Vitamin D: why we all need more

Are you getting enough vitamin D? Probably not, according to the latest research. This question-and-answer format provides a comprehensive guide to supplementing with the "sunshine vitamin"

Like Clark Kent, vitamin D accomplishes more than one might expect. And like the comic book character's heroic persona, the vitamin can save lives.

In addition to helping us use calcium for healthy bones, vitamin D protects against a host of maladies. A study published inn Photochemistry and Photobiology estimated that up to 63,000 people in the US die from cancer each year because of inadequate vitamin D.

Lack of the nutrient is quite pervasive. Research published in the Mayo Clinic Proceedings found that 36 percent of healthy young adults and 57 percent of medical inpatients were deficient in vitamin D. Another study, published in the Journal of Nutrition, found that only 4 percent of adults over age 50 obtained sufficient vitamin D from food.

Why Are We Deficient in D?

There are several factors that contribute to our shortfall:

* We shun the sun, which triggers vitamin D production in our bodies.

* Our diet contains little food that is naturally high in the vitamin

* Vitamin D-fortified foods sometimes use a form that is poorly absorbed and contain inadequate amounts.

* Vitamin D supplements may not contain the nutrient's most usable form.

Read on to find ways to increase your vitamin D intake.

Which Form Is Best?

The inactive form of vitamin D, made by our skin as a result of sun exposure or obtained from food, is like a reservoir of raw material stored in our Divers, fat tissues, muscles and blood. When needed, it's converted to an active form, actually a hormone, that tells various parts of the body what to do.

"Aside from regulating calcium absorption, vitamin D influences inflammation, the immune response and cell differentiation," says Susan Harris, DSc, a scientist and vitamin D specialist at the USDA lean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston.

For decades, scientists have known that the liver and kidneys make the active form that facilitates calcium absorption. "Now we know that it's made throughout the body in many cells in many organs," says Harris.

Problems arise when we don't have enough of the inactive, stored form.

How Much Do We Need?

For daily intake, the National Academy of Sciences suggests 200 IU up to age 50, 400 IU for ages 51-69, and 600 IU thereafter. The consensus among scientists who study vitamin D is that 1000 IU daily is a safe amount; some experts recommend even higher doses.

What Foods Contain D?

Cod liver oil is our most significant food source of vitamin D, says Bruce Hollis, PhD, pediatrics professor at the Medical University of South Carolina in Charleston and a vitamin D researcher. Other food sources include salmon, mackerel and canned sardines in oil.

Hollis points out that while fortified foods such as milk are regarded as important sources of the vitamin, they fall short. One cup of milk fortified with approximately 100 IU of vitamin D theoretically provides half the daily amount required for adults up to age 50 (200 IU).

Does Sunscreen Block Absorption?

Sunscreen is viewed as protection against skin cancer, but researchers question its possible overuse because it also blocks the ultraviolet rays that trigger our bodies to produce vitamin D. On a sunny day, we can produce up to 20,000 IU in less than an hour. For any one who is sensitive to the sun, supplements are the most viable option.

Surprisingly, regular sun exposure may decrease the risk of melanoma, the deadly form of skin cancer, although it increases risk for nondeadly forms of skin cancer, says Cedric Garland, DrPH, professor of medicine at the University of California, San Diego, and a researcher who has studied the connections between sun exposure, vitamin D and cancers. Garland recommends exposing larger areas of the skin for less time during the summer, and protecting the face with a hat. In winter months, the sun's rays are too weak to trigger vitamin D production in most of the country. According to research, this may explain the seasonality of cold and flu outbreaks--vitamin D is necessary for stimulating key immune system processes.

Can Vitamin D Help Prevent Cancer?

More than 1,000 studies support the link between a lower risk of cancer and vitamin D. A review of research in the American Journal of Public Health noted that women with the lowest vitamin D levels are five times more likely to get breast cancer than those with the highest levels--and the vitamin slows down the progression of the disease. Low levels of vitamin D correlate with up to 70 percent increase in the risk for prostate cancer and double the risk of colon cancer.

What's the Difference between D2 and D3?

Supplements and vitamin D-fortified foods may contain either D2 (ergocalciferol) or D3 (cholecalciferol) forms of the nutrient. Our bodies make D3 when we get adequate sun exposure, and this is the most usable form.