Why do I need vitamin D?
Vitamin D -- also called the sunshine vitamin because your body makes it naturally when exposed to sunlight -- is perhaps best known for its ability to help build strong bones. Children with a serious shortfall of vitamin D can develop rickets, a condition that deforms growing bones.
But even if you get enough vitamin D to avoid rickets, you may not have enough for optimum health. Experts believe that people who don't get plenty of the vitamin may be at risk for heart disease and certain types of cancer, among other illnesses. In 2010, separate studies suggested that not getting enough D could worsen Crohn's disease and asthma -- just two examples of the far-reaching effects of this nutrient.
How much should I be getting?
According to the most recent government recommendations, everyone under the age of 50 should get at least 200 IU of vitamin D each day, and that includes women who are pregnant or breast-feeding. People between the ages of 51 and 70 should shoot for 400 IU. At age 70, the recommendation increases to 600 IU. But many experts believe that these recommendations are inadequate, especially for people who don't get enough sunlight to make much vitamin D naturally or those who may be at risk for osteoporosis. The National Osteoporosis Foundation recommends that postmenopausal women and men over the age of 50 get 800 to 1,000 IU every day.
What are good sources of Vitamin D?
People can make plenty of vitamin D on their own just by getting 10 to 15 minutes of direct sun on their face and hands (without sunscreen) three times a week. But people with dark skin and people who live in northern latitudes have a hard time soaking in enough sun to get enough D on their own. (Intriguingly, some cancers such as prostate cancer and colorectal cancer are especially common in dark-skinned people and people who live in the northern part of the country.)
For those who don't get enough sunlight, fortified milk is an excellent source of vitamin D. (In fact, the incidence of rickets dropped dramatically once the government required the addition of vitamin D in milk.) A typical glass of milk has about 100 IU of vitamin D. Other food sources include fatty fishes (almost 800 IU for a three-ounce serving of salmon, for instance), fortified orange juice (100 IU per cup), and fortified cereals (about 40 IU per serving).
Do I need a supplement?
Supplements can be a good idea if you're not getting enough sunlight or if you don't get much D in your daily diet. Most multivitamins contain 400 IU of D. A typical calcium+D supplement will have about 200 IU.
Can I get too much?
It is possible to get too much D, but it's not easy. According to the National Institutes of Health, adults can get up to 2,000 IU a day without any side effects. Go higher than that, and there's a chance that you could experience signs of Vitamin D toxicity including nausea, vomiting, and weakness. In extreme cases, an overload of D can cause confusion, irregular heartbeats, and kidney stones.
National Osteoporosis Foundation. Vitamin D and bone health. 2010. http://www.nof.org/aboutosteoporosis/prevention/vitamind
National Jewish Health. Low vitamin D associated with worse asthma. 2010. http://www.nationaljewish.org/about/mediacenter/pressreleases/2010/vitamin-d-asthma.aspx
Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. 2009. http://ods.od.nih.gov/factsheets/vitamind.asp
American Academy of Pediatrics. Vitamin D Deficiency Clinical Report. 2009 http://www.aap.org/family/vitdpatients.htm
Gartner LM, et al. Prevention of Rickets and Vitamin D Deficiency: New Guidelines for Vitamin D Intake. American Academy of Pediatrics Clinical Report. Pediatrics.Volume 111, Number 4, April 2003, pp 908-910.