Vitamin D from natural sources

Very few naturally occurring foods are rich in vitamin D. Typically animal foods contain cholecalciferol, while plant foods contain ergocalciferol. 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.

Liver meat is another source of abundant vitamin D. For vegetarians or vegans, all edible mushrooms have some content of vitamin D2 and ergosterol, which becomes activated with UVB exposure.

The two basic substances with vitamin D activity D2 and D3, occur only in yeast and fish liver oils. Vitamin D is also presents in small quantities in vegetables, meat and egg yolk.

The main food sources are those to which crystalline vitamin D has been added. Milk, because it is commonly used, has proved to be the most practical carrier. In United States fluid milk is voluntary fortified with 400 IU per quart of vitamin D.

The most efficient source of the vitamin D 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 provides 90 to 100% of the requirement for most people who are exposed to adequate sunlight. Vitamin D3 is synthesized in human skin from 7-dehydrocholesterol following exposure to ultraviolet B radiation with wavelength 290 to 320 nm.

Like other fat soluble vitamins, the sunlight activated pro-vitamin D can be stored away in the liver.
Vitamin D from natural sources