured by irradiating a substance from sheep's wool (lanolin) or, for animal-free versions, from lichen.

Vitamin D2 (Ergocalciferol): The Plant-Based Form

Ergocalciferol, or vitamin D2, is the form found in plant sources and fungi like mushrooms and yeast. It is created when the sterol ergosterol is exposed to ultraviolet light.

Sources of vitamin D2 include:

Mushrooms exposed to UV light.
Fortified foods, such as certain cereals and plant-based milks.
Supplements, manufactured by irradiating ergosterol from yeast.

How Supplements are Made

Vitamin D2 and D3 are produced for supplements by exposing their precursors to ultraviolet radiation. D3 is often sourced from lanolin or lichen, while D2 is sourced from yeast. Both forms are absorbed in the small intestine, with absorption improved when consumed with fat.

Comparison of Vitamin D2 (Ergocalciferol) and Vitamin D3 (Cholecalciferol)


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Source	Plants, fungi (e.g., mushrooms)	Animals (fatty fish, egg yolks) and human skin via sunlight
Precursor	Ergosterol	7-Dehydrocholesterol
Primary Production	UV irradiation of yeast	UV irradiation of lanolin from sheep's wool or lichen
Biological Potency	Slightly less potent, and studies suggest it may raise blood vitamin D levels less effectively and for a shorter duration.	Considered more potent and more effective at raising and maintaining blood vitamin D levels over time.
Vegan Friendly	Yes, derived from plant sources.	Can be sourced from lichen, making it available for vegans.
Fortified Foods	Often used in fortified plant-based milk alternatives and cereals.	Often used in fortified cow's milk.

Conclusion

Vitamin D is a family of secosteroids, primarily D2 and D3, rather than a single ingredient. Vitamin D3 comes from sun exposure and animal products and is generally considered more potent for raising blood levels. Vitamin D2 is plant and fungi-based and is a suitable alternative, especially for those on plant-based diets. Both forms are crucial for maintaining adequate vitamin D levels and support essential bodily functions.

Learn more about Vitamin D from the NIH Office of Dietary Supplements

Frequently Asked Questions

The chemical name for vitamin D2 is ergocalciferol, and the chemical name for vitamin D3 is cholecalciferol.

Yes, studies suggest that vitamin D3 is slightly more potent and effective at raising and maintaining blood vitamin D levels for a longer period than vitamin D2.

Supplement manufacturers typically produce vitamin D3 by irradiating 7-dehydrocholesterol obtained from lanolin, a wax from sheep's wool. Vegan D3 is sourced from lichen.

Vitamin D2 for supplements is manufactured by exposing ergosterol from yeast to ultraviolet (UV) radiation.

Few foods naturally contain significant vitamin D. The best natural sources include fatty fish (like salmon and tuna), fish liver oils, egg yolks, and beef liver.

Vitamin D is a secosteroid, meaning it is a steroid molecule with a broken ring, unlike a simple single ingredient. It is a precursor that the body converts into an active hormone, calcitriol, after a series of metabolic steps.

Vitamin D3 is made in the skin when UVB light from the sun converts a cholesterol derivative, 7-dehydrocholesterol, into previtamin D3, which then becomes cholecalciferol.