The Name of the Vitamin D: Understanding its Different Forms

January 7, 2026 •

3 min read

Did you know that vitamin D is not a single nutrient but a collection of fat-soluble compounds called calciferols? For those asking, 'What is the name of the vitamin D?' the answer is more complex than you might expect, as it refers to two primary forms found in foods and supplements, as well as the active hormonal form your body creates.

Quick Summary

The term 'vitamin D' refers to several forms, primarily ergocalciferol (D2) from plants and cholecalciferol (D3) from animals. These are converted by the body into the active hormone calcitriol, which helps regulate calcium and phosphorus for bone and immune health.

Key Points

Name Clarification: 'Vitamin D' is a general term for a group of compounds called calciferols, not a single substance.
Forms of Vitamin D: The two most common forms are D2 (ergocalciferol), from plants, and D3 (cholecalciferol), produced in animal skin upon sun exposure.
The Active Hormone: Both D2 and D3 are converted in the liver and kidneys into the active hormone, calcitriol, which is essential for biological function.
Key Function: Vitamin D's primary role is to regulate calcium and phosphorus absorption, which is vital for maintaining strong, healthy bones and teeth.
Deficiency Consequences: Insufficient vitamin D can lead to bone disorders like rickets in children and osteomalacia in adults, characterized by softened bones and increased fracture risk.
Sunlight and Diet: While sun exposure is a major source, many people must rely on dietary sources, fortified foods, and supplements to meet their needs, especially during winter months.

The Core Names: Calciferol and its Forms

While the term 'vitamin D' is used universally, it is technically a class of compounds known as calciferols. Within this class, two forms are most important for human health: vitamin D2 and vitamin D3. The specific source of the vitamin determines which name is used, and it is crucial for understanding how the body utilizes this vital nutrient.

Vitamin D2: Ergocalciferol

One of the main forms of vitamin D is ergocalciferol, commonly known as vitamin D2. It is derived from plants and fungi when exposed to ultraviolet (UV) light and is often used to fortify foods or in vegan supplements.

Vitamin D3: Cholecalciferol

The other major form is cholecalciferol, or vitamin D3. It is synthesized in the skin from sun exposure (UVB radiation) and found in animal-based foods like fatty fish and egg yolks. D3 is generally considered more effective at raising and maintaining blood levels.

How Your Body Processes Vitamin D

Vitamin D is inactive until converted by the body. The liver first converts D2 or D3 into calcifediol (25-hydroxyvitamin D), which indicates vitamin D status in blood tests. The kidneys then convert calcifediol into the active hormone, calcitriol (1,25-dihydroxyvitamin D), which regulates calcium levels.

Sources of the Sunshine Vitamin

Vitamin D can be obtained from:

Sunlight Exposure: UVB rays trigger D3 synthesis in skin, affected by latitude, season, time, and skin tone.
Food Sources: Naturally in fatty fish, egg yolks, cheese, and beef liver, plus fortified products like milk and cereals.
Dietary Supplements: D2 or D3 supplements are common, especially for those with limited sun exposure or dietary intake.

Key Functions of Vitamin D in the Body

Vitamin D is crucial for several bodily functions.

Promoting Calcium Absorption

It significantly enhances calcium absorption from the intestines. Insufficient vitamin D hinders calcium absorption, potentially leading to the body drawing calcium from bones.

Supporting Bone Health

Along with calcium and phosphate, vitamin D is vital for strong bones and teeth. Deficiency can cause rickets (soft, weak bones and deformities) in children and osteomalacia (soft bones, pain, increased fracture risk) in adults.

A Role in Immune Function

Vitamin D receptors in immune cells suggest it modulates immune responses and may help reduce inflammation and fight infections.

Vitamin D2 vs. Vitamin D3: A Comparison


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)
Source	Plants, fungi, UV-irradiated yeast.	Animal foods, lichen, sun exposure.
Potency	Less potent at raising serum levels.	More effective at increasing and sustaining levels.
Absorption	Well absorbed.	Well absorbed, especially with fat.
Shelf Life	Shorter and less stable.	More stable, longer shelf life.
Vegan Status	Always vegan.	Traditionally animal-derived; vegan options from lichen exist.

Recognizing a Vitamin D Deficiency

Symptoms can be subtle, including fatigue, bone pain, muscle weakness, frequent illness, and potential mood changes.

Who is at risk?

Risk factors include older age (reduced skin synthesis), being a breastfed infant (low levels in breast milk), having dark skin (melanin blocks UV), limited sun exposure, and malabsorption conditions.

Conclusion: The Importance of a Multi-faceted Nutrient

'Vitamin D' refers to calciferols, specifically D2 and D3, converted to the active hormone calcitriol. Calcitriol is essential for calcium regulation, bone health, and immune function. Sources include sun exposure, diet (fatty fish, fortified foods), and supplements. Maintaining adequate levels is vital for health and preventing bone disorders, and consultation with a healthcare provider is recommended.

For more detailed, scientific information on vitamin D, refer to the National Institutes of Health (NIH) Office of Dietary Supplements fact sheets, which are regularly updated with the latest research on its health effects and recommended intake. NIH Office of Dietary Supplements, Vitamin D Fact Sheet

Frequently Asked Questions

The scientific name for the group of compounds is calciferol. The two most relevant forms for humans are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).

The two main types are vitamin D2 (ergocalciferol), which comes from plants and fungi, and vitamin D3 (cholecalciferol), which is produced in animal skin and also available from certain animal products.

Evidence suggests that vitamin D3 is more effective at raising and sustaining blood vitamin D levels over a longer period compared to vitamin D2. However, both forms are effective at preventing or curing vitamin D deficiency.

Your body can get vitamin D from three primary sources: sunlight exposure on your skin, dietary intake from fatty fish and fortified foods, and dietary supplements.

After intake, vitamin D is converted in the liver and kidneys into its active hormonal form, called calcitriol (1,25-dihydroxyvitamin D).

A deficiency can lead to bone pain, muscle weakness, fatigue, and an increased risk of bone disorders like rickets in children and osteomalacia in adults.

Yes, excessive intake of vitamin D, typically from high-dose supplements, can cause toxicity, which may result in high calcium levels in the blood, nausea, vomiting, and confusion. Toxicity from sun exposure is not possible because the body self-regulates production.

Yes, vitamin D deficiency is common worldwide. Populations at higher risk include older adults, breastfed infants, people with darker skin, and individuals with limited sun exposure.