Sources of Vitamin D
It is practical to consider the natural and synthetic sources of the antirachitic vitamins at this time, since interesting differences in regard to animal vitamin D (activated 7-dehydrocholesterol) and plant vitamin D (calciferol) content of the different substances arise. At present many commercial vitamin D products are available in concentrated form. Calciferol dissolved in vegetable oil or in propylene glycol is marketed for use primarily in infant and child feeding. High-potency capsules (100,000 units for instance) are also available. These preparations contain vitamin D2. Vitamin D milk is widely distributed in the United States. Practically all the evaporated milk is fortified with concentrates to increase the vitamin D content.
Either D2 or Da may be used. Fluid milk is now generally fortified with concentrates (Da primarily), although some years ago direct irradiation was employed (Da). Irradiated yeast (D2) is a high-potency product. It is used as such to some extent in human and more in animal nutrition. When it is fed to cows, a part of the vitamin D is transferred to the milk. Cod liver oil is a popular source of vitamin D (Da) for infant and child feeding. Many other types of preparations, some containing D2 and some Da' are also marketed. Naturally occurring foods have practically no vitamin D activity.
Milk contains insignificant amounts as far as infant and child nutrition is concerned unless vitamin D is added. Grains and vegetables in general have still less. Butter and liver have small quantities. It is interesting that, in contrast to many fish livers, this organ in mammals is not considered a source of the vitamin in nutrition. Reference to the discussion of vitamin A shows the vitamin D content of a number of fish liver oils.
