Saturday, November 22, 2008

Vitamin D

The Vitamin D Dilemma: What’s the Safest Way to Get It?

By Nissa Simon - November 14, 2008 - AARP Bulletin Today

Here’s a solar paradox: Excessive exposure to sunlight is known to cause skin cancer. But in following the much-advised mantra to wear sunscreen when outdoors, many Americans may face a greater risk of other types of cancer—as well as conditions from diabetes to depression, heart disease to hip fractures and multiple sclerosis to muscle pain.

That’s because sunlight is the body’s main supply of protective vitamin D, an essential nutrient that may be best known for keeping bones and teeth strong. But its benefits hardly end there.

“The body uses vitamin D in virtually every tissue,” says Robert P. Heaney, M.D., an expert on calcium and vitamin D at Creighton University in Omaha, Neb. “When we talk about adequate vitamin D, we’re talking about total body health.”

Unfortunately, at least half of older men and women have low levels of vitamin D, which is present in very few foods. In August, researchers from Johns Hopkins University and Albert Einstein College of Medicine reported in Archives of Internal Medicine that after adjusting for smoking, body weight and other known risk factors in 13,000 people, they found those with the lowest blood levels of vitamin D were 26 percent more likely to die during a six-year study than those with higher amounts. That study followed previous research by Austrian scientists on more than 3,200 men and women, with an average age of 62, who were scheduled for coronary angioplasty. Seven years after that procedure, those with low D levels were more likely to die—of heart disease as well as other causes.

How does vitamin D—or more specifically, a lack of it—affect age-related conditions?

• Cancer: Without enough vitamin D, cells can multiply too quickly and promote malignant tumors. A deficiency has been linked to increased risk of cancers of the breast, colon, prostate, ovaries, esophagus and lymphatic system and may explain why studies have suggested that people living in southern climates, where sunshine is more plentiful, are less likely than their northern neighbors to die from those cancers. In fact, one study in the Journal of Clinical Oncology in June notes that men and women diagnosed with colon cancer who had the highest blood levels of vitamin D were one-third less likely to die from the disease than those with the lowest levels.

• Diabetes: Vitamin D deficiency interferes with insulin secretion and may be linked to a higher risk of both type 1 and type 2 diabetes. The most recent evidence: A study by Finnish researchers published in Epidemiology in September indicates that men with the highest D levels were 72 percent less likely to have developed type 2 diabetes two decades later than those with the lowest levels.

• Heart disease: This nutrient also helps reduce inflammation, which may explain why it helps keep hearts healthy. In a review published in Circulation of more than 1,700 offspring of the original participants in the Framingham Heart Study, now middle-age and older, researchers found that those with the lowest levels were twice as likely to have a heart attack or stroke in the next five years as those with higher vitamin D levels. More recent research, published in the Archives of Internal Medicine in June, compared vitamin D levels in more than 450 men who had heart attacks with 900 men with no history of heart disease. Again, low levels were associated with higher risk.

• Depression: In a study of 1,300 folks age 65 and older, reported in the May issue of Archives of General Psychiatry, scientists from the Netherlands reported that those who were D-deficient face a greater risk of depression. Reason: Without enough D, tiny parathyroid glands located behind the thyroid become overactive, producing excessive amounts of a specific hormone. Overactive parathyroid glands are frequently accompanied by symptoms of depression that disappear after treatment, reports the American Medical Association. Meanwhile, the so-called seasonal affective disorder that causes wintertime blues has long been thought to be caused by a lack of sunshine.

• Parkinson’s: In the latest of several studies suggesting a link with this condition, Emory University researchers report that more than half of Parkinson’s patients they evaluated were vitamin D-deficient—compared with only one in three “healthy” elderly people. In addition, Parkinson’s patients were more than twice as likely to have the very lowest blood levels of D as those without this condition. This new finding, reported in the October issue of Archives of Neurology, follows a 2007 report by another research team suggesting that vitamin D deficiency might even cause this ailment.

• Bone health: Vitamin D is essential to the absorption of calcium to maintain bone density and possibly slow bone loss. In one recent study, published in Annals of Internal Medicine in August, when researchers compared the vitamin D levels of 400 postmenopausal women who suffered hip fractures with levels of 400 others who didn’t, the risk for fracture rose steadily as vitamin D concentrations fell. In addition to helping keep bones strong, D may also boost balance and muscle strength, thus preventing falls, the primary cause of hip fractures.

It doesn’t end there. A lack of vitamin D is believed to play a role in MS, muscle pain and possibly even some forms of kidney disease. And as you age, you need higher amounts: To prevent a deficiency, the recommended daily allowance is 400 international units (IUs) for men and women between ages 50 and 70; after age 71, it jumps to 600 IUs.

So how can you ensure you’re getting enough, while still reducing your risk for skin cancer?

• Get limited sun exposure of 15 to 20 minutes on unprotected skin, at least twice a week. “That amount won’t increase your risk of developing skin cancer,” says Marianne Berwick, head of the Epidemiology and Cancer Prevention Program at the University of New Mexico in Albuquerque.

• Measure your blood. “Men and women concerned about their overall health should have their blood levels of vitamin D monitored to make sure they have enough,” says Erin Michos, M.D., a researcher in a Johns Hopkins study on longevity and vitamin D. This test, called a 25-hydroxy vitamin D test, can be performed during routine screenings for cholesterol and blood sugar, and is covered by Medicare if your doctor prescribes it. If you’re not in Medicare, ask your health plan if it covers the cost.

• Mind your meals. Even though few foods contain vitamin D, the best sources include heart-healthy fish such as salmon and mackerel, eggs, cod liver oil, and fortified milk and other dairy foods. But when choosing dairy, make it low-fat: When researchers looked at the diets of nearly 30,000 women age 45 and older, they found that low-fat dairy products high in vitamin D and calcium lowered the risk of developing high blood pressure and heart disease, but higher-fat versions did not.

• Consider supplements. Many multivitamins contain 400 IUs of vitamin D. But some experts, including Michael Holick, M.D., director of the Bone Healthcare Clinic and the Vitamin D, Skin and Bone Research Laboratory at Boston Medical Center, suggest taking an additional daily D-specific supplement of 400 IUs.

Nissa Simon, who lives in New Haven, Conn., writes about nutrition and medical issues.

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