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How long should you be in the sun to get enough vitamin D?

The sun is a hot topic with doctors this winter.

What's causing the fuss? Recent studies suggest people may need more sun exposure for their health, which conflicts with long-standing warnings to stay out of the sun or use sunscreen to prevent skin cancer.

Those advocating for more exposure to the sun say it takes a moderate amount of sunlight to produce healthy levels of vitamin D -- the "sunshine vitamin." The body produces the vitamin from ultraviolet light.

But dermatologists say people might do themselves more harm than good if they're not careful.

"I'm absolutely mortified that this has come up," said Dr. Jane Kardashian, a Fresno dermatologist who treats people for skin cancer.

Kardashian said increasing time in the sun puts people at greater risk of sun cancer. Most people in the San Joaquin Valley get enough sunshine to produce vitamin D, she said, and deficiencies most likely are the result of dietary problems rather than from a lack of sun exposure. Vitamin D can be obtained through fortified milk, cheese, yogurt and fatty fish, among other foods, and by taking supplements.

But the sun is the major source of vitamin D. And two studies made public this month add to a growing body of work that says people may not be getting enough of the vitamin to reap its health rewards.

Vitamin D has long been associated with helping to build strong bones.

But now researchers say it may prevent deaths from internal cancers, such as those of the colon, breast, lung and prostate. They also speculate it could help prevent heart disease and stroke.

A study published last week in the online "Proceedings of the National Academy of Science" concludes that sun exposure may help cut cancer deaths.

The study, by Norwegian scientists and the U.S. Department of Energy's Brookhaven National Laboratory, found survival rates for internal cancers were better for people living in sunnier climes.

In the Jan. 9 issue of "Circulation," the journal of the American Heart Association, researchers who looked at 1,739 people from the Framingham Heart Study said vitamin D deficiency is associated with cardiovascular disease. They call for more study to determine whether eliminating vitamin D deficiency could prevent the disease.

"It's very clear that sunshine is a protective agent," said Richard B. Setlow, a senior biophysicist emeritus at Brookhaven who helped in the writing of the vitamin D and cancer study.

But Setlow said it's also known that too much sun increases the risk for skin cancer.

"If you have a lot of sunburn and a lot of vitamin D, you have a good thing and a bad thing," he said.

Dr. Soe Naing, an endocrinologist and assistant professor at the UC San Francisco-Fresno Medical Education Program, said it's too soon to recommend that people increase the amount of vitamin D to prevent cancer or heart disease.

But endocrinologists do see people with vitamin D deficiencies.

More than 50% of the elderly population in the United States and Europe have some kind of vitamin D deficiency or insufficiency, Naing said.

The elderly may need supplements to get enough vitamin D, he said. They can have problems getting outside to be in the sun. And adequate levels of vitamin D can be difficult to obtain through diet if people don't eat enough foods high in the vitamin.

An 8-ounce class of fortified milk provides about 100 international units of vitamin D. Naing recommends 600 to 800 units a day for people 70 and older.

Dr. Jil Huong Nguyen, an endocrinologist at Children's Hospital Central California in Madera, occasionally sees breastfed babies with seizures caused by low levels of calcium and vitamin D.

Babies need 200 units of vitamin D a day, Nguyen said.

If a breastfeeding mother is deficient in vitamins, the baby can be too, she said.

One of the mothers she's treated did not drink milk, didn't take calcium and vitamin D supplements, and "she hardly had sun exposure," Nguyen said.

Nguyen's colleague, Dr. Joseph Gerardi, chief of surgery at Children's, said vitamin D deficiency is rare in children. Rickets -- a bone disease caused by a lack of calcium, vitamin D and phosphorus -- affects very few each year, he said.

Sun damage is a much more common health problem, Gerardi said. His wife, Sharon Gerardi, is a dermatologist.

Marketa Limova, a Fresno dermatologist, said one in 35 Americans will get melanoma, an often deadly form of skin cancer, in a lifetime.

"In my mind, there's no question that we need to protect ourselves from UV [ultraviolet] exposure as much as we can," she said.

And Limova said she's never seen a study linking the use of sunscreen to decreased vitamin D levels.

"People don't use enough sunscreen," she said.

Those who advocate getting more sun for health say sun worshipping is not necessary. Moderation is the key to sun exposure.

Setlow said try 15 minutes in the sun. "Then put on a sunscreen so you've gotten your vitamin D, and that short exposure really won't be damaging."

But calculating the amount of sunlight needed for vitamin D can be difficult. Older individuals and people with darker skin will need more exposure to turn the ultraviolet light into vitamin D.

Limova said a few minutes of sun exposure is sufficient.

"It's like walking to your mailbox and back a couple of times a week is enough to get the reaction going," she said.

Naing recommends a "sensible exposure to sunlight." About five to 30 minutes of sun exposure to arms and legs twice a week should be enough for most, he said. Nguyen said 15 minutes of exposure to the face and hands each day will suffice.

Kardashian said use common sense. A fair-skinned person's skin can begin to turn red within five minutes in the Valley's sun.

"I don't expect people to live their lives like a troll under a bridge," she said. "But wear sunscreen."

The reporter can be reached at banderson@fresnobee.com or (559) 441-6310.

Last Updated Friday, August 22, 2014 - 02:56 PM.