Sources of Vitamin D2

A group of five fat-soluble molecules called secosteroids are collectively known as vitamin D. Vitamin D3, or cholecalciferal, is the type produced by skin in response to sunlight's ultraviolet-B component. Vitamin D2, or ergocalciferol, is obtained exclusively from dietary sources or supplementation. Vitamin D's crucial role in human health is becoming better appreciated, but unfortunately as a 2009 article in "Scientific American" outlines, up to 75 percent of U.S. teens and adults are deficient in vitamin D.

Animal Sources

Very few natural foods contain vitamin D, making it difficult to attain recommended levels without sunlight exposure. According to the National Institutes of Health, the flesh of fish, especially salmon, mackerel, sardines, cod and tuna are the best food sources of vitamin D in general, although the D3 form is more prevalent in these foods. Fish oils, such as cod liver oil, are also very rich in both vitamins D2 and D3. Smaller amounts of vitamin D2 are found in beef liver, shrimp, Swiss cheese and egg yolks.

Enhanced Mushrooms

Some mushrooms provide vitamin D2 in variable amounts. Mushrooms are exposed to ultraviolet light under controlled conditions to artificially induce levels of vitamin D2, however, they are not commonly available at this time.

Fortified Foods

Fortified foods provide most of the vitamin D in the American diet according to the National Institutes of Health. Mush of the U.S. milk supply is fortified with vitamins D2 and D3. Other dairy products made from milk are generally not fortified. Breakfast cereals often contain added vitamin D, as do some brands of orange juice, yogurt and margarine. By U.S. law, the only foods allowed to be fortified with vitamin D are cereal flours and related products, milk and milk products, and calcium-fortified fruit juices and drinks.

Supplementation

The two forms of vitamin D used in dietary supplements are D2 and D3. Vitamin D2 is usually considered a vegetarian source of vitamin D since it's often plant-derived, but yeast and fungi are also used as sources, which some consider animal-based. Most researchers consider vitamin D3 a far better form for supplementation than vitamin D2. In fact, a 2006 article in the "American Journal of Clinical Nutrition" argued that D2 should no longer be considered suitable for fortification or supplementation because D3 had such strong hormonal advantages.

The U.S. Department of Agriculture recommends 200 IU of vitamin D per day for adults up to 50 years of age. This is a level meant to avoid acute deficiency, not optimize health. Higher daily levels are needed for optimal health, although there is debate over appropriate amounts. Many researchers believe that between 1,000 and 2,000 IU per day for adults is more beneficial.