There have been a number of studies over the years finding environmental links to testicular cancer (such as some pesticides, smoking, and endocrine disruptors). Now another one - muscle-building supplements with creatine and androstenedione . From Science Daily:
Men who reported taking muscle-building supplements, such as pills and powders with creatine or androstenedione, reported a significantly higher likelihood of having developed testicular cancer than men who did not use such supplements, according to a new study in theBritish Journal of Cancer. Moreover, said study senior author Tongzhang Zheng, the associated testicular germ cell cancer risk was especially high among men who started using supplements before age 25, those who used multiple supplements and those who used them for years.
"The observed relationship was strong," said Zheng, who led the study at Yale University before joining the Brown University School of Public Health as a professor of epidemiology. "If you used at earlier age, you had a higher risk. If you used them longer, you had a higher risk. If you used multiple types, you had a higher risk." Testicular cancer incidence rose to 5.9 cases per 100,000 men in 2011, from 3.7 cases in 100,000 in 1975, Zheng said. Researchers aren't sure why. The work was inspired by mounting evidence that that at least some supplement ingredients may damage the testes.
To conduct the study, Zheng's research team conducted detailed interviews of nearly 900 men from Massachusetts and Connecticut -- 356 of whom had been diagnosed with testicular germ cell cancer, and 513 who had not. In the interviews, researchers asked the men not only about their supplement use but also about a wide variety of other possible factors such as smoking, drinking, exercise habits, family history of testicular cancer, and prior injury to their testes or groin....The researchers defined "use" as consuming one or more supplements at least once a week for four consecutive weeks or more.