Vitamin D grabs calcium and phosphorus out of your intestines and dumps them into your bloodstream where they can be absorbed by your bones and keep your skeleton strong. Children who get too little D can develop rickets, a bone deforming condition that can lead to bowlegs and knock-knees. In adults, a D shortage can contribute to osteoporosis, the "brittle bones" disease, and bring on pain in the bones and joints. (The symptoms are sometimes misdiagnosed as arthritis.) Vitamin D also seems to protect the body from different cancers. Sixty years of study show that vitamin D has an inverse relationship to cancer, though most of this research has focused on colon and colorectal cancer. More encouraging, a 2005 study has found that taking 1,000 IU daily of vitamin D3 cuts the risk of other cancers -- including breast and ovarian cancer -- by up to 50 percent.

According to the most recent government recommendations, you need 200 IU a day until you reach age 50, even if you're pregnant or breast-feeding. If you're between ages 51 and 70, you need 400 IU; if over age 70, you need 600 IU. However experts believe you need more than the government's recommendation, especially if you are at risk of not getting enough vitamin D. The National Osteoporosis Foundation recommends getting 800 to 1,000 IU daily for postmenopausal women and men over the age of 50.

Your body can actually manufacture D on its own (with a little help from the sun); technically, that makes it a hormone, not a vitamin. With 10 to 15 minutes of direct sunshine on your hands and face three times a week, most people can make all they need. But because your exposure to sunlight can vary widely depending on the time of year, your location, and other factors, experts recommend that you fulfill your daily requirement through your diet or through supplements if necessary. The government mandates that milk, along with some breads and cereals, be fortified with D, although studies have found that most milk contains less than the label says. (You can also find D naturally in fatty fish such as salmon.)

You might if you don't get much sun, and you're not a big milk and cereal fan. People who live north of California or Connecticut may not get enough direct sun in the winter to meet their D needs. This is particularly a problem for older people, whose bodies don't synthesize the vitamin as efficiently and who may not be able to stomach dairy products. Most multivitamins contain 400 IU of D, though check the label to be sure. People over 70 can pick up another 200 IU by adding a calcium-plus-D supplement. They're easier to find than D alone, and you probably need the extra calcium anyway.

Teens may be at risk too, according to some doctors. Teens are spending more hours in front of the computer or TV and less time outdoors, and often opt for soda over milk. As a result, they don't get the vitamin D they need for healthy bones at a time when their bodies are growing rapidly and need it most. According to an Associated Press report, Dr. Michael Holick, a Boston University vitamin D specialist, thinks that up to 30 percent of US teens may be deficient in vitamin D. To be safe, the American Academy of Pediatrics recommends multivitamin supplements containing 200 IU of vitamin D for teens who don't drink at least 16 ounces of vitamin D-fortified milk a day.

Vitamin D toxicity can cause vague symptoms like nausea, vomiting, weakness, and weight loss. It can lead to confusion, irregular heartbeats, and kidney stones.

-- Kate Lee is a former associate editor at Consumer Health Interactive and researcher at Time Inc. Health. She is currently a senior editor at BabyCenter.

Further Resources

Roberta Larson Duyuff, MS, RD, CFCS, The American Dietetic Association's Complete Food &Nutrition Guide. Chronimed Publishing, 1996, 1998.

References

First published January 2, 1999
Last updated April 28, 2008
Copyright © 1999 Consumer Health Interactive and OneBody, Inc.

Or Find More On:

Back to top of page