Experts have long suspected that sunlight has powerful -- and perhaps conflicting -- effects on the body's tendency to develop a variety of diseases. The best example is the risk of too much sun triggering skin cancer.
However, many suspect sunshine can have less obvious influences, and can even affect susceptibility to a variety of everyday viruses like papilloma. These viruses are spread through sexual contact, and they are the most common cause of cervical cancer, a disease that kills about 4,000 U.S. women annually. Although the virus can cause genital warts, most infected people have no outward symptoms.
Based on the findings of a recent study researchers say their analysis of cancer screening tests supports the theory that sunlight suppresses women's immune defenses, so they are more likely to get a virus that causes cervical cancer.However other evidence suggests that sunlight may also help protect against some other kinds of cancer.
Researchers looked at the results of more than 900,000 Pap tests done in southern Holland between 1983 and 1998. The test does not detect papilloma virus directly. But it reveals abnormal cells that are typically caused by the infection. It was found that the sunnier the year and the sunnier the month, the higher the rate of human papilloma virus.August is consistently the sunniest month in southern Holland, and the screening tests picked up twice as much evidence of papilloma virus infection then as in the winter. The virus fell off sharply in September.
Researchers say they noted that sun 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 herpes and adenovirus, among other things.
"The relationship between sunlight and cancer is complex," say researchers. However in general, these reports show that several kinds of cancer, including colon, prostate and breast, are less frequent in southern areas, suggesting that sunlight may protect against them.