Do muscle building supplements cause testicular cancer?

There is no evidence that muscle building supplements (MBS) can cause testicular cancer.

A recent study has been making rounds in the media that investigates supplements (including creatine) and their potential impact on testicular cancer.

As per our previous posts on topics like “is a high protein diet as bad as smoking?” and “does fish oil cause prostate cancer?” we wanted to analyze the actual study, beyond just the headline.

The paper

The authors of this paper wanted to investigate the relationship between testicular germ cell cancer (TGCC), the most common form of tumor-forming cancer in young men, and muscle building supplements.

In this population-based case-control study, the authors recruited male residents from various hospitals (in either Massachusetts or Connecticut) during 2006-2010. These men were histologically confirmed to have some degree of TGCC, People in the control groups were recruited from the same age demographic, and were also male residents at these hospitals.

Residents were given a questionnaire asking about their usage of “muscle building supplements“ (MBS), where ‘usage’ was defined as “at least once a week for four consecutive weeks.”

The questionnaire asked:

  • If MBS were used
  • If yes, at what age were they first used (under or above 25 years of age, since the the participants were 13 to 50 years old.)
  • Number of different supplements used (one supplement, or more than one)
  • Duration of usage (less than 12 months, greater than 36 months, or between the two)

Groin injury, cryptorchidism (about 10% of TGCC cases have a history of this, so it is considered a risk factor) and being caucasian was more common in the TGCC group compared to the control. Alcohol use, tobacco use, and education level were similar between groups.

Researchers found that male residents who reported to have used MBS had an increased risk of developing TGCC (adjusted odds ratio of 1.65 with a 95% CI of 1.11-2.46).

Other findings included:

  • Residents who reported first taking MBS after the age of 25 did not appear to be at greater risk (OR of 1.00 and a 95% CI of 0.52-1.91) whereas people starting to supplement before or at the age of 25 had a higher risk (OR of 2.21 and a 95% CI of 1.34-3.63)
  • Participants who reported taking one MBS did not have an increased risk (OR 1.38 and 95% CI of 0.87-2.17) while those reporting more than one had an increased risk (OR 2.77 and a 95% CI of 1.30-5.91)
  • People who used MBS for one year and those who used MBS for between one and three years did not have an increased risk, while people who had been using for over 36 months had an increased risk (OR of 2.56 and a 95% CI of 1.39-4.74)

Interpreting the results

Studies like these do not prove a causal relationship (taking X causes Y). Instead, they reveal a potential connection, which further research must investigate in order to determine what causes this potential relationship.

As such, this study should not be used as evidence to prove anything. Instead, it acts as a stepping stone to more in depth research.

The main issue with this study is how broad the category of ‘Muscle Building Supplements’ (MBS) is. The authors state that the participant interview included an assessment of 30 different types of MBS powders or pills but disclosed:

Specifically, the article stated that “The interview included an assessment of 30 different types of MBS powders or pills. The major ingredients, including creatine, protein, and androstenedione or its booster, were abstracted according to the product ingredients.”

The researchers also specified that the ingredients were abstracted, or taken at the word of the label. If the label claimed there was androstenedione in the supplement, the authors assumed it was true. There was no mention of analyzing the supplements to confirm this. Confounding ingredients or ‘hidden’ ingredients (those not disclosed on the label) do not seem to be accounted for. This is particularly relevant in the context of the recent revelations of poor supplement quality in the industry.

This kind of ambiguity makes it difficult to connect the results of this study with anything more specific than the general category of muscle building supplements. Moreover, it’s nearly impossible to dissect what this category actually refers to. The only three components disclosed are also very different in terms of their actions in the body.

The breakdown also seems a bit odd, since the major selling point of this article’s abstract is that people who have reported usage of something in this vague all-encompassing category even once, are at higher risk than people who have reported never using something in this category. Consuming a protein powder once a week for a four-week span at any point in your life would count as your ‘one’ usage according to the interviews used in this study.

Since the MBS category is too vague and broad to dissect, no specific recommendations can be made based off of the results of this study. The fact that it is a retrospective questionnaire with odd usage criteria of four times a month doesn’t help.

The takeaway

Ultimately, this study does not offer enough evidence for current MBS users to change their supplementing habits at all. However, this kind of study will spark interest in the topic of MBS and testicular cancer, spur more research and hopefully, result in a better questionnaire that can be used to predict relative risk of various cancers.

This study does not provide practical evidence to answer the question, on a personal level, “will this supplement I’m using give me testicular cancer?” It is, however, always a good idea to look up each ingredient in your dietary supplement in’s database to see if any provide individual cause for concern. For example, you can see that the body of existing research finds creatine to be safe.

At this moment in time, there is no reason to fear "muscle building supplements" as a group.