Findings presented Tuesday at an Orlando, Fla., meeting of the American Association for Cancer Research show that sunshine could increase the risk of human papillomavirus infection. The researchers, analyzing cancer-screening tests from Holland, found support for the theory that sunlight suppresses women's immune defenses so they are more likely to contract HPV, some strains of which are linked with virtually all cases of cervical cancer. The disease kills about 4,000 U.S. women annually. HPV also can cause anal and genital warts.
William Hrushesky of the WJB Dorn Veterans Administration Medical Center in Columbia, S.C., analyzed the results of more than 900,000 Pap tests done in southern Holland from 1983 to 1998. Although the Pap test does not detect HPV, it reveals abnormal cells typically caused by the infection. Hrushesky found that the sunnier the year and the sunnier the month, the higher the rate of HPV. August, the sunniest month in southern Holland, showed twice as much evidence of HPV as the winter months. HPV fell off sharply in September. "Sexual intercourse did not appear to explain most of the variance," Hrushesky said.
Hrushesky theorizes that even though women are exposed to HPV at roughly the same level year-round, extra sunlight in summer weakens their defenses against it. He notes that sunlight can dampen the body's production of antibodies and the activation of protective T cells, the main branches of the natural defenses against infection. Other research has suggested a connection between sunlight and susceptibility to such infections as herpes and adenovirus, among others.