Defending Against Disease -- With Vitamin D
Melinda Beck writes about the importance of Vitamin D in her Wall Street Journal Health Journal column.

Interesting, they tell us we have to load up on sunscreen or we'll get skin cancer, yet if we slather it on, we limit our Vitamin D intake and that's bad, too. Some of us never spend any time outdoors, and that's not good. A Vitamin D deficiency is not good; and I'd rather spend time outdoors than eat massive quantities of cod liver oil, tuna, salmon or egg yolks, or drink a lot of milk.

Sunlight, as a source of vitamin D, is free and abundant, at least in most of the world. Supplements are almost as cheap. Yet a growing number of experts think that many people aren't getting enough vitamin D -- particularly those who work and play indoors and slather on sunscreen. And the more experts learn about what D does, the more worrisome a deficiency seems.

It's long been known that D is crucial for strong bones. But new research suggests that it also protects against a wide variety of diseases. A study in the Archives of Internal Medicine last month found that men with low D had a higher risk for heart attacks. Other studies have linked low D with cancer of the breast, ovary, prostate, stomach, bladder, esophagus, kidney and lung. Low levels of D also have been associated with high blood pressure, stroke, diabetes, periodontal disease, rheumatoid arthritis, multiple sclerosis, macular degeneration, mental illness and chronic pain.

"It sounds crazy -- until you realize that vitamin D turns into a steroid hormone that's involved in the maintenance of over 200 human genes," says John J. Cannell, founder of the nonprofit Vitamin D Council in Atascadero, Calif.

The strongest source, by far, is ultraviolet B rays from the sun, which convert a form of cholesterol into vitamin D in the skin. A person sitting outside in a bathing suit in New York City gets more vitamin D in 20 minutes than from drinking 200 glasses of milk. But UVB rays vary greatly depending on latitude, cloud cover, time of year and time of day. Above 42 degrees north latitude (a line from the northern California border to Boston), the sun's rays don't provide sufficient D from November through February. Researchers looking at latitude and disease rates have found some intriguing patterns. Type 1 diabetes, for example, is much rarer in countries like Cuba than in either New Zealand and Sweden.

Dark-skinned and elderly people don't process vitamin D from the sun as efficiently as younger, fair-skinned people. UVB rays also don't penetrate glass or sunscreen with a factor of 8 or more.

It's difficult to get much D through diet. Few foods contain it naturally -- mainly fatty fish like salmon, mackerel and tuna, as well as liver and egg yolks. Since the 1930s, most milk in the U.S. has been fortified with D to prevent rickets, a bone-softening disease.

It's widely accepted that most people need some supplemental D -- the question is, how much? Current U.S. guidelines, issued in 1997, call for 200 international units from birth through age 50; 400 IUs from 51 through age 70 and 600 IUs from 71 on. But many experts and the American Medical Association are urging the government to revisit those numbers in light of the latest research, and the Institute of Medicine is in discussions to do so.

Some groups aren't waiting. The American Academy of Pediatrics says breast-fed infants should get 400 IUs of supplemental D daily. The National Osteoporosis Foundation urges adults over age 50 to get at least 800 to 1,000 IUs to prevent fractures. Look for D3, which is more potent than D2.

You can learn your vitamin D level with a blood test, which costs about $100. It should measure 25-hydroxyvitamin D, not 1,25-dihydroxyvitamin D. A concentration of less than 20 nanograms per milliliter is considered deficient. Many cancer-prevention benefits have been seen at levels of 30 ng/ml or more. Alan Pocinki, an internist in Washington, D.C., has been testing his patients -- mostly white-collar workers with indoor jobs -- and found about half are below 20 ng/ml.

It's not possible to overdose on vitamin D from the sun; it degrades in the skin at high levels. For supplements, the Institute of Medicine set an upper limit of 2,000 IUs per day, but some experts think that's too low. Vitamin D toxicity can involve kidney stones and heart arrhythmias, but cases are very rare.

Does all this D-iscussion leave you D-izzy? "Many people are confused by the conflicting messages," says Len Lichtenfeld, deputy chief medical officer for the American Cancer Society, which suggests getting D from supplements, not the sun. "We need to know more about what the health benefits are, and what the right level is. We're a country of different ethnicities and locations and sensitivities. We probably can't make a one-size-fits-all recommendation."