From MD Consult, August 27, 2004 by Doug Kaufman

ST. LOUIS (MD Consult) - Exposure to sunlight has long been considered both boon and bane among doctors.

Too little sun can lead to ricketts caused by a lack of vitamin D. Too much sun can lead to premature aging of the skin and skin cancer. This can be confusing to people, who may wonder what to believe.

"I think we''re doing a little bit of a disservice, maybe on both sides (of the sunlight issue), to the lay public," said Dr. Lynn Cornelius, chief of dermatology at Barnes-Jewish Hospital and Washington University School of Medicine in St. Louis.

Dr. Michael Holick, a professor of medicine, dermatology, biophysics and physiology at Boston University School of Medicine, has garnered a lot of attention lately with his book, "The UV Advantage." In it, Dr. Holick says a lack of sun exposure, which interacts with skin cells to produce vitamin D, can cause serious health issues including cancer (breast, colon, prostate, ovarian), diabetes, high blood pressure, depression and multiple sclerosis.

William Grant, Ph.D., founder of the Sunlight, Nutrition and Health Research Center (SUNARC) in San Francisco, says on the SUNARC web site: "Evidence continues to mount at an accelerating rate that vitamin D is a very important risk reduction factor for a variety of diseases, not only those associated with bone health, but also those associated with internal organs, brain development while still in the womb or in infancy, and the autoimmune diseases, and even for defense against tuberculosis."

The SUNARC site also says a lack of vitamin D caused by too little exposure to sunlight can be a contributing factor to the development of several forms of cancer, including breast, colon and ovarian.

Drs. Holick and Grant aren''t recommending unlimited exposure to the sun and acknowledge the dangers of too much sun. Still, some dermatologists are skeptical about some of their conclusions, such as Dr. Holick''s belief that the higher cancer rate in the northern U.S. can be explained by a lack of vitamin D-producing sunlight.

"I don''t think Americans are vitamin D deficient," said Dr. Steven Feldman, professor of dermatology, pathology and public health sciences at Wake Forest University Baptist Medical Center in Winston-Salem, N.C.

Plus, he said, people only need about 15 minutes of sunlight a day to get all the vitamin D they need, and more isn''t better.

"After your body gets a certain amount of vitamin D in the skin, any additional sun breaks down the vitamin D that was just formed," Dr. Feldman said. "So you reach a steady state pretty quickly."

Dr. Feldman hasn''t seen any cases of ricketts in his practice and said people can get all the sunlight they need for vitamin D production just walking from their cars to buildings during the day. Further, he added, the suggestion that vitamin D accounts for the difference in cancer rates between people living in the north with less sunlight and people living in the south is "untested hypothesis."

Dr. Cornelius has read Dr. Holick''s book and said his claims need to be clearer. While many of Dr. Holick''s assumptions are based upon "some valid scientific observation," some of the conclusions reached can be misleading.

"(Studies) have found that patients with breast cancer, prostate cancer and colon cancer - not all, but certain sub-groups of patients - have a low level of vitamin D," Dr. Cornelius said. "What''s happened, in my looking at the literature and looking at what he''s saying, is that ... he and his colleagues have possibly made some assumptions that then translate to the lay public as, ''Well, if I just get more vitamin D through sun exposure, then I won''t get these cancers.''"

But it''s not that simple.

"The data we''re not telling the public, if you look critically at the literature, is it''s not so clear-cut in these patients that supplementing vitamin D will fix their vitamin D ''deficiency,''" she said. "What they have found is some of these patients have a defect in their metabolism to use vitamin D. Their vitamin D receptors, which vitamin D has to bind to to have activity, they''re finding all these ... polymorphisms, or all these mutations in the receptors for vitamin D, that more than likely translate into the ability to use vitamin D in these patients. So, in some of these patients, even if they did get vitamin D - by increasing their consumption by supplements or simply by increasing their sun exposure - it still may not affect the active form that is circulating in the blood or their ability to use the vitamin D."

Some of the science is lost in this process of summarizing studies for the public, as is the case, Dr. Cornelius said, with "The UV Advantage."

"I have a little bit of a hard time with a publication out there where statements are made such as, ''It prevents osteoporosis, it prevents cancer, it prevents heart disease, it prevents multiple sclerosis, it prevents all these other things,''" Dr. Cornelius said. "He even, in his book, makes a statement that ''The health benefits of UVB on heart health are similar to an exercise program.'' When we make such sweeping statements, there may be some basis for rational scientific observation, but we can''t make multiple assumptions based on those observations and feed it to the public, who don''t have the ability to critically look at the literature."

Dermatologists are concerned that high profile sunlight proponents like Dr. Holick will encourage people to abandon a sensible approach to dealing with sunlight and therefore put themselves at greater risk for skin cancer. Fair-skinned people, for instance, are "best-served by prudent and rigorous use of sunscreen," Dr. Cornelius said. Darker-skinned people who don''t burn still need to be prudent.

"You have to be smart about your risk factors, your family history and your skin type," she said.

Unfortunately, some people aren''t being smart about the sun, as Dr. Cornelius sees in the melanoma clinic she directs.

"The implication that we''ve kind of scared everybody into being totally pale and not getting any sun is clearly not what I see," she said. "Because even in those clinics, in that patient population, despite these patients being at high risk, ... in the summer, I routinely see two or three of my melanoma patients with sunburns."

People may try to protect themselves, but often don''t use sunscreens properly or reapply it often enough, she said.

"Even when people are trying to use sunscreens well, we still get some UV exposure through the sunscreen," she said.

Dr. Feldman said sunlight can be addictive.

"Ultraviolet light is a drug in a way," he said.

Like addictive drugs, sunlight is a two-edged sword.

"When it hits the skin, hundreds, if not thousands, of things happen – good and bad," he said.

The "bad" list is extensive.

"Ultraviolet light damages the DNA, directly, and indirectly, by activating oxygen radicals that can damage the DNA," Dr. Feldman said. "It inhibits the immune system, probably in a number of ways, by effects on chemicals in the skin, by depletion of some of the sentry cells of the immune system in the skin. It causes damage to the collagen fibers, either directly, or indirectly through the release of enzymes. It causes release of a whole variety of cytokines, signalling molecules for the immune system. And there are probably effects we don''t even know about."