Vitamin D3 5000 IU from Doctor's Best® features 5,000 IU (125 mcg) of cholecalciferol per softgel. Cholecalciferol is derived from lanolin, which is a component of sheep's wool. Vitamin D3 is known to interact with over 200 different genes and thus plays a crucial regulatory role as a metabolic activator for a multitude of metabolic processes.