Vitamin D, also known as calciferol, promotes calcium absorption to support bone health. It also helps reduce inflammation, keeps your immune system healthy, and plays a role in brain function. The two main forms of vitamin D are vitamin D2 and vitamin D3.
Vitamin D2 comes from plants and fortified foods, while vitamin D3 comes from sunlight when it touches the skin and animal products. While both forms can help maintain adequate vitamin D levels in the body, there are a few differences between the two.
Vitamin D is well-known for supporting bone health. Both vitamins D2 and D3 help the body absorb calcium and phosphorus, which are essential for building and maintaining strong bones.
Without enough vitamin D, bones can become brittle, thin, and soft, increasing the risk of fractures and conditions like osteoporosis. In children, a prolonged and severe vitamin D deficiency can lead to rickets, a condition that causes soft bones, delayed growth, and pain.
Vitamins D2 and D3 also play important roles in immune function, muscle strength, and the regulation and function of the nervous system.
Vitamin D2 and D3 are types of vitamin D that help maintain or raise vitamin D levels in the blood and treat deficiencies. They have slightly different chemical structures and come from different sources.
Where They’re Formed
Vitamin D2 (ergocalciferol) is primarily produced when ergosterol, a compound found in plants and fungi, is exposed to sunlight or ultraviolet (UV) light.
Vitamin D3, on the other hand, is mostly produced by the body when the skin is exposed to sunlight. This happens when UVB rays from the sun convert a substance in the skin called 7-dehydrocholesterol into vitamin D3 through a series of chemical reactions. You can also find vitamin D3 in animal products like fatty fish, egg yolks, and cheese.
How They’re Processed in the Body
Vitamin D2 and D3 are both well-absorbed in the small intestine, but they’re broken down slightly differently in the liver.
When vitamin D2 is consumed, the liver turns it into 25-hydroxyvitamin D2 (ercalcidiol), while vitamin D3 is turned into 25-hydroxyvitamin D3 (calcidiol). Together, these compounds are known as calcidiol, the main circulating form of vitamin D and what healthcare providers typically measure when testing vitamin D levels.
Calcidiol is then converted to calcitriol—the fully active form of vitamin D that the body can use—in the kidneys.
Vitamin D3 May Be More Effective at Raising Vitamin D Levels
Research shows that vitamin D3 may be more effective than vitamin D2 at raising circulating vitamin D levels in the blood. A recent review of 24 studies found that, on average, people taking vitamin D3 had 15.69 nanomoles per liter higher vitamin D levels than those taking vitamin D2.
Research also shows that vitamin D3 supplements may help maintain higher vitamin D levels for a longer period than vitamin D2.
The processing of vitamin D2 and D3 in the body can vary from person to person based on age, gender, and ethnicity. Though studies have said vitamin D3 may be more effective than vitamin D2, more research is needed to determine this definitively.
The recommended daily intake of vitamin D includes all sources of vitamin D and varies by age. It’s typically measured in international units (IU) or micrograms (mcg), and dosages aren’t broken down by vitamin D type. The recommended amount of daily vitamin D is:
| Age | Recommended Amount |
| Infants under 12 months | 400 IU (10 mcg) |
| Children 1-13 years | 600 IU (15 mcg) |
| Teens 14-18 years | 600 IU (15 mcg) |
| Adults 19-70 years | 600 IU (15 mcg) |
| Adults over age 71 | 800 IU (20 mcg) |
| Pregnant and breastfeeding people | 600 IU (15 mcg) |
Vitamin D deficiency is relatively common, affecting around 10% of people in the United States. A healthcare provider can help you figure out if you need to increase your vitamin D intake.
You can increase your vitamin D intake by eating more vitamin D-rich foods, taking supplements, and spending a few minutes in the sun several times per week. Dietary supplements are usually the most effective treatment for those diagnosed with vitamin D deficiency.
You can find vitamin D3 supplements—typically derived from lanolin (an oil from sheep’s wool)—over the counter at most supermarkets and your local pharmacy. If you’re following a vegan diet, vitamin D2 or vegan-friendly vitamin D3 supplements made from lichen (a plant-based organism made of algae and fungi) may be a good alternative.
Before taking any vitamin D supplements, you should talk to your healthcare provider to help determine which supplement is right for you and your ideal intake.
Mushrooms, especially shiitake, maitake, and oyster varieties, are among the few foods that naturally contain vitamin D2. Some mushrooms, like portobello, are treated with UV light to boost their vitamin D2 content.
You can also find sources fortified with vitamin D2. A fortified source has nutrients added to it, which in this case is vitamin D. Some vitamin D2-fortified sources include:
- Fortified milk and plant-based milk: Up to 18% Daily Value (DV) of vitamin D per cup
- Fortified breakfast cereals: Often offer around 10% DV per serving
- Fortified orange juice: Can contain as much as 25% DV per cup
- Supplements: Widely available in liquid, capsule, tablet, or pill form
Sunlight is the primary source of vitamin D3. Other sources that are also relatively high in vitamin D3 include:
- Cod liver oil: 170% Daily Value (DV) of vitamin D
- Trout: 81% DV per 3-ounce serving
- Salmon (sockeye): 71% DV per 3-ounce serving
- Eggs: 6% DV per large scrambled egg
- Beef liver: 5% DV per 3-ounce serving
- Canned tuna: 5% DV per 3-ounce serving
- Supplements: Available in liquid, capsule, tablets, and pill forms
Vitamins D2 and D3 are the two main forms of vitamin D. Vitamin D is essential for bone health, muscle strength, and overall body function. Vitamins D2 and D3 can both maintain or increase vitamin D levels, but there are some differences between them.
While vitamin D2 comes from plant sources like mushrooms, our skin produces vitamin D3 when exposed to sunlight. Vitamin D3 is also found in animal products like fish and eggs. Vitamins D2 and D3 are both available in supplement form.
Talk to your healthcare provider about whether you need to increase your vitamin D2 or D3 intake and, if so, what your best options are.
