“Vitamin D” (calciferol) is considered to be a beneficial and necessary nutrient, but there is no single vitamin called "vitamin D". What we know as vitamin D is essentially a collective term for two types of calciferol: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is made in the skin of all vertebrates when exposed to sun, while D2 is produced by invertebrates, like fungus and plants, when exposed to the sun.

Generally, the word “vitamin” refers to a substance that the human body cannot produce on its own. So even though it has always been known as a vitamin and an essential one, vitamin D3 is technically not a vitamin but a hormone.

Comparison chart

Vitamin D2 versus Vitamin D3 comparison chart
Edit this comparison chartVitamin D2Vitamin D3
Form Ergocalciferol Cholecalciferol or calciol
Origin Made in plants and fungus exposed to ultra violet light; synthesized in laboratories Made in skin of vertebrates when exposed to sunlight.
Benefits Aids in calcium absorption, regulates phosphorous. Aids in calcium absorption, strengthens bones, regulates phosphorous, prevents rickets and adult osteomalacia.
Year discovered 1914 1925
Melting point 114-118 °C 83–86 °C
Molecular formula C28H44O C27H44O
Molar mass 396.65 g/mol 384.64 g/mol
UNII VS041H42XC Y 1C6V77QF41 Y
CAS number 50-14-6 Y 67-97-0 Y= Y
ChemSpider 4444351 Y 9058792 Y

How D2 and D3 are Formed

When in contact with the sun, human skin has the ability to generate vitamin D3, which generally satisfies all its beneficial requirements. However, the skin cannot produce D3 in sunlight that's filtered through a window, or on cloudy days.

Invertebrates like plants and fungus produce vitamin D2 in much the same way as the human skin produces D3. However, vitamin D2 made for human consumption in supplement form is created in a laboratory by exposing fungus to ultra violet light.


Humans can absorb D3 through the sun, but also by eating animal products. There are small amounts of D3 – plus other nutrients – in foods such and fish and eggs that the body can use.

Humans can get D2 in synthetic pill or supplement form, or by consuming plant products.


As little as 10 minutes spent in the sun can allow the body to create enough vitamin D3 for an entire day.

For consumption, a healthy adult needs to eat 600 International Units of vitamin D per day. For reference, a quart of milk provides about 400 IU of vitamin D.

Are D2 and D3 Equal as Vitamins?

Initially, it was thought that D3 and D2 were equivalent. However, some nutritionists and food scientists theorize that D2 is less effective than D3.

Some experts say that D2 does not get absorbed into the bloodstream well and has a short shelf life.

Health benefits of Vitamin D

Despite debate over the efficacy of D2, experts say that vitamin D in general is a necessary nutrient with multiple health benefits.

Other Uses

Ergosterol found in viatmind D2 can efficiently absorb the ultraviolet radiation that can damage DNA, RNA and protein in the body. Natural ergosterol serves as a sunscreening system that protects organisms from damaging high energy ultraviolet radiation. Ergosterol obtained in laboratories is used in making sunscreen and sun protecting creams.


A lack of vitamin D can cause rickets, a bone softening disease in children.

Most studies point to vitamin D as necessary not because it provides extra health benefits, but because a deficiency of vitamin D can lead to osteomalacia in adults, a painful bone disorder.

Structural Differences

The structural difference between vitamin D2 and vitamin D3 is in their side chains. The side chain of D2 contains a double bond between carbons 22 and 23, and a methyl group on carbon 24.

Vitamin D2 (made from ergosterol) is produced by invertebrates, fungus and plants in response to UV irradiation.

Vitamin D3 is made in the skin when 7-dehydrocholesterol reacts with UVB ultraviolet light at wavelengths between 270–300 nm, with peak synthesis occurring between 295–297 nm. These wavelengths are present in sunlight when the UV index is greater than 3 and also in the light emitted by the UV lamps in tanning beds. At this solar elevation, which occurs daily within the tropics, daily during the spring and summer seasons in temperate regions, and almost never within the arctic circles, vitamin D3 can be made in the skin.


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