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.
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.
| Vitamin D2 | Vitamin D3 |
| Naturally produced by invertebrates, like fungus and plants, when exposed to the sun. | Naturally produced in the skin of all vertebrates when exposed to sun. |
| Lab created for human consumption in supplement form by exposing fungus to ultra violet light. | Lab created for human consumption in supplement form by exposing wool grease to ultra violet light. |
| Aids in calcium absorption, regulates phosphorous. | Aids in calcium absorption, strengthens bones, regulates phosphorous, prevents rickets and adult osteomalacia. |
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.
Humans need between 10 and 60 minutes spent in the sun allows the body to create enough vitamin D3 for an entire day. However, the skin cannot produce D3 in sunlight that’s filtered through a window, or on cloudy days.
For consumption, a healthy adult needs to eat 600 International Units of vitamin D per day.
