Some food items that naturally contain small amounts of vitamin D include oil fish such as salmon, mackerel and blue fish. Cod liver oil is the best source of vitamin D.
The two basic substances with vitamin D activity D2 and D3, occur only in yeast and fish liver oils.
Vitamin D is also present in small quantities in vegetables, meat and egg yolk.
The main food source are those to which crystalline vitamin D has been added. Milk, because it is commonly used, has prove to be the most practical carrier.
The most efficient source of the vitamin is not a food at all, but exposure to sunlight, which transforms a related pro-vitamin substance in the skin into a substance which the kidney can change into active vitamin D.
Sunlight, in the form of ultraviolet-B radiation, providing 90-100% of the requirement for most people who are exposed to adequate sunlight.
Like other fat soluble vitamins, the sunlight activated pro-vitamin D can be stored away in the liver.
Vitamin D can also be obtained from nutritional supplements, For example, multivitamin supplements typically contain 400 IU vitamin D and pharmaceutical preparations can contain as much as 50,000 IU vitamin D per capsule/tablet.
Natural Sources of Vitamin D