Vitamin D is produced by the skin upon sun exposure and works in the body to maintain proper levels of calcium and phosphorus in the bloodstream. For individuals who spend a lot of time indoors or who live in northern countries where sunlight is limited during winter months, supplemental vitamin D may be necessary. The two major forms of vitamin D available for consumption are D3 and D2.
Vitamin D3
Vitamin D3 is the specific form of vitamin D synthesized by the skin as a reaction to sun exposure. Synthetically produced vitamin D3 can be added to foods or taken in supplement form. The other main form of vitamin D, called vitamin D2, is produced by plants and yeast. Vitamin D2 can also be used for fortification or in supplements, although it may not operate as effectively in the body as D3.
Recommendations
The Food and Nutrition Board of the Institute of Medicine has set recommended dietary allowances for vitamin D taken in food or supplement form. The RDAs assume minimal sun exposure and therefore minimal skin production of vitamin D. The recommended amount for individuals between the ages of 1 and 70, including pregnant and lactating women, is 600 IU, or 15 micrograms, per day. Elderly people over the age of 70 need 800 IU, or 20 micrograms, per day. Infants under 1 year need 400 IU, or 10 micrograms, per day. Formula-fed infants typically receive this amount as long as they are consuming 27 to 32 oz. of formula a day. Breastfed infants may become deficient in vitamin D, so the American Academy of Pediatrics recommends that breastfed babies receive a supplement of 400 IU of vitamin D every day.
Toxicity
The toxicity threshold for vitamin D3 when taken in food or supplement form is between 10,000 and 40,000 IU per day, according to the Office of Dietary Supplements. The FNB has set an upper limit of 4,000 IU for individuals over 9 years old and limits between 1,000 and 3,000 for younger children.
Considerations
Obtaining vitamin D through sun exposure when possible may be a better method than taking it in supplement form. According to Medline Plus, six days of casual sun exposure can restore bodily supplies of vitamin D and make up for 49 days of zero sun exposure. The vitamin D produced upon sun exposure is stored in body fat and released during the winter and other times when sunlight is lacking. Five to 30 minutes per day of direct sun exposure -- without sunscreen -- during spring, summer and fall is generally sufficient to maintain adequate stores of this vitamin.
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