Getting Enough Vitamin D?

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.

"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, CA.

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.

The strongest source, by far, is ultraviolet B (UVB) rays from the sun, which convert a form of cholesterol into vitamin D in the skin.

Dark-skinned and elderly people don't process vitamin D from the sun as efficiently as younger, fair-skinned people.  Ultraviolet B (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.

Since the strongest source is ultraviolet B rays from the sun, spending 20 minutes outside in the noontime sun in New York City in July will provide you with 20,000 IUs.

Source: The Wall Street Journal, July 15, 2008