Vitamin D, also known as calciferol, promotes calcium absorption to support bone health. It also helps reduce inflammation, keeping 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. Although both forms can help maintain adequate levels of vitamin D in the body, there are several differences between them.
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, 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 nervous system regulation and function.
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 a slightly different chemical structure and come from different sources.
Where they were 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 mainly produced by the body when the skin is exposed to sunlight. This happens when the sun’s UVB rays 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 such as fatty fish, egg yolks and cheese.
How they are processed in the body
Vitamin D2 and D3 are well absorbed in the small intestine, but are broken down slightly differently in the liver.
When vitamin D2 is consumed, the liver converts it to 25-hydroxyvitamin D2 (ercalcidiol), while vitamin D3 is converted to 25-hydroxyvitamin D3 (calcidiol). Together, these compounds are known as calcidiol, the main circulating form of vitamin D and what health professionals usually 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 in raising vitamin D levels
Research shows that vitamin D3 may be more effective than vitamin D2 in raising vitamin D levels in the blood. A recent review of 24 studies found that people taking vitamin D3 had an average of 15.69 nanomoles per liter higher vitamin D levels than those taking vitamin D2.
Research also shows that vitamin D3 supplements can help maintain higher vitamin D levels for a longer period of time than vitamin D2.
The processing of vitamin D2 and D3 in the body can vary from person to person depending on age, gender and ethnicity. Although studies suggest that 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 is usually measured in international units (IU) or micrograms (mcg), and doses are not broken down by type of vitamin D. The recommended daily amount of vitamin D is:
| Old age | Recommended amount |
| Children under 12 months | 400 IU (10 mcg) |
| Children 1-13 years | 600 IU (15 mcg) |
| Teenagers 14-18 years | 600 IU (15 mcg) |
| Adults 19-70 years old | 600 IU (15 mcg) |
| Adults over 71 years old | 800 IU (20 mcg) |
| Pregnant and lactating women | 600 IU (15 mcg) |
Vitamin D deficiency is relatively common, affecting about 10% of people in the United States. Your doctor can help you determine 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 a few times a week. Dietary supplements are usually the most effective treatment for those diagnosed with vitamin D deficiency.
You can find vitamin D3 supplements — usually derived from lanolin (sheep’s wool oil) — over the counter in most supermarkets and at your local pharmacy. If you follow a vegan diet, vitamin D2 or vegan-friendly vitamin D3 supplements made from lichen (a plant organism made from algae and fungi) may be a good alternative.
Before taking any vitamin D supplement, you should talk to your doctor to help you determine which supplement is right for you and your ideal intake.
Mushrooms, especially shiitake, maitake and oyster, are among the rare foods that naturally contain vitamin D2. Some mushrooms, such as portobello, are treated with UV light to increase their vitamin D2 content.
You can also find sources fortified with vitamin D2. A fortified source has nutrients added to it, in this case vitamin D. Some sources fortified with vitamin D2 include:
- Fortified milk and plant-based milk: Up to 18% of the daily value (DV) of vitamin D per cup
- Fortified breakfast cereals: They often offer about 10% DV per serving
- Fortified orange juice: It can contain as much as 25% DV per cup
- Extras: 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% of the 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
- Extras: Available in liquid, capsule, tablet and pill form
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 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 such as fish and eggs. Vitamins D2 and D3 are available in supplement form.
Talk to your doctor about whether you should increase your vitamin D2 or D3 intake and, if so, what your best options are.
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