With the quiet explosion in popularity of recreational bicycling in the United States, it’s natural that men would wonder about the potential health effects of spending serious time on a bike. Men, research shows, account for almost all the growth in the pastime in the last three decades. A recent study both silences some of the most prevalent fears, which center on sexual dysfunction and infertility, and raises the specter of another. It suggests that prolonged cycling may be linked to higher risks of prostate cancer in men over age 50.