What are the variants of vitamin D?

November 20, 2025 •

3 min read

The majority of people receive some vitamin D from sunlight exposure, but there are multiple forms of this vital nutrient. Exploring the specific variants of vitamin D helps clarify their origins, physiological roles, and how they contribute to overall health and well-being.

Quick Summary

The vitamin D family includes primary variants D2 (ergocalciferol) and D3 (cholecalciferol), which differ in their sources and potency. D2 is derived from plants and fungi, while D3 is produced in the skin from sun exposure and found in animal-based foods. Both forms are converted into active metabolites by the body, but studies show D3 is more effective at raising blood levels for longer periods.

Key Points

Two Primary Forms: The main variants are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), which differ in their origin and potency.
Source Differences: D2 is derived from plant sources like fungi and fortified foods, while D3 is synthesized in the skin from sunlight exposure and found in animal products.
Conversion to Active Form: Both D2 and D3 are inactive until metabolized by the liver and kidneys into calcitriol, the active hormonal form that regulates calcium.
D3 Is More Potent: Research indicates that vitamin D3 is more effective than D2 at increasing and sustaining overall vitamin D blood levels, making it the preferred choice for supplementation.
Sunlight is a Double-Edged Sword: Sun exposure is the most efficient natural source of D3, but health experts recommend balancing exposure with sun protection due to the risk of skin cancer.
Status is Measured by Metabolites: Vitamin D status is typically measured by testing for 25-hydroxyvitamin D (calcifediol) in the blood, which is the main circulating metabolite of both D2 and D3.
Supplements Vary: Supplements can contain either D2 or D3, and vegan options for D3 derived from lichen are also available for those who avoid animal products.

The variants of vitamin D are a group of fat-soluble compounds crucial for various bodily functions, particularly regulating calcium and phosphate absorption for bone health. The two most significant variants are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both are inactive until converted into their active hormonal form, calcitriol, through a two-step process in the liver and kidneys. Understanding their differences in origins, metabolism, and potency is key to optimizing vitamin D status.

Vitamin D2 (Ergocalciferol): The Plant-Based Variant

Ergocalciferol, or vitamin D2, is primarily sourced from plants and fungi. It is produced when ergosterol is exposed to ultraviolet B (UVB) radiation. UV-exposed mushrooms are a notable natural food source. Many fortified foods, especially vegan options, use vitamin D2.

Source: Plant-based foods like UV-treated mushrooms and fortified vegan products.
Production: Formed from the irradiation of ergosterol.
Uses: Common in supplements, particularly for vegans.

Vitamin D3 (Cholecalciferol): The Animal-Based & Sun-Induced Variant

Vitamin D3, or cholecalciferol, is produced naturally in human skin upon exposure to UVB sunlight. UVB rays convert 7-dehydrocholesterol into previtamin D3, which then becomes vitamin D3. This is the most efficient natural source. D3 is also found in animal products like fatty fish and egg yolks and is a common supplement choice derived from sources like lanolin or lichen.

Source: Sunlight exposure and animal-based foods, plus fortified dairy.
Production: Synthesized in the skin from 7-dehydrocholesterol following UVB exposure.
Uses: Preferred supplement form due to higher efficacy.

The Metabolic Journey: From Inactive to Active

Both D2 and D3 are biologically inactive and require two hydroxylation steps to become the active hormone, calcitriol.

First Hydroxylation (Liver): The liver converts D2 and D3 into their 25-hydroxyvitamin D forms (25(OH)D2 and 25(OH)D3). This circulating form, calcifediol, is used to assess vitamin D status.
Second Hydroxylation (Kidneys): The kidneys convert calcifediol into the active hormone, 1,25-dihydroxyvitamin D, or calcitriol. Calcitriol regulates calcium and phosphate levels.

Comparison: Vitamin D2 vs. Vitamin D3

Studies show vitamin D3 is more effective at increasing and maintaining blood levels of calcifediol than D2.


