"Ergosterol (ergosta-5,7,22-trien-3β-ol) is a sterol found in fungi, and named for ergot, a
common name for the members of the fungal genus Clavicepsfrom which ergosterol was first isolated. Ergosterol does not occur in plant or animal cells. It is a component of yeast and fungal cell membranes, serving the same function that cholesterol serves in animal cells."
"Ergosterol is a biological precursor (a provitamin) to vitamin D2. It is turned into viosterol by ultraviolet light, and is then converted into ergocalciferol, a form of vitamin D also known as D2 or D2.[1] For this reason, when yeast (such as brewer's yeast) and fungi (such as mushrooms), are exposed to ultraviolet light, significant amounts of vitamin D2 are produced."
"Ergosterol powder is an irritant to skin, eyes, and the respiratory tract. Ingestion of large amounts can cause hypercalcemia, which (if prolonged) can lead to calcium salt deposits in the soft tissues and, in particular, the kidneys."