Sunscreen doesn't stand in way of healthy vitamin D levels

Las Vegas - Warnings to patients to wear sunscreen have come to carry nearly the gravity of the Hippocratic oath itself for dermatologists, but do those warnings, in fact, violate the oath and cause harm to patients?

At issue is the role of vitamin D, dubbed "the sunshine vitamin" because it is synthesized through the skin. Sunlight therefore represents a legitimate source for producing the vitamin. Vitamin D is best known for its important role in calcium regeneration and bone health, and in addition to sunlight, sources can include oily fish, fortified milk or vitamin supplements.

"The claim is that we're hurting people with sunscreen," says Dr. Spencer, a clinical professor of dermatology at Mount Sinai School of Medicine and a private practitioner in St. Petersburg, Fla.

The debate has been fueled in recent years by reports suggesting vitamin D could help with the prevention of melanoma, colon, breast and prostate cancers, as well as Type 2 diabetes and hypertension.

"The thought is that vitamin D prevents cancer, including melanoma, therefore lowering the vitamin D level would lower protection," Dr. Spencer tells Dermatology Times.

The issue gained further attention with the publication of Michael F. Holick, M.D., Ph.D.'s book "The UV Advantage," which makes the claim that excessive sun protection is harming public health and causing a national epidemic of hypovitaminosis D.

Dr. Holick based his argument on studies including one in which he looked at 165 healthy adults at Boston University and found that 30 percent were vitamin D deficient by the end of winter, with the conclusion being that diet, alone, is an inadequate source of the vitamin. (Am J Med 2002;112:659-662)

What is normal?

But the findings are based on a skewed definition of "normal" levels of vitamin D, Dr. Spencer argues. The levels Dr. Holick suggests as normal - about 20 ng per ml, are in fact about 30 percent higher than what is considered "normal" in the literature - generally said to be greater than 15 ng per ml, Dr. Spencer says, therefore, the subjects appeared to have below normal levels of the vitamin.

"If we apply the standard definition of normal levels, the reported problem disappears," Dr. Spencer says. "It's only when 'normal' is redefined under the 30 percent higher level used in this paper that there appears to be a problem."

Studies that counter the findings include research indicating that a group of Australians were able to maintain healthy vitamin D levels over a seven-month period, despite using broad-spectrum sunscreen (Arch Dermatol. 1995 Apr;131(4):415-421) and another in which patients with xeroderma pigmentosum, who practice rigorous sun-avoidance, still maintained normal vitamin D levels. (J Am Acad Dermatol. 1997 Dec; 37(6):942-7)

Dr. Spencer adds that, even in the absence of a dietary source of vitamin D, the amount of sunlight needed to achieve normal levels is generally only about seven to 10 minutes of direct sunlight on the face or forearms, once or twice a week.

"Who, among your patients, doesn't get 10 minutes of sunlight on their face once a week?" he questions.

One exception to that, however, may be dark-skinned blacks, who would likely need more sunlight to reach adequate vitamin D levels.