Vitamin D3, also known as cholecalciferol, is an active form of vitamin D, a fat-soluble vitamin that plays an integral role in normal calcium balance and bone remodeling. Sunlight catalyzes the conversion of cholesterol into vitamin D in the skin. When sun exposure does not synthesize adequate amounts, vitamin D must be obtained from dietary sources. The recommended daily intake, according to the Institute of Medicine, is 15 mcg, or 600 IU, for adults.
Sunlight
The best source of vitamin D3 is ultraviolet B radiation from the sun, which stimulates synthesis in the skin's outer layer. While the degree of synthesis varies according to several factors, sufficient exposure can provide people with their entire daily requirement. Dr. Michael Holick, a leading researcher on Vitamin D, recommends as little as 5 to 10 minutes of exposure on the face or extremities three times weekly between the hours of 11 a.m. and 2 p.m. during the spring, summer and fall. This will provide adequate vitamin D as well as allow for storage for winter months.
Fatty Fish
Vitamin D3 is naturally present in very few foods. The best dietary source is fatty fish, including mackerel, salmon, tuna and sardines. Three ounces of canned pink salmon, sardines or mackerel offer 530 IU, 231 IU and 213 IU, respectively. Canned tuna provides 154 IU. Vitamin D is also found in fish liver oils; 1 tbsp. contains 1,360 IU.
Dairy
Fortified foods provide most of the vitamin D in the American diet. Milk and infant formula are fortified with vitamin D to contain 400 IU, or 10 mcg, per quart. Soy milk is occasionally fortified with vitamin D to provide 100 IU per cup. Other dairy products, such as cheese and yogurt, are not usually fortified.
Grains
Occasionally, some ready-to-eat cereals and breads are fortified with vitamin D. One serving of fortified cereal, which is about one cup, typically contains 40 to 50 IU of vitamin D.
Other Foods
Eggs that come from chickens who were fed vitamin D will also contain some vitamin D. One large yolk contains 21 to 41 IU. Orange juice is another beverage that is sometimes fortified with vitamin D -- a cup usually has about 100 IU of the vitamin. Beef liver also contains small amounts of vitamin D, at about 49 IU in 3.5 oz.
Supplements
Supplements are another good source of vitamin D3, especially for those with a deficiency. Multivitamins generally provide around 400 IU of vitamin D, but supplements only containing vitamin D can have anywhere from 400 to 2,000 IU. Higher doses, up to 50,000 IU, require a doctor's prescription. Some calcium supplements might also contain vitamin D.
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