Vitamin D, the sunshine vitamin, is required to facilitate the absorption of calcium at the gut level and regulate blood calcium and phosphorus concentration. Moreover, studies have shown that vitamin D can affect over 2,000 genes and could help prevent some cancers, cardiovascular disease, stroke, diabetes, depression and osteoporosis. Milk sold in the U.S. is fortified with vitamin D.
Forms of Vitamin D
Vitamin D is found in two forms--vitamin D2 and vitamin D3. Vitamin D2, or ergocalciferol, is obtained by exposing yeast to UV radiations and is also found in some mushrooms. Vitamin D3, or cholecalciferol, is the natural form produced in animals and humans, either from cholesterol or synthesized after exposure to the sun. Vitamin D3 is at least three time more effective at raising blood vitamin D levels compared to vitamin D2.
Vitamin D3
Vitamin D3 can be synthesized after exposure to UV radiation. The sun helps convert 7-dehydrocholesterol to previtamin D3, which is then transformed to the active form of vitamin D3. People living above 42 degrees north latitude--above the line between the northern extremity of California and Boston--are not able to synthesize vitamin D from November through February. Vitamin D3 can also be obtained from the food supply, especially in animal products such as saltwater fish and fish liver oils and to a smaller extent in eggs, beef, cheese, yogurt and butter. Some margarine and cereals are fortified with vitamin D3, but in the U.S., fortified fluid milk is the main source of vitamin D.
Natural Vitamin D3 in Milk
A small portion, about 50 to 80 IU per quart, of the vitamin D in milk comes from the vitamin D produced photochemically when the cow is exposed to sunlight. Some of the vitamin D produced by the cow goes into the milk produced. Milk of all mammals, even humans, is a natural source of vitamin D3.
Added Vitamin D3 in Milk
The remaining of the vitamin D content of the milk, 320 to 350 IU per quart, comes from the fortification process. Vitamin D3 can be produced chemically. First, 7-dehydrocholesterol is extracted from animal skins--usually cow, hog or sheep. After purification and dissolution in a solvent, the 7-dehydrocholesterol is irradiated with UV light to form vitamin D3. It is impossible to determine the origin of the vitamin D3 in milk. Natural or added, it has the same molecular structure. Moreover, it is also impossible to determine the animal source for the chemically synthesized vitamin D3. F. Hoffman La Roche of Switzerland and BASF of Germany, are the main companies providing vitamin D3 for milk fortification.
Vitamin D Recommendations
Adults up to 50 years old require 5 mcg or 200 IU, and adults between 51 and 70 need 10 mcg or 400 IU. Adults over the age of 70 require 15 mcg or 600 IU. Vitamin D can be synthesized from UV rays or obtained through diet. Fifteen minutes of sunshine three times a week is all that is required to meet your vitamin D requirements, except during the winter in the northern part of the U.S. However, if you prefer to err on the side of caution and limit your sun exposure to reduce your risk of developing skin cancer, milk can help you obtain your vitamin D--a cup of milk provides around 100 IU.
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