Vitamin D2 and D3 are both forms of vitamin D, but they come from different sources, behave differently in your body, and aren’t equally effective at raising your vitamin D levels. D3 (cholecalciferol) is the form your skin produces naturally from sunlight and the form found in animal-based foods. D2 (ergocalciferol) comes from fungi and is commonly used in fortified foods. For most people, D3 is the better choice for supplementation.
Where Each Form Comes From
Vitamin D2 is naturally found in mushrooms and yeast. When mushrooms are exposed to UV light, they convert a compound called ergosterol into D2, much like your skin produces D3 from sunlight. Most fortified foods, including cereals, orange juice, and plant-based milks, contain D2. It’s also the form most commonly found in high-dose prescription supplements.
Vitamin D3 is found in animal-based foods: fatty fish like salmon and trout, egg yolks, beef liver, sardines, and cheese. Your body also makes D3 when UVB rays from the sun hit your skin. Traditional D3 supplements are made from lanolin, a waxy substance extracted from sheep’s wool. However, a plant-based version of D3 now exists, sourced from lichen, a small organism that naturally contains the same precursor compound found in human skin. This means D3 is no longer exclusively an animal-derived vitamin.
How Much Vitamin D Is in Food
Most foods contain relatively little vitamin D on their own. Fatty fish are the standout source: a 3-ounce serving of cooked trout delivers about 645 IU, and sockeye salmon provides around 570 IU. Cod liver oil tops the list at 1,360 IU per tablespoon. These are all D3.
On the D2 side, white mushrooms exposed to UV light offer about 366 IU per half cup, which is respectable. But standard portabella mushrooms that haven’t been UV-treated provide only about 4 IU per half cup. Fortified plant milks typically contain 100 to 144 IU per cup, and fortified cereals offer around 80 IU per serving. A scrambled egg gives you 44 IU (all in the yolk), and cheddar cheese has just 17 IU per 1.5-ounce serving.
D3 Raises Blood Levels More Effectively
Both D2 and D3 are biologically inactive when you first consume them. They follow a similar activation pathway: your liver converts them into a circulating form called 25-hydroxyvitamin D (the marker your doctor measures in a blood test), and then your kidneys convert that into the fully active hormone your body uses.
The critical difference is how well each form does this job. A systematic review and meta-analysis of randomized controlled trials found that D3 supplementation raised blood levels of 25-hydroxyvitamin D significantly more than D2. The advantage was especially pronounced with larger, less frequent doses (such as a weekly or monthly bolus). Interestingly, when people took either form daily, the gap between D2 and D3 narrowed. So if you do take D2, daily dosing is likely more effective than taking it sporadically.
Part of this difference comes down to how long each form lasts in your bloodstream. The circulating form of D2 has an average half-life of about 13.9 days, while D3’s circulating form lasts about 15.1 days. That roughly one-day difference compounds over time, meaning D3 maintains steadier levels between doses.
Why Doctors Sometimes Prescribe D2
If D3 is more effective, you might wonder why D2 exists in prescription form at all. The answer is partly historical and partly practical. High-dose D2 has been available by prescription for decades, and it remains the standard option many providers reach for when treating a deficiency. D2 is also plant-derived, which made it the default for patients following vegan diets before lichen-sourced D3 became available. Over-the-counter D3 supplements are now widely accessible, but prescription-strength formulations still tend to be D2.
Choosing Between D2 and D3
For most people, D3 is the stronger option. It raises blood levels more effectively and stays in circulation slightly longer. If you eat animal products or are comfortable with a lanolin-derived supplement, standard D3 is straightforward. If you follow a vegan diet, you now have two choices: D2 from mushrooms and fortified foods, or lichen-sourced D3 supplements that are entirely plant-based and chemically identical to the D3 your skin produces.
If you’re taking D2 (whether by prescription or by preference), taking it daily rather than in a large weekly dose will help you get the most out of it. The efficacy gap between D2 and D3 is real but not dramatic with consistent daily use.
How Much You Need and Upper Limits
Regardless of which form you take, the goal is the same: maintaining adequate blood levels of 25-hydroxyvitamin D. Vitamin D toxicity is rare and generally doesn’t occur until blood levels exceed 150 ng/mL, a threshold that requires sustained intake far above normal supplementation. Clinical cases of toxicity with symptoms like elevated blood calcium have been documented at levels as high as 364 ng/mL. In practical terms, reaching toxic levels from food and moderate supplementation is extremely unlikely. The real risk for most people is getting too little, not too much.