Vitamin D2 and D3 are two forms of the same vitamin that differ in where they come from, how well your body uses them, and how long they last in your bloodstream. Both can raise your vitamin D levels, but D3 is generally more effective and is the form your body produces naturally from sunlight. Understanding the distinction matters when you’re choosing a supplement or trying to get more vitamin D from food.
Where Each Form Comes From
Vitamin D3, also called cholecalciferol, is the form your skin makes when it’s exposed to sunlight. UVB rays in the 290 to 315 nanometer range hit a cholesterol-related compound in your skin cells and convert it into D3, which then moves into your bloodstream. This is the same form found in animal foods like fatty fish, egg yolks, and beef liver.
Vitamin D2, called ergocalciferol, comes from plants and fungi. Mushrooms are the primary food source, and some commercial mushrooms are treated with UV light to boost their D2 content significantly. Half a cup of UV-exposed white mushrooms contains about 366 IU, while untreated portabella mushrooms provide just 4 IU per serving. D2 supplements are made by exposing yeast to UV radiation, which converts a compound called ergosterol into vitamin D2.
The two molecules are structurally similar but not identical. They differ in the shape of their side chains, and that small structural difference affects how your body processes them.
How Your Body Processes Them Differently
Both D2 and D3 go through the same basic activation pathway. Your liver converts either form into a circulating compound (called 25-hydroxyvitamin D), which is what blood tests measure. Your kidneys then convert that into the active hormone your body actually uses.
The key difference is efficiency. D3 produces a more sustained rise in blood levels of 25-hydroxyvitamin D. One reason: D3 stays in your system longer. The circulating half-life of D3 is about 15.1 days, compared to 13.9 days for D2. That roughly one-day difference may sound small, but it compounds over time, especially with daily supplementation. Your body clears D2 faster, so it builds up less effectively in your blood.
D3 also binds more effectively to the proteins that carry vitamin D through your bloodstream. This means more of it reaches the tissues that need it rather than being broken down and excreted.
Food Sources at a Glance
Most vitamin D in the food supply is D3. Fortified milk, the single largest dietary source for most Americans, uses D3 at about 120 IU per cup. The richest natural sources are fatty fish: a 3-ounce serving of cooked sockeye salmon delivers 570 IU, and rainbow trout provides 645 IU. A tablespoon of cod liver oil tops the list at 1,360 IU.
On the lower end, a scrambled egg provides about 44 IU (all in the yolk), canned tuna offers 40 IU per 3-ounce serving, and cheddar cheese has just 17 IU per 1.5-ounce portion.
D2 sources are limited mostly to mushrooms and some fortified plant milks. Fortified soy, almond, and oat milks typically contain 100 to 144 IU per cup, and these may use either D2 or D3 depending on the brand. Fortified cereals provide around 80 IU per serving.
Supplements: Which Form Is Better?
D3 is the more effective supplement for raising and maintaining your blood levels of vitamin D. At equivalent doses, D3 consistently outperforms D2 in clinical comparisons. If your goal is to correct a deficiency or keep your levels steady, D3 is the stronger choice.
D2 supplements do still work. They were the standard prescription form for decades, and they will raise your levels. They’re just less efficient at doing so, particularly for long-term maintenance. D2 is also more sensitive to humidity and temperature fluctuations, which means it may degrade faster on the shelf than D3.
For people following a vegan diet, D2 was historically the only plant-based option. That’s changed. Vegan D3 supplements are now made from lichen, a symbiotic organism that produces cholecalciferol the same way animal skin does. Lichen-derived D3 is typically extracted using food-grade solvents like olive oil, which differs from conventional D3 supplements made from lanolin (sheep wool grease) that require industrial chemical processing. The end product is the same molecule, just sourced differently.
Which One Should You Choose?
For most people, D3 is the better option. It raises blood levels more effectively, stays active in your body longer, and is widely available in both animal-derived and vegan forms. If you’re already taking D2 and your blood levels look good, there’s no urgent reason to switch. But if you’re starting fresh or your levels are low, D3 gives you more reliable results per dose.
The form matters less than consistency. Vitamin D is fat-soluble, so taking it with a meal that contains some fat improves absorption regardless of which type you choose. And because fortified foods provide most of the vitamin D in American diets, checking whether your milk, cereal, or plant milk uses D2 or D3 can help you understand what you’re actually getting each day.