Exposure to Sunlight May Decrease Risk of Prostate Cancer, Study Finds

Prostate Cancer and Sunlight

Increased exposure to sunlight may decrease the risk of prostate cancer, according to the findings of a research team from three cancer centers, including the Northern California Cancer Center (NCCC).

Reporting in the June 15 issue of Cancer Research, the study team, led by Esther John, Ph.D., of NCCC, Sue Ingles, Ph.D., of the University of Southern California, and Gary G. Schwartz, Ph.D., of Wake Forest University, found that the prostate cancer risk for men with high sun exposure was half that of men with low sun exposure.

In men with certain gene variants, risk was reduced even further, by as much as 65 percent, the researchers said.

"We believe that sunlight helps to reduce the risk of prostate cancer because the body manufactures the active form of vitamin D from exposure to sunlight," said John, the study's lead author.

The study is the largest to date on the relationship between sunlight exposure and prostate cancer risk. Previous research by Schwartz and his colleagues has shown that the prostate uses vitamin D to promote the normal growth of prostate cells and to inhibit the invasiveness and spread of prostate cancer cells to other parts of the body.

"The genes involved are those that determine the type of vitamin D receptors a person has," Schwartz said. "These receptors, which function with vitamin D like a lock and key, vary in their ability to bind vitamin D and thus to influence cell behavior."

The researchers stressed that sunlight is not the only source of vitamin D, and that men should not try to reduce their risk of prostate cancer by sunbathing because that increases the risk of sun-induced skin cancer, especially melanoma.

"If future studies continue to show reductions in prostate cancer risk associated with sun exposure, increasing vitamin D intake from diet and supplements may be the safest solution to achieve adequate levels of vitamin D," they said in the report.

In the latest study, the researchers compared 450 non-Hispanic white patients in the San Francisco Bay Area who had advanced prostate cancer with a matched control group of 455 men who did not have prostate cancer. Advanced prostate cancer was defined as cancer that had penetrated through the prostate capsule either to the same region of the body or spread to distant sites.

The scientists measured sun exposure by comparing pigmentation of underarm skin, which usually is not exposed to sunlight, with forehead pigmentation, which is. There was no statistical difference in the underarm measurement between the prostate cancer cases and the control group. But when the difference between forehead color and underarm color was compared, the control group had significantly darker pigmentation than the cancer patients.

"Increasing darkness was associated with a trend of decreasing risk of prostate cancer," they said. The scientists also obtained a sun exposure history from each participant so they could track outdoor activity. "Reduced risk of advanced prostate cancer was associated with high sun exposure determined by reflectometry and high occupational outdoor activity."

Further studies in large populations, including non-whites, are warranted to confirm the combined effects of sun exposure and genotype and define the exposure period that is important in influencing prostate cancer risk, the researchers said.

David Van Den Berg, Ph.D., of the University of Southern California also participated in the study. The work was supported by the Cancer Research Fund of the California Department of Health Services.

______________________

The Northern California Cancer Center (NCCC) is dedicated to preventing cancer through population-based research and community education. An independent organization, NCCC is an established, nationally recognized leader in understanding who gets cancer and why, and how to improve the quality of life for individuals living with cancer. In addition to its research and education programs, NCCC operates the nine-county Greater Bay Area Cancer Registry, the statewide Cancer Information Service Partnership Program, and Cancer Detection Programs: Every Woman Counts (1-800-511-2300). - FREMONT, Calif., June 15, 2005 - http://www.nccc.org