Some researchers believe that male hormones vary with the seasons. A 2003 study found that the testosterone levels of men in one Norwegian town bottomed out in summer and reached a high in late fall. A study of Danish men found similar seasonal variations (on a slightly different schedule). If these rhythms are real, they might have to do with sun exposure, summer workouts, or winter weight-gain. But studies done in sunny San Diego and snowy Boston failed to replicate the Scandinavian findings. In a 2012 review, urologists at Baylor College of Medicine in Houston concluded that some “evidence exists to support the notion” of seasonal cycles but cautioned that more research was needed.