Vitamin D2 vs D3

Vitamin D comes in two main forms, D2 and D3, which are often discussed as if they were one substance. They differ in where they come from and in some details of how the body handles them, yet both feed into the same vitamin D pathway. This page compares them for general understanding.

What vitamin D2 is

Vitamin D2, also called ergocalciferol, comes largely from plant and fungal sources. Certain fungi and yeasts produce it, especially when exposed to ultraviolet light, and it is the form found in some fortified foods and dietary products. Like all forms of vitamin D, D2 is not fully active as it stands; the body must process it through the liver and kidneys before it becomes the active hormone form that acts on tissues. D2 has historically been a common form used in supplementation and food fortification.

What vitamin D3 is

Vitamin D3, also called cholecalciferol, is the form that the skin makes when exposed to sunlight, and it is also found in some animal-source foods. Because the body produces D3 naturally in response to ultraviolet light, it is sometimes described as the form the human body is most accustomed to making for itself. Like D2, D3 must be processed by the liver and kidneys to become the active hormone. D3 is widely used in supplements and fortification as well.

How they relate

Both D2 and D3 are members of the vitamin D family and converge on the same biological pathway. After entering the body, each is converted in the liver to a storage form and then, in the kidneys, to the active hormone that regulates calcium and supports bone health, among other roles. Blood tests for vitamin D status generally aim to capture the overall pool, which can include both forms. So while D2 and D3 start from different sources, they are processed by the same machinery and ultimately serve the same downstream functions.

How they compare side by side

The points below summarise commonly discussed differences. They describe general distinctions, not rules, and the entries here are illustrative; ongoing research continues to refine how the two forms compare.

For background on related hormones and vitamins, see the hormones index; for how blood samples are collected, see the blood tests overview. Related conditions appear in the conditions index, treatment context lives in the treatments index, and you can browse more side-by-side explanations in the comparisons index.

When each matters

The distinction matters most when reading product labels or discussing vitamin D status, because the label tells you which form is involved and where it came from. For people following plant-based diets, the plant- and fungus-derived nature of D2 can be relevant, while D3's link to sunlight and animal sources is a different consideration. Whether the two forms are equivalent in raising and maintaining vitamin D status is an area where research continues, so general statements should be read cautiously. For a related theme of comparing how the body processes related molecules, see insulin vs glucagon.

Common points of confusion

A common point of confusion is treating "vitamin D" as a single substance when it actually refers to a family that includes both D2 and D3. Another is assuming the two forms are completely interchangeable; they share the same downstream pathway but differ in source and in some details of how the body handles them, and comparisons remain an active research topic. A third is overlooking that neither form is active as taken in — both must be processed by the liver and kidneys first. Keeping these points in mind helps when reading labels or test results, and a clinician can explain what a given vitamin D measurement means in context.