CHICAGO (Reuters) - Sexual activity does not cause prostate cancer, and men who ejaculate frequently may even be protecting themselves against the disease, U.S. researchers reported on Tuesday. The study, which involved more than 29,000 healthy men and covered sex of all kinds including masturbation and nocturnal emissions, confirms a smaller Australian study from last July that reached similar conclusions, the authors said. Most of the previous research into the question was on whether sexual frequency caused prostate cancer, on the theory that increased production of the male hormone testosterone could prompt prostate cell growth, the study's chief author, Michael...