Studies stoke sun squabble

April 1, 2005

National report — Two recent studies have fueled the controversy over whether vitamin D acquired through sun exposure can possibly mitigate or prevent illnesses — even potentially deadly melanoma. But whether these studies shed any new light on the topic is also the subject of sharp debate.

One study looked at 3,740 patients with malignant lymphomas (and a similar number of control subjects) and found that a history of high UV exposure appears to reduce patients' risk of developing non-Hodgkin's lymphoma (Smedby KE et al. J Natl Cancer Inst. 2005 Feb 2;97(3):199-209).

Specifically, frequent sunbathing and sunburns occurring at age 20 and five to 10 years before the survey, as well as vacations abroad, correlated with a 30 percent to 40 percent reduced risk of developing non-Hodgkin's lymphoma.

"The data is clearly becoming more compelling that sun exposure decreases one's risk of many common cancers, now including non-Hodgkin's lymphoma (Grant WB. Cancer. 2002 Mar 15;94(6):1867-1875)," says Michael F. Holick, M.D., Ph.D., professor of medicine, physiology and biophysics, and director of the General Clinical Research Center, Boston University.

But others question But others question the studies, strongly contending - as does the American Academy of Dermatology - that sun exposure poses a significant health threat.

James S. Spencer, M.D., says researchers' finding that people who reported more sun exposure actually got less non-Hodgkin's lymphoma than people with less exposure is "hard to explain, because one would think that people who get more sun get more melanoma. And people who get more melanoma get more non-Hodgkin's lymphoma (Hu S et al. Dermatol Surg. 2005 Jan;31(1):76-82)." He is clinical professor of dermatology, Mount Sinai School of Medicine, and a member of the environment committee of the American Academy of Dermatology.

Barbara A. Gilchrest, M.D., chairman, department of dermatology, Boston University School of Medicine, says that from the perspective of sun safety, the study's major weakness is that "This study is epidemiologic in nature. Presumably, the statistical analysis corrects for problems related to relatively small population size, but the inherent limitations for epidemiologic approaches remain. Epidemiologic associations are interesting, but they're certainly not cause-and-effect relationships. This limitation is often poorly appreciated by those who work in the field."

She levels similar criticisms against the second study, which links sun exposure with increased survival from melanoma (Berwick M et al. J Natl Cancer Inst. 2005 Feb 2;97(3):195-199). In this study, researchers followed 528 patients for an average of more than five years and found that sunburn, high intermittent sun exposure, skin awareness histories and solar elastosis were statistically significantly inversely associated with death from melanoma.