Vitamin D refers to several different but related forms of the vitamin including D2, also known as ergocalciferol, and D3, called cholecalciferol. Because few foods naturally contain vitamin D, food manufacturers fortify foods with either D2 -- a form produced by plants -- or D3 -- the form produced in your body. Your body absorbs some vitamin D from foods, but it also produces vitamin D when exposed to sunlight.
Vitamin D Function
Vitamin D regulates the amount of minerals, including calcium and phosphorus, in your blood. Because your body needs calcium and phosphorus to build new bone tissue to keep bones strong, vitamin D is vital to maintaining healthy bones. If your body cannot absorb or produce enough vitamin D, the amount of calcium decreases leaving bones weak and vulnerable to fracture.
Recommended Amount
There is no set amount of how much vitamin D your body can absorb at one time, but National Institutes of Health Office of Dietary Supplements recommends adults ages 19 to 70 years get 15 mcg, or 600 IU of vitamin D per day. Because adults over the age of 70 have an increased risk for developing weak bones, they need 20 mcg or 800 IU per day to support healthy bones.
Food Sources
Not many foods naturally contain vitamin D. Fatty fish and the oils from those fish, including mackerel, salmon and sardines, contain some vitamin D. Egg yolks also contain some vitamin D, approximately 0.53 mcg per egg. To help reduce the incidence of vitamin D deficiency, food manufactures fortify foods like milk, yogurt, breakfast cereals and orange juice with vitamin D. Although the amount of vitamin D your body absorbs at one time remains unknown, consuming foods that contain vitamin D and getting exposure to sunlight helps ensure you meet the daily recommended intake.
Production
The ultraviolet B rays from the sun stimulate your skin cells to convert previtamin D3 into vitamin D3. The amount of vitamin D3 your body can produce each day depends upon many factors; the length of time of the sun exposure, the cloud cover and the use of sun screens all affect vitamin D production. The National Institutes of Health Office of Dietary Supplements recommends you get 5 to 30 minutes of sun exposure between the times of 10 a.m. and 3 p.m. at least twice a week to produce enough vitamin D to support healthy bones.
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