Your body needs vitamin D primarily to help strengthen bones and absorb calcium. Vitamin D is a fat-soluble vitamin, so your body can store it in its tissues. Any time your skin is exposed to sunlight, your body can manufacture its own vitamin D. Plants can also make their own vitamin D using sunlight. You can find both types in a number of natural and fortified dietary sources.
Vitamin D-3
Vitamin D-3, or cholacalciferol, is the natural version your body manufactures when exposed to the sun's ultraviolet rays. When exposed to the sun, the skin produces up to 20,00 thousands of units of cholacalciferol, which is then converted by the liver into a chemical that helps to maintain adequate blood calcium levels. Animals also produce cholacalciferol in their skin and fur. You can find vitamin D-3 in many animal products such as meat, milk and eggs, as well is in supplement form.
Vitamin D-2
Vitamin D-2, or ergocalciferol, is synthesized by plants. As human skin uses to ultraviolet rays to produce vitamin D-2, plants use ultraviolet rays to convert natural sterols into vitamin D-2. You can find vitamin D-2 naturally in plant sources and oils, and vitamin D-2 is commonly used to fortify foods, especially milk.
Dosage
Both vitamin D-3 and vitamin D-2 can be used to satisfy your vitamin D needs, although vitamin D-3 may be more effective at raising vitamin D levels in the bloodstream. The Food and Nutrition Board of the Institute of Medicine sets recommended daily allowances for all vitamins, and males and females over the age of 14 need about 15 mg of vitamin D per day. The IOM's RDA for vitamin D are based on the assumption that you are receiving at least a minimal amount of daily sunlight.
Highest Sources
The most abundant sources of vitamin D are fish and seafood such as salmon, cod, rockfish and tuna. Mixed chocolate drinks, milk and cereals that have been fortified with vitamin D-2 can also provide a high dose of vitamin D to your diet. Mushrooms contain among the highest natural doses of vitamin D-2.
References
- University of Maryland Medical Center: Vitamin D; June 2010
- MayoClinic.com: Vitamin D; December 2010
- Institute of Medicine; Dietary Reference Intakes; Recommended Dietary Allowances and Adequate Intakes; Vitamins; 2005
- Vitamin D Council: Vitamin D Physiology; John Jacob Cannell; June 2006
- USDA National Nutrient Database for Standard Reference; September 2010
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