Uncovering the Truth: What Contains Vitamin D4?

December 20, 2025 •

3 min read

While most people are familiar with vitamins D2 and D3, many are unaware of the existence of vitamin D4. This lesser-known form of vitamin D is found almost exclusively in specific types of mushrooms, but what contains vitamin D4 and how significant is it for human health?

Quick Summary

Vitamin D4, also known as 22-dihydroergocalciferol, is a form of vitamin D produced naturally in fungi, particularly mushrooms exposed to UV light. Its physiological effects and bioavailability in humans are not as well-researched as D2 and D3.

Key Points

Source: Vitamin D4 is found almost exclusively in mushrooms, specifically those that have been exposed to UV light.
Chemical Name: It is also known as 22-dihydroergocalciferol and is derived from a different precursor than D2 or D3.
Limited Research: The effects of vitamin D4 on human health and its specific bioavailability are not well-established due to limited research.
UV Synthesis: The vitamin D4 content in mushrooms is created when UV radiation converts the fungal precursor, 22,23-dihydroergosterol.
Not a Common Supplement: Unlike D2 and D3, which are widely available in fortified foods and supplements, vitamin D4 is not typically used for human supplementation.

What Exactly is Vitamin D4?

Vitamin D is essential for several bodily functions, including calcium and phosphate absorption. While vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are well-known, vitamin D4 (22-dihydroergocalciferol) is a distinct form found in certain fungi. Unlike D3 from animal sources or human skin and D2 from yeast and fungi, D4 originates from 22,23-dihydroergosterol.

The Fungal Factories of Vitamin D4

Mushrooms are the primary source of naturally occurring vitamin D4, especially those exposed to ultraviolet (UV) radiation. UV exposure converts ergosterol in mushrooms to vitamin D2 and 22,23-dihydroergosterol to vitamin D4. Both wild and commercially UV-treated mushrooms contain D4. This includes:

Wild Mushrooms: Species like morels.
UV-Treated Commercial Mushrooms: Varieties such as maitake and portabella intentionally exposed to UV light.
Other Fungi: Yeast and other fungal organisms can also contain the precursor to vitamin D4.

The Human Impact: What We Know (And Don't Know)

The role of vitamin D2 and D3 in human health is well-documented, but the significance of vitamin D4 is much less clear. It's not a common component of diets or supplements.

Limited Biological Activity: Early studies suggested lower activity of D4 compared to D3 in animal models. The conversion of D4 into its active hormonal form and its activity in humans are not as researched as for D2 and D3.

Uptake and Metabolism: Research indicates D4 can be absorbed by cells, but its long-term impact on human vitamin D levels is unclear. Animal studies suggest D4 metabolites have a shorter half-life than D3. More research is needed on D4's biological role in humans.

Comparison of Vitamin D Forms (D2, D3, D4)


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)	Vitamin D4 (22-Dihydroergocalciferol)
Primary Source	Yeast, fungi, UV-treated mushrooms	Animal products, human skin via UV light	Fungi (UV-treated mushrooms)
Precursor Molecule	Ergosterol	7-Dehydrocholesterol	22,23-Dihydroergosterol
Commonality	Common in supplements, fortified foods, and vegetarian sources	Most common form in supplements and naturally occurring	Rare in standard diets; found primarily in UV-exposed fungi
Bioavailability in Humans	Readily absorbed, but often considered slightly less effective at raising serum levels than D3	Highly bioavailable and very effective at raising serum levels	Limited data available; animal studies show lower potency
Dietary Supplement	Widely available	Widely available	Not widely available
Research Status	Well-researched, common in clinical studies	Extensively researched, the benchmark for vitamin D	Scarcely researched in humans

Natural Sources of Vitamin D (General Context)

Focusing on established sources is key for adequate vitamin D intake. These primarily include D2 or D3:

Fatty Fish: Salmon, trout, mackerel, and tuna are excellent sources of D3.
Fish Liver Oils: Cod liver oil provides D3.
Animal Products: Beef liver, egg yolks, and cheese offer smaller amounts of D3.
Fortified Foods: Many foods like milk, plant-based milk, juice, and cereals are fortified with D2 or D3.

Conclusion

Vitamin D4, or 22-dihydroergocalciferol, is a form of vitamin D primarily found in UV-exposed mushrooms and other fungi. It differs from the more common and well-researched vitamins D2 and D3. While D4 can be absorbed, its biological activity and health benefits in humans are not clearly understood due to limited research. For reliable vitamin D intake, focus on sun exposure, fortified foods, or supplements containing D2 or D3. Further study is needed to determine the role of D4 in human nutrition. The NIH Office of Dietary Supplements provides authoritative information on vitamin D.

Frequently Asked Questions

No, they are distinct forms of vitamin D with different chemical structures and origins. D3 is primarily from animals and human skin, D2 from fungi and yeast, and D4 from UV-treated fungi.

You should only rely on mushrooms for vitamin D if they are specifically labeled as UV-treated or vitamin D-enhanced. Most commercially grown mushrooms are cultivated in the dark and contain negligible amounts of vitamin D.

Vitamin D4 is not included in most supplements because D2 and D3 are much better studied and proven to be effective for human health. D4's potency and human health benefits are not yet well understood.

While general vitamin D is critical for bone health, the specific effects of vitamin D4 are not well-researched in humans. More studies are needed to determine its effectiveness.

Yes, vitamin D4 is naturally produced in some fungi, particularly mushrooms, when they are exposed to UV light.

Animal studies have suggested that vitamin D4 has lower biological activity than vitamin D3. Its effectiveness in humans is still unknown.

The best way to get enough vitamin D is through moderate sun exposure, consuming fortified foods (like milk and cereal), eating fatty fish, and taking D2 or D3 supplements if recommended by a healthcare provider.