Vitamin D is a general term for a group of related compounds, while vitamin D3 is one specific form within that group. When you see “vitamin D” on a nutrition label or in health advice, it’s referring to the whole category. When you see “vitamin D3,” it’s pointing to cholecalciferol, the particular form your body makes from sunlight and the form found in most animal-based foods. The other main form is vitamin D2 (ergocalciferol), which comes from plants and fungi. Both work in your body, but they aren’t identical in how well they perform.
Two Forms: D3 and D2
Vitamin D3 and vitamin D2 are the two forms that matter for human health. Your body produces D3 naturally when UVB rays from sunlight hit your skin. The UV energy transforms a cholesterol compound in your skin cells into a precursor molecule, which then converts into vitamin D3 and gets picked up by proteins in your bloodstream. This is the same form found in fatty fish like salmon, trout, and mackerel, as well as in egg yolks and beef liver.
Vitamin D2 comes from a different source entirely. Plants, fungi, and yeast produce it when exposed to UV light. Mushrooms are the most common dietary source, especially varieties that have been treated with UV light to boost their content. Many older prescription vitamin D supplements use D2, and some fortified foods contain it as well.
Both forms increase vitamin D levels in your blood, but D3 tends to raise levels higher and maintain them longer than D2. The NIH notes this directly: “D3 might raise it higher and for longer than D2.” This is why most over-the-counter supplements now use D3, and why many doctors prefer it for correcting a deficiency.
How Your Body Uses Both Forms
Neither D3 nor D2 does anything useful in its raw form. Both are biologically inert when you first absorb them. Your liver converts whichever form you take into a compound called 25-hydroxyvitamin D, which is the form measured in blood tests. Then your kidneys perform a second conversion, turning it into the active hormone your cells actually use. This active form regulates calcium absorption, supports bone strength, and plays roles in immune function.
The two-step activation process is the same for both D2 and D3. The difference lies in how efficiently your body handles them upstream. D3 binds more readily to the transport proteins in your blood, which is likely why it produces a stronger, more sustained rise in blood levels compared to D2 at the same dose.
Where Each Form Shows Up in Food and Supplements
Almost all natural animal-based sources of vitamin D provide the D3 form. Fatty fish and fish liver oils are the richest sources. Egg yolks and cheese contain smaller amounts. Fortified milk in the U.S. typically provides about 120 IU per cup, and most brands use D3, though some fortified plant milks (soy, almond, oat) may use either form.
D2 is the form you’ll find in UV-treated mushrooms and in some fortified foods and prescription supplements. If a label just says “vitamin D” without specifying D2 or D3, check the ingredient list for “cholecalciferol” (that’s D3) or “ergocalciferol” (that’s D2).
Most supplement manufacturers now default to D3. The standard source is lanolin, a waxy substance extracted from sheep’s wool. For vegans and vegetarians, lichen-derived D3 is widely available. Lichen produces its own vitamin D3 as a defense against UV radiation, and the extracted form is chemically identical to lanolin-derived D3. Your body uses it exactly the same way, with no difference in effectiveness.
Which One Should You Take?
If you’re choosing a supplement, D3 is the better option for most people. It raises blood levels more effectively, it’s the form your body naturally produces, and it’s what the majority of clinical research has used. D2 still works, and if it’s what your doctor has prescribed or it’s the only vegan option available to you, it will raise your levels. You may just need a slightly higher or more frequent dose to achieve the same result.
The blood level you’re aiming for is the same regardless of which form you take. The National Academies consider a serum level of 20 ng/mL (50 nmol/L) or higher adequate for bone and overall health. Below 12 ng/mL (30 nmol/L), the risk of true deficiency increases, which can lead to weakened bones in adults and rickets in children. On the other end, levels above 50 ng/mL (125 nmol/L) are linked to potential harm, particularly above 60 ng/mL (150 nmol/L).
The Bottom Line on Labels
“Vitamin D” is the umbrella term. “Vitamin D3” is the specific, more potent form your skin makes and that comes from animal sources. “Vitamin D2” is the plant-derived alternative. When a supplement or food label says “vitamin D” without further detail, it could be either form. If the distinction matters to you, whether for effectiveness or dietary reasons, flip to the ingredients list. For most people buying a supplement off the shelf, D3 (cholecalciferol) is the straightforward choice.