Vitamin D and vitamin D3 are not exactly the same thing. “Vitamin D” is an umbrella term covering two forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). When a supplement label simply says “vitamin D” without specifying, it could be either form. In practice, though, most people use “vitamin D” and “vitamin D3” interchangeably because D3 is the form your body makes naturally and the one found in most supplements today.
Two Forms of Vitamin D
Vitamin D2 comes from plants and fungi. It’s derived from ergosterol, a compound produced by mushrooms and yeast, and it was the original form used in supplements and fortified foods. Vitamin D3, on the other hand, is the form your skin produces when exposed to sunlight. It’s synthesized from a cholesterol compound called 7-dehydrocholesterol, which converts to D3 under UV radiation.
The two forms are structurally similar but differ in their side chains. D2 has an extra methyl group and a double bond that D3 lacks. This small chemical difference affects how your body processes each one, which is why the distinction matters.
Both Follow the Same Activation Path
Whether you take D2 or D3, your body runs it through the same two-step activation process. First, the liver converts it into a circulating form called 25-hydroxyvitamin D, which is what blood tests measure. Then the kidneys convert that into the active hormone your cells actually use. This active form regulates calcium absorption, supports bone health, and plays roles in immune function.
So both D2 and D3 “work” in the sense that your body can use either one. The question is how well.
D3 Raises Blood Levels More Effectively
A meta-analysis of randomized controlled trials published in The American Journal of Clinical Nutrition found that D3 supplementation raised blood levels of 25-hydroxyvitamin D significantly more than D2. This difference was especially pronounced with larger, less frequent doses (weekly or monthly). When people took daily doses, the gap between D2 and D3 narrowed considerably.
This means if your doctor prescribes a high-dose weekly supplement, D3 is clearly the better choice. For a standard daily supplement, both forms can maintain adequate levels, though D3 still has a slight edge overall. This is one reason D3 has become the default in most over-the-counter supplements.
Where Each Form Comes From
In food, D3 is found in animal sources. Fatty fish like salmon, trout, tuna, and mackerel are the richest natural sources. Beef liver, egg yolks, and cheese contain smaller amounts. Fortified milk (about 120 IU per cup) and fortified cereals also provide vitamin D, though labels don’t always specify which form.
D2 comes primarily from mushrooms, especially varieties exposed to UV light to boost their content. It’s also the form produced by yeast, which is why some fortified plant milks and orange juices use D2.
Very few foods naturally contain meaningful amounts of vitamin D in either form. Most people in the United States get the majority of their dietary vitamin D from fortified products.
Supplements: Lanolin, Lichen, and Fungi
Most D3 supplements are made from lanolin, a waxy substance extracted from sheep’s wool. After shearing, the wool is washed to collect lanolin, which is then processed and exposed to UV light to produce D3. This makes standard D3 supplements unsuitable for vegans.
A plant-based alternative exists: lichen, a small organism that’s part fungus and part algae. Lichen naturally produces D3 when exposed to sunlight, using the same UV-driven process that happens in human skin. The D3 extracted from lichen is chemically identical to lanolin-derived D3 with no difference in how your body absorbs or uses it. If you follow a vegan diet and want D3 specifically, lichen-sourced supplements are widely available.
D2 supplements are always plant-derived, typically from UV-exposed yeast or mushrooms. This made D2 the go-to vegan option before lichen-based D3 became common.
Your Body’s Own Production
Your skin makes D3, not D2. When UVB rays hit exposed skin, they trigger the conversion of 7-dehydrocholesterol into pre-vitamin D3, which then transforms into D3 through body heat. For people with lighter skin (type II), exposing the face, hands, and arms to midday sun for about 12 minutes at a UV index of 7, two to three times a week, produces sufficient vitamin D3. People with darker skin need longer exposure because melanin reduces UV penetration.
Latitude, season, cloud cover, sunscreen, and clothing all affect this process. During winter months at higher latitudes, UVB radiation is too weak to trigger meaningful D3 production, which is why supplementation becomes important.
How Much You Need
The NIH recommends 600 IU (15 mcg) daily for most people ages 1 through 70, rising to 800 IU (20 mcg) for adults over 71. Infants need 400 IU (10 mcg). These recommendations apply regardless of whether you’re getting D2 or D3.
A blood level of 20 ng/mL or higher is generally considered sufficient for bone and overall health. Below 12 ng/mL qualifies as deficiency, which can lead to weakened bones. Levels above 50 ng/mL are linked to potential harm, particularly above 60 ng/mL. Vitamin D is fat-soluble, meaning excess amounts are stored in body tissue rather than flushed out, so more is not always better.
Which One Should You Choose?
For most people, D3 is the better supplement choice. It’s more effective at raising and maintaining blood levels, it’s the form your body produces naturally, and it’s what you’ll find in the majority of supplements on store shelves. If a bottle just says “vitamin D” on the front, check the ingredients or supplement facts panel for “cholecalciferol” (D3) or “ergocalciferol” (D2).
D2 still works, and if it’s what your doctor has prescribed or what’s available to you, it will raise your vitamin D levels. The practical difference between the two forms is modest with daily dosing. But given the choice, D3 is the more efficient option across the board.