Vitamin D is a fat-soluble vitamin and a sterol derivative. There are many kinds of known vitamin D, the more important ones are vitamin D2 and D3, their structures are very similar, but the side chains are different. Vitamin D is a colorless crystal, soluble in fat, fat solvent and organic solvent, chemically stable, heat-resistant in neutral and alkaline solutions, not easily oxidized, but gradually decomposed in acidic solutions.
