Where is 7-Dehydrocholesterol Found?

December 21, 2025 •

3 min read

An estimated 40% of the worldwide population is vitamin D deficient, which brings attention to its precursor, 7-dehydrocholesterol (7-DHC). 7-dehydrocholesterol, also known as provitamin D3, is primarily found in the deeper layers of mammalian skin, where it is converted into vitamin D3 through exposure to ultraviolet B (UVB) radiation from sunlight. It is a critical component of the cholesterol synthesis pathway and is also present in certain animal products and industrial sources.

Quick Summary

This article explores the biological and external sources of 7-dehydrocholesterol (7-DHC). It examines its location within human and animal bodies, such as the skin and milk, its role as a provitamin D3, and its industrial extraction. Information about its function as a cholesterol precursor and the implications of its accumulation in certain genetic disorders is also discussed.

Key Points

Skin's Vitamin D Factory: The highest concentrations of 7-dehydrocholesterol (7-DHC) are found in the stratum basale and stratum spinosum layers of mammalian skin, where it acts as provitamin D3.
Sunlight's Catalyst: UVB radiation from sunlight triggers the photochemical conversion of 7-DHC in the skin into vitamin D3.
Cholesterol Precursor: 7-DHC is a vital intermediate in the cholesterol biosynthesis pathway in mammals, preceding the final step of conversion to cholesterol.
Animal-Derived Sources: Besides skin, 7-DHC can be found in the milk of various mammals, the lanolin of wool-bearing animals, and the fatty tissues of fish.
Diagnostic Implications: Elevated levels of 7-DHC in tissues and fluids are a key biomarker for genetic disorders like Smith-Lemli-Opitz syndrome.
Industrial Production: 7-DHC extracted from lanolin is a major source for the commercial manufacturing of vitamin D3 supplements.

7-Dehydrocholesterol in Mammals: The Body's Internal Source

In mammals, including humans, 7-dehydrocholesterol (7-DHC) is a naturally occurring sterol crucial for cholesterol biosynthesis. It is the final precursor before cholesterol in this metabolic pathway and serves as provitamin D3. Human skin, particularly the stratum basale and stratum spinosum layers, contains the highest concentrations of 7-DHC.

Exposure to UVB radiation converts 7-DHC in the skin into previtamin D3, which then changes to vitamin D3 (cholecalciferol). This process is a primary way humans produce vitamin D, with sufficient 7-DHC in the skin for typical needs. 7-DHC is also found in the milk of mammals like cows, offering a dietary source that can be converted to vitamin D3 internally or via UV exposure. Genetic conditions such as Smith-Lemli-Opitz syndrome (SLOS) involve a deficiency in the enzyme that converts 7-DHC to cholesterol, leading to a buildup of 7-DHC.

Animal and Plant Sources of 7-Dehydrocholesterol

Besides endogenous production in mammals, 7-DHC exists in other biological sources, both animal and, to a lesser extent, plant-based.

Animal-Derived Sources

Fatty Fish and Fish Waste: Fatty fish are rich in 7-DHC, which is converted to vitamin D3. Fish waste is also explored for its 7-DHC content for vitamin D3 extracts.
Wool (Lanolin): Lanolin from sheep is a significant industrial source of 7-DHC. This is processed and irradiated to create vitamin D3 for supplements.
Insects: 7-dehydrocholesterol is a precursor for the hormone ecdysone, essential for molting in some insects.

Plant-Based Sources

While not abundant in fungi, some algae produce 7-DHC. Ergosterol, a different provitamin found in many plants and fungi, converts to vitamin D2 upon UV exposure and is used in vegan supplements. Lichen (Cladonia rangiferina) is also used for vegan vitamin D3, likely due to its 7-DHC content.

