Breast cancer patients with low levels of vitamin D were much more likely to die of the disease or have it spread than patients getting enough of the nutrient, a stuidy found, adding to evidence the " sunshine vitamin " has anti-cancer benefits.

The results are sure to renew arguments about whether a little more sunshine is a good thing. The skin makes vitamin D from ultraviolet light. too much sunlight can raise the risk of skin cancer, but small amounts, 15 minutes or so a few times a week without sunscreen, might be beneficial, many doctors believe.

While the vitamin is found in certain foods and supplements, most don't contain the best form, D- 3, and have only a modest effect on blood levels of the nutrient. That's what matters, the Canadian study found. Only 24 percent of women in the study had sufficient blood levels of D at the time they were first diagnosed with breast cancer. Those who were deficient were nearly twice as likely to have their cancer recur or spread during the next 10 years, and 73 percent more likely to die of the disease.

" These are pretty big differences," said study leader Dr. Pamela Goodwin. of Mount Sinai Hospital in Toronto. " It's the first time that vitamin D has been linked to breast cancer progression."

Once thought of as helping only to develop strong bones, vitamin D is now believed to serve many purposes in the human body. A deficiency of the vitamin has been linked to several diseases and disorders. Yet many people don't get enough of the so-called sunshine vitamin.

For years, Americans have been taught that they should reach for sunscreen to protect themselves from a burn, and the skin cancer it might trigger. New research shows that by covering up, they might be sacrificing important vitamin D, which is made by the skin when it's exposed to sunlight.

Ahead of beach season, here is some guidance about the sunshine vitamin from Dr. Elizabeth A. Streeten at the University of Maryland School of Medicine.
Question: What does vitamin D do?
Answer: Vitamin D is important for the entire body. Vitamin D deficiency is associated with reduced bone strength and risk of fracture, a twofold increased risk of some cancers such as colon, breast and prostate, an increased risk of both Type 1 and Type 2 diabetes, worse control of diabetes for those who have it, decreased immune function, and possibly also heart disease. Vitamin D increases calcium absorption from the gastrointestinal tract and helps the bone become mineralized, or hardened. It also serves as a differentiating factor for cells, meaning that it helps to keep cells in their mature form and prevents them from mutating into cancer cells.

Question: Most vitamin D comes from sun exposure. How does that work, and how much sun is needed?
Answer: Ultraviolet B light contained in sunshine converts vitamin D precursors present in the skin to vitamin D. To become active, the body converts vitamin D to 1,25-dihydroxyvitamin D, the only form that the body can use. This activation occurs via a two-step process, the first in the liver and the second in the kidneys.
The truth on how much sun exposure is required is that we do not know exactly and there is significant variation among individuals. The recommendation is to get 15 minutes of sun at the peak of the day, 11 a.m. to 3 p.m., to the face, neck and arms, three times a week. However, this amount of sun has not been proven to be enough. Also, more sun is needed to make vitamin D with increasing age and increasing amounts of skin pigment. Therefore, those at highest risk for vitamin D deficiency are black Americans.

Q. How many people are deficient? Is it a growing problem or just a constant problem since there has been so much focus on using sunscreen and not enough focus on diet?
A. Vitamin D deficiency is defined as a blood level of 25-hydroxyvitamin D of less than 30 nanograms per milliliter. Up to 65 percent of Americans are vitamin D deficient, with the highest levels in the elderly. However, studies have shown that up to half of young adults and children are also deficient. We do not know if the prevalence of vitamin D deficiency is growing or not, since the accurate blood test to detect it is fairly new, about 10 years old.
There is not enough vitamin D in foods for our needs. There is substantial vitamin D only in some fish, such as salmon, swordfish, tuna, sardines and only tiny amounts in other foods. Though some of our food is supplemented, the amounts are very low, for example, 100 units per 8 ounces of milk. For the average adult to get enough vitamin D from milk, he or she would have to drink 8 cups of milk per day. To get enough vitamin D for our needs, 1000 to 2000 units daily for adolescents and adults, until more vitamon D is added to our food supply, everyone should take a vitamin D supplement, at least September through May.

Q. If sunscreen with SPF 8 and over blocks the skin's ability to make vitamin D, should people wear lower SPF lotion and reapply frequently? Does UVA or UVB protection make a difference?
A. UVB rays are what is needed for vitamin D production, whereas both UVA and UVB can cause sunburn and tan. One way to prevent sunburn and allow vitamin D synthesis is to put on sunscreen after being out in the sun for 15 minutes.

Q. Would tanning beds help, particularly in the winter when the sun isn't so strong? When should people turn to supplements or fortified foods.?
A. My opinion is that everyone, children and adults alike, needs to take a vitamin D supplement above the latitude of Atlanta, Ga., during the months of September through April. There is not enough vitamin D in foods to fulfill our requirements except for the most enthusiastic milk drinkers.
Tanning beds are, indeed, a good way to make vitamin D. However, there is no data available to support its use being safe, for example, from the risk of skin cancer, for me to recommend it to the average person. There is data in small numbers of people with gastrointestinal diseases, who sometimes can't absorb enough vitamin D from their GI tracts, that gentle use, five minutes three times a week, of a sunlamp called the Sperti vitamin D lamp improves their vitamin D production adequately to meet their needs.

Q. Anything else important to know about vitamin D?
A. I would again just emphasize that up to 10,000 units of vitamin D is safe, so toxicity is very rare and usually only seen with prescription strength vitamin D pills that contain 50,000 units of vitamin D per pill.