There are two major forms of vitamin D — vitamin D2 and vitamin D3.
While both forms can help you meet your vitamin D needs, you may wonder how they differ.
This article explains the differences between vitamin D2 and D3, and whether one form is better than the other.
What is vitamin D?
While classified as a vitamin, vitamin D is more of a hormone.
More than 30 organs, including the bones, intestine, kidneys, muscles, and skin, have vitamin D receptors (1).
Vitamin D binds to these receptors to exert a range of functions related to bone health, blood sugar control, blood pressure regulation as well as immune and muscle function (2).
Vitamin D is unique because your skin can make it from sunlight, which is why it’s commonly referred to as the “sunshine vitamin.”
Approximately five to 30 minutes of sun exposure (without sunscreen) between 10 AM and 3 PM at least twice per week can provide enough vitamin D (3).
Several factors, however, can affect vitamin D production from sun exposure.
For example, people with a darker skin tone require three to five times longer sun exposure to make the same amount of vitamin D as a person with a white skin tone (4).
Vitamin D2 vs D3
The two main forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
Vitamin D3 is the form of vitamin D that is made in the skin from sunlight.
This form is also naturally found in some animal-based foods, including beef liver, egg yolks, and fatty fish like salmon and tuna.
Fungi, such as yeast and mushrooms, produce vitamin D2 using sunlight (5).
Some mushrooms sold in stores have been intentionally exposed to ultraviolet light during farming to increase their vitamin D content (6).
Because there are few natural dietary sources of vitamin D, many commonly consumed foods are fortified with the vitamin — either as vitamin D2 or D3.
In fact, fortified foods provide most of the vitamin D in American’s diets (7).
Foods commonly fortified with vitamin D include orange juice, breakfast cereals, yogurt, milk, and dairy alternatives like soy and almond milk.
Vitamin D2 and D3 are also sold as dietary supplements.
Effects of vitamin D2 and D3 on vitamin D levels
While both vitamin D2 and D3 can increase blood levels of vitamin D, a review of seven randomized clinical trials demonstrated that vitamin D3 was more effective than vitamin D2 (8).
When the studies were analyzed by their dosing regimen, however, vitamin D3 was shown to be better than D2 only when supplemented in large doses separated by weeks or months.
No significant differences between daily vitamin D2 and D3 supplementation on vitamin D levels were found.
Similarly, the results of another study demonstrated that the effects of vitamin D2 and D3 supplements on vitamin D levels may be dependent on the dosing (9).
The results showed that vitamin D3 was less effective than vitamin D2 at raising vitamin D levels when supplemented with daily in smaller doses but more effective when supplemented two to four times per week in larger doses.
Collectively, these results suggest that vitamin D3 may be more effective at raising and maintaining levels of vitamin D when supplemented with in less frequent, larger doses, whereas vitamin D2 may be best taken daily in smaller amounts.
How much vitamin D do you need?
The daily recommended amounts for vitamin D varies depending on age (7):
- 0-12 months: 400 international units (IU) or 10 micrograms (mcg)
- 1-70 years: 600 IU or 15 mcg
- >70 years: 800 IU or 20 mcg
These recommendations were established on the basis of minimal sun exposure, and should be enough to maintain adequate vitamin D levels in the blood.
The best indicator of vitamin D status is the blood concentration of 25-hydroxyvitamin D [25(OH)D], also known as calcidiol.
The National Academy of Sciences considers a 25(OH)D level of 20 nanograms per milliliter (ng/mL) or 50 nanomoles per liter (nmol/L) adequate.
Other research, however, suggests that the current vitamin D recommendations are too low.
The study reported that 1,044 IU was required to maintain adequate 25(OH)D levels.
Scientific organizations, like the Endocrine Society, agree that the current recommendations may be too low, suggesting that adults aged 19 and older require at least 1,500 to 2,000 IU of vitamin D per day (11).
Certain populations, such as older adults, people who are obese, or those who have intestinal malabsorption disorders, like celiac disease and cystic fibrosis, may require more vitamin D to meet their needs (12, 13, 14).
The bottom line
There are two forms of vitamin D — D2 and D3.
Vitamin D3 is the form made in your skin from sun exposure. It’s also found naturally in some animal-based foods.
On the other hand, vitamin D2 is naturally made from fungi using sunlight.
Both forms of vitamin D are used to fortify foods and are sold as dietary supplements.
Vitamin D3 may be more effective in larger, less frequent doses, whereas vitamin D2 may be better in smaller, daily doses.