Comparison of Key 7-DHC Sources


Feature	Human Skin	Lanolin (Wool)	Fatty Fish/Waste	Algae/Lichen	Genetic Disorders (SLOS)
Source Type	Endogenous (Mammal)	Industrial/External	External/Food	External/Food	Endogenous (Mammal)
Primary Function	Provitamin D3 for synthesis	Industrial source for D3	Food source of D3 precursor	Vegan D3 source	Diagnostic biomarker
Mechanism	UVB radiation conversion	UV irradiation during processing	Natural synthesis	UV irradiation conversion	Defective enzyme causes buildup
Conversion Product	Vitamin D3 (Cholecalciferol)	Commercial Vitamin D3	Commercial Vitamin D3	Vitamin D3 (Lichen)	Accumulates unconverted 7-DHC
Level of 7-DHC	Sufficient for most needs	High in raw material	High concentration in certain species	Trace amounts, variable	Pathologically elevated

Conclusion

7-dehydrocholesterol is a vital biological compound, primarily known as the precursor for vitamin D3 production in mammalian skin with sun exposure. It is also found in various animal and industrial sources. Understanding its distribution helps in comprehending natural physiological processes and industrial uses, from vitamin D supplements to disease diagnosis. Ongoing research continues to reveal new aspects of this molecule's role in biology and health.

References

Huang, J., Guo, J., & Chen, J. (2015). 7-Dehydrocholesterol (7-DHC), But Not Cholesterol, Causes Aberrant Transforming Growth Factor-β Signaling in Target Cells. American Journal of Physiology, 308(12), H1414–H1423. DOI: 10.1152/ajpcell.00287.2014
Martelli, A., D’Avino, F., Zampolli, F., ... & Zampolli, A. (2021). From 7-dehydrocholesterol to vitamin D3: Optimization of UV conversion from fish waste. Journal of Cleaner Production, 290, 125191. DOI: 10.1016/j.jclepro.2020.125191
Wacker, M., & Holick, M. F. (2013). 7-Dehydrocholesterol - Wikipedia. Retrieved October 12, 2025, from https://en.wikipedia.org/wiki/7-Dehydrocholesterol
Bikle, D. D. (2013). Vitamin D: Production, Metabolism, and Mechanism of Action. Endotext. Retrieved October 12, 2025, from https://www.ncbi.nlm.nih.gov/books/NBK278935/
Nagayoshi, Y., Ito, T., Sato, S., ... & Tomita, F. (2016). Process for producing 7-dehydrocholesterol and vitamin d3. US Patent Application Publication US 2016/0332964 A1. Retrieved October 12, 2025, from https://patents.google.com/patent/US20160332964A1/en

Frequently Asked Questions

7-dehydrocholesterol is important because it is the natural precursor, or provitamin D3, that our bodies use to produce vitamin D3 in the skin upon exposure to sunlight. It is also a critical component in the body's cholesterol synthesis pathway.

While 7-dehydrocholesterol is not typically a significant part of the human diet, it is present in small amounts in certain animal products, such as the milk of some mammals, and is found in higher concentrations in fatty fish and their waste.

UVB radiation from sunlight provides the energy needed to open a specific chemical ring structure in the 7-dehydrocholesterol molecule, converting it into an intermediate form called previtamin D3. This previtamin then undergoes a temperature-dependent rearrangement to become vitamin D3.

Some algae can produce 7-dehydrocholesterol, but most plants produce a different provitamin, ergosterol, which is converted into vitamin D2 upon UV irradiation. Lichen is also known to produce vegan vitamin D3 from 7-DHC.

High levels of 7-dehydrocholesterol can indicate a problem with the body's cholesterol synthesis process. It is a diagnostic marker for Smith-Lemli-Opitz syndrome (SLOS), a genetic disorder where the enzyme that converts 7-DHC to cholesterol is deficient.

Industrially, 7-dehydrocholesterol is often extracted from lanolin, a wax from sheep's wool. The extracted 7-DHC is then irradiated with UVB light to produce vitamin D3, which is used in dietary supplements.

7-dehydrocholesterol is classified as a zoosterol because it is a sterol produced by animals (zoo-), in contrast to phytosterols, which are produced by plants.