Researchers discovered a link between using muscle-building supplements and an increased risk of testicular cancer. The study was published in the British Journal of Cancer and examined data from 356 adult men who had been diagnosed with testicular cancer and 513 men who had not. The men were interviewed regarding their history of supplement use, smoking and drinking habits, exercise regimens, and family disease history. After taking into account these various factors, researchers concluded that the men who had used muscle-building supplements had a 65% increased risk for testicular cancer compared to the men who hadn’t used muscle-building supplements. The risk went up for men who took more than one kind of muscle-building supplement, took such supplements for three or more years, or started taking these supplements before the age of 25. While concerns do exist surrounding how some performance-enhancing supplements may negatively affect health—and this research suggests even more strongly that consumers should only choose science-backed products from reputable manufacturers—there are two potential limitations to this study:

• The study was observational, and so by design was not capable of demonstrating a cause-and-effect relationship between taking muscle-building supplements and the observed increase in the incidence of testicular cancer. For example, it is possible that men who took such supplements had other risk factors and were more likely to have certain habits that researchers did not account for, and which may have contributed to the increased cancer risk, rather than the supplements themselves.
• According to a statement by the Council for Responsible Nutrition, a leading supplement industry trade group, the study may not have separately identified which muscle-building supplements were associated with increased risk, but rather lumped them into a single group; these include ones like androstenedione, an illegal drug that theoretically may be more likely to be associated with harm to testicular tissue, and ones like protein, for which there is little evidence to suggest a link to cancer.
• The Washington Post reported that the study did not identify which supplement brands were used by the men. If this is the case, it would not be possible to know who the manufacturers of the supplements were. Therefore, it would be difficult, if not impossible, to determine whether the supplements were properly manufactured, and whether any possible safety issues were due to contaminants or to the supplement ingredients themselves.

Source: British Journal of Cancer