Men who take muscle-building pills and powders are more likely to develop testicular cancer, according to a study published in the British Journal of Cancer.

Researchers conducted detailed interviews with nearly 900 US men and found that those who reported taking muscle-building supplements, such as pills and powders with creatine or androstenedione, had a 65 per cent greater likelihood of contracting testicular cancer than men who did not use such supplements.

Study senior author Tongzhang Zheng said 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 a number of years.

The study’s participants used 30 different types of supplement, although none of these have been named by the researchers. While the results suggest a relationship between supplement use and cancer, they do not prove a causal link between supplements and testicular cancer.

“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 incidences have nearly doubled since 1975, with several research studies having failed to establish a clear cause for the increase. The authors of the latest paper wrote that theirs is the first analytical epidemiological study of the possible link between supplements and testicular cancer.

When conducting their interviews with the study participants, 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. They defined “use” as consuming one or more supplements at least once a week for four consecutive weeks or more.

“Considering the magnitude of the association and the observed dose-response trends, muscle-building supplements use may be an important and modifiable exposure that could have important scientific and clinical importance for preventing testicular germ cell cancer development if this association is confirmed by future studies,” the authors conclude in the paper.