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Source	Plants, fungi, fortified foods	Sunlight, animal-based foods, fortified dairy
Origin	Formed from UV irradiation of ergosterol	Synthesized in skin via UV radiation of 7-dehydrocholesterol
Potency	Less effective in raising blood levels	More effective at increasing serum 25(OH)D levels
Form in Supplements	Used in many supplements	Preferred form in supplements
Vegan Friendly	Often used in vegan supplements	Vegan versions from lichen available
Chemical Stability	May be more sensitive	Generally considered more stable

Other Forms and Metabolites

Beyond D2 and D3, the vitamin D family includes metabolites.

Calcifediol (25-hydroxyvitamin D): The main circulating, inactive form measured in blood tests.
Calcitriol (1,25-dihydroxyvitamin D): The biologically active, hormonal form.
Vitamin D4 and D5: Lesser-known forms, not medically significant.

Conclusion

Vitamin D encompasses several variants with distinct origins and properties. D2 and D3 are primary variants, both vital for calcium regulation after conversion to calcitriol. Research consistently shows D3 is more potent and effective at raising vitamin D levels. For most, a combination of sunlight, fortified foods, and potentially D3 supplementation is effective. Understanding variant differences is key to choosing supplements, especially for vegans or those with absorption issues.

The Role of Sun Exposure in Creating Vitamin D3

Sunlight exposure for vitamin D comes with skin cancer risks. Health organizations recommend limiting sun exposure and using protection. For limited sun exposure, supplements are crucial.

Sources and references: ODS. (2025). Vitamin D - Health Professional Fact Sheet. National Institutes of Health. Wikipedia. (2025). Vitamin D. Wikimedia Foundation. InstaCare. (2024). Vitamin D2 vs. D3: What’s the Difference?. InstaCare Blog. NCBI. (2025). Overview of Vitamin D. Dietary Reference Intakes for... - NCBI. The Nutrition Source. (2025). Vitamin D. Harvard T.H. Chan School of Public Health. ScienceDirect. (2025). Vitamin D Metabolism - an overview. ScienceDirect Topics. MNT. (2025). Vitamin D2 vs. D3: Differences, benefits, sources. Medical News Today. Healthline. (2023). Vitamin D2 vs. D3: What's the Difference?. Healthline Nutrition. ODS. (2025). Vitamin D - Health Professional Fact Sheet. National Institutes of Health. NHS. (2025). Vitamin D. NHS website. Yale Medicine. (2018). Vitamin D Myths 'D'-bunked. Yale Medicine News.

Frequently Asked Questions

The main difference lies in their source and chemical structure. Vitamin D2 (ergocalciferol) is plant-based, found in mushrooms and fortified vegan foods. Vitamin D3 (cholecalciferol) is produced in the skin upon sun exposure and is also found in animal products. Studies suggest D3 is more potent in raising and maintaining blood vitamin D levels.

For most people, vitamin D3 is considered superior due to evidence suggesting it is more effective at raising and sustaining blood levels of vitamin D. However, both forms are effective at preventing deficiency, and some may choose D2 for dietary reasons, such as following a vegan lifestyle.

The body activates vitamin D through a two-step hydroxylation process. First, the liver converts D2 or D3 into 25-hydroxyvitamin D. Next, the kidneys convert this metabolite into the active hormonal form, calcitriol, which the body can use.

While sun exposure is an efficient way to produce vitamin D3, many factors, including latitude, season, skin tone, and sunscreen use, can limit production. Experts recommend a balanced approach that may include supplements to ensure adequate intake, especially during winter months or for those with limited sun exposure.

For many, especially those who live in northern latitudes, have limited sun exposure, or follow a restrictive diet, supplements are often necessary to maintain adequate levels of vitamin D. Few foods naturally contain significant amounts, making it difficult to get enough from diet alone.

Calcitriol is the biologically active hormonal form of vitamin D, produced primarily in the kidneys. It is responsible for regulating calcium and phosphate absorption from the gut and is crucial for bone health and other cellular functions.

Vitamin D status is most commonly measured by a blood test that checks the level of 25-hydroxyvitamin D (calcifediol), which is the major circulating form of the vitamin in the body and a good indicator of overall stores.