Vitamin D is an umbrella term that covers two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The most important practical difference is that D3 raises your blood levels of vitamin D more effectively than D2, which is why most doctors recommend D3 for treating deficiency. But the two forms come from different sources, have slightly different molecular structures, and show up in different products on pharmacy shelves.
Where Each Form Comes From
Vitamin D2 is a plant and fungal product. It forms when a compound called ergosterol, found in fungi and some plants, gets exposed to ultraviolet light. Mushrooms are the standout natural food source, particularly shiitake, maitake, and oyster varieties. Some producers deliberately treat mushrooms like portobellos with UV light to boost their D2 content. You’ll also find D2 added to fortified foods like orange juice and cereals.
Vitamin D3 works differently. Your body produces it when UVB rays from sunlight hit your skin and convert a cholesterol-related compound (7-dehydrocholesterol) into D3 through a chain of chemical reactions. You also get D3 from animal foods: fatty fish, egg yolks, and cheese. Most over-the-counter D3 supplements are made from lanolin, an oil extracted from sheep’s wool that undergoes a multi-step chemical process to yield the final vitamin. For vegans, D3 supplements made from lichen (a composite organism of algae and fungi) offer a plant-based alternative.
How They Differ at the Molecular Level
Both D2 and D3 are classified as secosteroids, meaning they share a core ring structure that’s been “broken” open. The difference sits in their side chains. Vitamin D2 has an extra double bond between two carbon atoms and an additional methyl group that D3 lacks. This small structural tweak changes how each form behaves once it enters your body, particularly how tightly it binds to transport proteins in the blood and how efficiently your liver converts it into its next active form.
What Happens After You Take Them
Both D2 and D3 follow the same basic pathway. After absorption, they travel to the liver, where they’re converted into 25-hydroxyvitamin D, the form that doctors measure in a standard blood test. From there, the kidneys convert it into the fully active hormone your body uses for calcium absorption, bone maintenance, and immune function.
The catch is that D2 doesn’t perform as well at each step. It binds less efficiently to the proteins that carry vitamin D through your bloodstream, and it’s cleared from the body faster. The net result: taking the same dose of D2 produces a smaller, shorter-lived rise in blood levels compared to D3. This is why studies consistently find D3 more effective at raising and sustaining your vitamin D status over time.
Why D2 Still Exists as a Supplement
Given that D3 is more potent, you might wonder why D2 supplements are still on the market. A few reasons keep D2 relevant:
- Cost. D2 supplements are often cheaper to produce and buy.
- Dietary restrictions. Because D2 comes from plants and fungi rather than animals, it’s inherently vegan-friendly. While lichen-derived D3 also works for vegans, D2 remains the more widely available plant-based option.
- Prescription availability. High-dose vitamin D prescriptions have historically used D2, though this is shifting as D3 becomes more commonly prescribed.
Stability During Cooking
If you’re getting vitamin D from food, you might worry about losing it during cooking. Research published in Food Chemistry tested both forms in oil, fish, and mushrooms under various cooking conditions and found no meaningful difference in stability between D2 and D3. Both held up well at room temperature (96 to 99% retained) and lost more at higher heat: pan-frying at high temperatures preserved about 70 to 72%, while oven baking at moderate temperatures kept 85 to 89%. Adding an acidic ingredient like lemon juice actually helped preserve both forms, with retention hitting 97 to 99%. The bottom line: cooking method matters more than which form of vitamin D your food contains.
How Much You Need
The recommended daily amount doesn’t distinguish between D2 and D3. For most adults aged 19 to 70, the target is 15 mcg (600 IU) per day. Adults over 70 need slightly more at 20 mcg (800 IU). Infants up to 12 months have an adequate intake set at 10 mcg (400 IU), and children aged 1 through 18 should aim for 15 mcg (600 IU). The same recommendations apply during pregnancy and lactation: 15 mcg (600 IU).
Keep in mind that if you’re using D2 to meet these targets, you may need to take it more frequently or at a somewhat higher dose to achieve the same blood levels you’d get from D3. Your doctor can check your 25-hydroxyvitamin D level with a simple blood test and adjust your supplement accordingly.
Which One Should You Choose
For most people, D3 is the better pick. It’s more effective at raising blood levels, widely available over the counter, and comes in both animal-derived (lanolin) and vegan (lichen) forms. D2 is a reasonable choice if cost is a concern or if it’s the form included in a fortified food you already eat regularly. Either form counts toward your daily intake, and both end up as the same active hormone in your body. The difference is simply how efficiently they get there.