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You've probably never given vitamin D much thought. Maybe you've assumed that taking a daily multivitamin is all you need to keep your vitamin D bases covered. Or maybe you figured that since many foods -- from milk to bread -- are fortified with vitamin D, you just didn't have to worry about it.
You'd be wrong. Research suggests that we're not getting nearly enough vitamin D -- even the experts are shocked. "An estimated 50 percent of Americans now have a vitamin D deficiency," says Michael F. Holick, MD, PhD, professor of molecular medicine, physiology, and biophysics at Boston University School of Medicine. That's a real concern because low levels of this nutrient can cause bone pain and may lead to depression and heart disease -- even to some cancers.
Doctors are now so worried that they're testing patients' blood for vitamin D in record numbers. One lab, Quest Diagnostics, of Madison, New Jersey, saw an astounding 85 percent jump in blood tests for the nutrient from September 2007 to September 2008, and other labs report similar increases.
Often called the "sunshine vitamin," D is a nutrient that your body produces when exposed to sunlight, and it's essential for helping your bones absorb dietary calcium. Without enough D, bones can soften -- a condition called osteomalacia, which can cause bone pain, muscle weakness, and eventually fractures. Children with low D levels can get rickets, a bone disease that often leads to bow legs and skeletal and dental deformities, among other problems.
But over the past few years there has been an explosion of research that links vitamin D deficiency to an increased risk of such illnesses as breast cancer, heart disease, multiple sclerosis, arthritis, and type 1 diabetes. Lack of D can also weaken your muscles so severely that you have trouble getting out of a chair or walking up a f light of stairs. And it also can cause blue moods, unexplained aches and pains, and fatigue during the winter, says Dr. Holick.
Before D was added to milk, beginning in the 1930s, many American children developed rickets because they didn't get enough of the vitamin. Since then, foods such as cereal, butter and margarine, yogurt and cheese have also been D fortified. As a result, rickets and D deficiency pretty much dropped off doctors' radar -- until this past October, when the American Academy of Pediatrics doubled its recommended amount of the vitamin for babies, children, and teens.
But though doctors are starting to think about D, many don't realize how many conditions a D deficiency can cause. Ellen Teplitz, 54, of Marlborough, Massachusetts, found this out the hard way when her family doctor thought her abnormally high level of parathyroid hormone was a signal that one of her parathyroid glands was malfunctioning. But vitamin D deficiency can also raise parathyroid hormone levels. It turned out Teplitz did not need surgery, as her first doctor suggested, but massive doses of vitamin D to correct a deficiency.
Similarly, women with low bone density should be tested for vitamin D before taking bone-saving drugs or extra calcium, says Susan Haden, MD, an endocrinologist at the Fish Center for Women's Health at Brigham and Women's Hospital, in Boston. "Curing a D deficiency can increase bone density by up to 11 percent," she says.
How much D should healthy people get? While the recommended dietary allowance (RDA) is still 200 International Units (IUs) a day for adults ages 19 to 50, many experts believe that's not nearly enough. Dr. Haden, for instance, advises her patients to take 800 to 1,200 IUs per day depending on their test results. Older people may need even more.
But getting enough D can be difficult. The problem is that the prime source of the nutrient is sunlight, and because women have become more conscientious about wearing sunscreen and staying out of the sun, they're getting less and less of the vitamin. (Obviously, being indoors cuts off the D supply, one reason that elderly people living in nursing homes are at high risk for D deficiency.)
If you live in a Northern state you face another challenge. The angle of the sun's rays in winter makes it impossible to get enough natural sunlight for you to reach your vitamin D quotient from October through April. The body can store extra vitamin D, but most Northerners don't stockpile enough during the summer to carry them through the winter.
Getting ample D in your diet is tough, too. One of the richest dietary sources of the nutrient is D fortified milk (regular, organic, and Lactaid milk all have D; soy milk may not) and D-fortified foods; oily fish, such as salmon, tuna, mackerel, and sardines naturally contain D. To get 1,000 IUs, however, you'd have to down 10 eight-ounce glasses of milk or eat three servings of salmon daily.
Finally, the darker your skin, the greater your risk for a deficiency. A 2002 study in the American Journal of Clinical Nutrition showed that 42 percent of African-American women were seriously D deficient. Because skin pigment keeps sunlight from being absorbed as quickly, dark-skinned people need up to six times as much daily sunlight exposure as do those with light skin.
The good news is that there are some simple strategies for keeping your vitamin D levels healthy all year long.
Head outside. Get 10 to 15 minutes of unprotected sun exposure daily during the summer before you apply sunscreen. That's not hard: Walking the dog or unloading your groceries from the car should do the trick. Try to get sunlight exposure in winter, too, though you're more likely to need to up the vitamin D you get from food or supplements if you live in a Northern state.
Pop a supplement. Take a daily multivitamin or supplement that adds up to 800 IUs of D (doctors used to recommend the D3 form of the vitamin rather than D2, but recent research found they work equally well). Added to whatever D you get from your food and the sun, these pills should help raise your D level to where it should be (don't forget to count the D in any calcium pills you take). The safe upper limit for vitamin D is 2,000 IUs, so it's hard to take more than you need.
Know your D level. You can ask your doctor to measure it, but health insurance may not cover the $30 to $50 blood test if you don't have a valid medical reason for getting it, says endocrinologist Michael Kleerekoper, MD, a spokesman for the American Association of Clinical Endocrinologists. If it turns out you have a mild deficiency, boosting your D intake with at least 1,000 IUs per day for several weeks should be enough. If your deficiency is more severe, your doctor may need to rule out other possible causes, such as celiac disease, before he or she can tackle the deficiency, says Dr. Kleerekoper. To raise Ellen Teplitz's D level, her doctor prescribed a weekly supplement containing 50,000 IUs of vitamin D. (Take such megadoses only under your doctor's supervision to avoid the risk of kidney problems.) Then Ellen switched to 50,000 IUs of D once a month, a dose she continues to take along with a multivitamin and a calcium supplement.
The safe upper limit: 2,000 IUs
The new recommendation: 800-1,200 IUs
The U.S. RDA (by age):
Age 19-50: 200 IUs
Age 51-70: 400 IUs
Age 71+ 600: IUs
Because many children don't regularly drink enough milk or get enough sunlight, the American Academy of Pediatrics doubled its recommendation for the amount of vitamin D children need from infancy through age 18. Instead of 200 IUs, kids should now get 400 a day. If you're worried about your child's vitamin D intake, talk to your pediatrician about giving him a supplement.
Originally published in Ladies' Home Journal, January 2009.