Vitamin D is a fat-soluble vitamin, meaning that it dissolves in fat rather than in water. Because vitamin D is carried through the body by fat and stored in fat tissue instead of being excreted from the body, getting too much can be harmful. Vitamin D can be produced in the body, as well as obtained from the diet.
What food source is the nutrient found in?
The most reliable source of vitamin D, in the American diet, is fortified milk
. All milk sold in the United States is fortified with vitamin D. Vitamin D is also present in:
- some soy milks
- fish such as sardines and salmon
- cod liver oil
- fortified cereals
Vitamin D is called the sunshine vitamin. This is because the body can make vitamin D after sunlight, or ultraviolet light, hits the skin. Ten to 15 minutes of sun exposure 3 times a week (generally not enough to put a person at risk for skin damage) is all the body needs. Older people are less efficient with this conversion.
How does the nutrient affect the body?
Vitamin D helps build strong and healthy bones and teeth. It does this by helping the body to absorb the minerals calcium and phosphorous and to deposit them in bones and teeth.
If the body does not get enough vitamin D and calcium, a person is at higher risk for bone mass loss, which is known as osteoporosis. Low levels of vitamin D also increases the risk of bone softening, known as osteomalacia, in older adults. Children who do not get enough vitamin D over a long period may develop rickets, which is defective bone growth. Fortifying milk with vitamin D has made rickets extremely rare in the US.
Vitamin D is measured as micrograms (mcg) of cholecalciferol (koh-li-kal-sif-ah-rall). The "Adequate Intake" (AI), because no official Recommended Dietary Allowance (RDA) has been established, for males and females up through age 50 is 5 mcg per day. The requirement is the same for pregnant or breastfeeding women. For those 50-70 years of age, 10 mcg is recommended, and for 71 years of age and over, 15 mcg. Sometimes vitamin D is measured in "international units" (IU). One microgram is equal to 40 IU's.
No one should have more than 2000 IU (50 mcg) per day of Vitamin D. Because vitamin D dissolves in fat, it can build up in the fat tissues of the body. This can pose a problem for people taking high doses of vitamin D. While it is almost impossible to get too much vitamin D from foods or sunlight, it is easy to get too much from supplements.
High doses of vitamin D can be toxic and cause:
kidney stones or damage
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Mahan, K, MS, RD, CDE&Escott-Stump, S., MA, RD, LDN. (2000). Krause's Food, Nutrition,&Diet Therapy (10th ed.). Pennsylvania: W.B. Saunders Company.