ergocalciferol
Meaning of ergocalciferol: Vitamin D2, produced by shining ultraviolet light on yeast or mushrooms, and the one form of vitamin D the body cannot make.
Definition of ergocalciferol
Ergocalciferol is the fungal and plant form of vitamin D, known as vitamin D2. Ultraviolet light converts ergosterol in yeast and mushrooms into it, and the same reaction is used to manufacture it in bulk. Once swallowed, it is altered first by the liver and then by the kidneys into the active hormone that lets the gut absorb calcium and phosphorus.
How does it become active?
Ergocalciferol does nothing useful in the form that is swallowed. The liver adds an oxygen atom to make 25-hydroxyvitamin D, the form measured in a blood test because it circulates in the largest amount and lasts longest. The kidneys add a second one, producing calcitriol, the active hormone. Calcitriol instructs the gut lining to absorb calcium and phosphorus from food, and works with parathyroid hormone to hold the blood level steady. Without it, absorption falls and bone pays the price.
How does it differ from vitamin D3?
| Ergocalciferol, D2 | Cholecalciferol, D3 | |
|---|---|---|
| Source | Yeast and mushrooms exposed to ultraviolet light | Oily fish, egg yolk, and human skin in sunlight |
| Made in the human body | No | Yes, from a cholesterol relative in skin |
| Suits a vegan diet | Yes | Only the lichen derived form |
| Effect on blood level | Raises it, though less durably in most comparisons | Raises it and holds it longer |
Both pass through the same liver and kidney steps, and both count as vitamin D on a label.
Why does fat soluble matter?
Ergocalciferol dissolves in fat rather than water, and that has two consequences. It is absorbed alongside dietary fat, so conditions that impair fat absorption, such as celiac disease or surgery that shortens the bowel, reduce how much gets in. It is also stored in fat tissue and the liver instead of being flushed out in urine, so a heavy intake accumulates. That is the opposite of a water soluble vitamin, where a surplus is largely excreted. Excess vitamin D taken as a dietary supplement raises blood calcium and can injure the kidneys, an effect that sunlight and ordinary food do not produce.
Also known as
Used in a sentence
The record noted ergocalciferol supplementation after blood testing showed vitamin D deficiency.
Good to know
Human skin cannot make ergocalciferol, producing cholecalciferol instead, and because vitamin D is stored in fat rather than excreted, a large sustained intake accumulates and can raise blood calcium.
Word origin
Where “ergocalciferol” comes from
The name joins ergosterol, the fungal sterol it is made from, with calciferol, from the Latin calx, meaning lime, and ferre, meaning to carry.