Having more than 25 lifetime sexual partners also increases odds of prostate cancer, by more than 2.5 times that of men with five or fewer sexual partners, the study found.
The conclusions are part of the Flint Men's Health Study, a population-based study of black men ages 40-79 who live in Flint, Mich. The research will be presented May 9 at the American Urological Association annual meeting in San Francisco.
The Flint Men's Health Study looked at African-American men as part of an effort to determine why black men are twice as likely as white men to develop prostate cancer and twice as likely to die from the disease.
Researchers asked 703 black men without prostate cancer and 129 black men with prostate cancer about their number of sexual partners, age at first intercourse, frequency of sexual activity and history of sexually transmitted diseases.
"Our results suggest gonorrhea may play a role in the development of prostate cancer in African-American men. Although we are unable to show that gonorrhea directly causes prostate cancer, we suspect the inflammatory effect of the gonorrhea infection may trigger pre-existing cancerous cells to multiply," says lead study author Aruna Sarma, Ph.D., assistant research scientist in the Department of Urology at U-M Medical School.
In the study, 65 percent of the men with prostate cancer reported having had gonorrhea, compared to 53 percent of men without prostate cancer. Men with prostate cancer were also more likely to report being diagnosed more than once with gonorrhea, a bacterial infection transmitted through sexual intercourse.
Other researchers have proposed a possible link between sexually transmitted diseases and prostate cancer. Previous studies have found a decreased risk of prostate cancer among men who use condoms and some evidence linking prostate cancer and various STD's.
In addition, the human papillomavirus, another common sexually transmitted disease, has been shown to cause cervical cancer in women. Scientists believe the cervical cancer develops in reaction to the inflammation caused by the HPV infection, a similar theory to why gonorrhea may play a role in prostate cancer.
Further studies are needed to determine whether gonorrhea or other STD's actually cause prostate cancer, the researchers say.
In addition to Sarma, study authors were Kathleen Cooney, M.D., from the U-M departments of Internal Medicine and Urology; John Wei, M.D., and James Montie, M.D., from Urology; David Schottenfeld, M.D., from Epidemiology and Internal Medicine; Steven Jacobsen from the Mayo Clinic; and U-M research associates Julie McLaughlin and Rodney Dunn.
The Flint Men's Health Study was funded by a U-M Specialized Program of Research Excellence, or SPORE, grant in prostate cancer from the National Institutes of Health.