Vitamin D is found in some food sources, like fortified milk and cereals. The body also produces vitamin D during sun exposure. However, you may need extra vitamin D each day, especially if you have limited sun exposure. If you think you might be deficient in vitamin D, consult your doctor before taking supplements, since high doses can cause unwanted side effects.
Adults
The current recommended dietary allowance for most healthy adults is 600 IU, or 15 mcg per day. The National Institutes of Health defines RDA as the amount of a given nutrient that is able to meet the requirements for 97 to 98 percent of healthy people. If you take vitamin D supplements, you should limit your intake to 4,000 IU per day. Higher doses may cause high blood levels of calcium, which can lead to kidney damage and kidney stones, calcium deposits in soft tissues, nausea, vomiting and weight loss.
Children
Adequate vitamin D intake is especially important for infants and children. Human breast milk does not contain high amounts of vitamin D, so infants are at a high risk for vitamin D deficiency, which may cause rickets. Symptoms of rickets include slow growth, pain in the spine, legs and pelvis, and muscle weakness. To prevent vitamin D deficiency, doctors recommend that exclusively breastfed infants receive vitamin D supplements of 400 IU per day, which is the RDA for infants. Children older than 12 months need 600 IU, or 15 mcg per day, just like adults.
The Elderly
As you age, your body's ability to absorb vitamin D decreases. For this reason, adults over age 70 need to increase their intake of vitamin D, usually with supplementation. The National Institutes of Health recommends that adults over 70 receive 800 IU, or 20 mcg of vitamin D each day. A study by researchers from the Center on Aging and Mobility at University Hospital Zurich, Switzerland, published on the "British Medical Journal" website in October 2009 found that seniors who took between 700 and 1,000 IU of vitamin D per day were also less likely to suffer fall injuries than those who did not.
Other Groups
If you receive limited sun exposure due to your work environment or other factors, or if you have dark skin or a fat malabsorption syndrome such as Crohn's disease or cystic fibrosis, consult your doctor to discuss the right amount of vitamin D for you. You might need higher doses than most adults. You might also need to take vitamin D supplements if you are obese or if you have had recent gastric bypass surgery.
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