It is only sparingly soluble in water but soluble in oils, fats and solutions of the bile salts. The main commerical source has been from the spinal cord of beetle cattle. It is used, together with synthetic analogues, in treating disorders due to impaired production of the natural hormone. Testosterone can be prepared commerically from dehroepiandrosterone. They are necessary for the absorption of Ca and P from the gut.
Sunlight activates the metabolism of vitamin D in the body.
The first vitamin D to be discovered was a crude mixture called vitamin D1. Irradiation of erggoterol with u.v. light gives calciferol or vitamin D2. Irradiation of 7-dehydrocholesterol gives the natural vitamin D or vitamin D2, which differs in the structure only in the side chain. Good sources of vitamin D are butter, margarine, cheese cream, yogurt, milk eggs and sunlight. It is soluble in fats, milk, butter and eggs.