Muscle-building supplements containing creatine could cause testicular cancer

Muscle-building supplements may increase the risk of developing testicular cancer.

A new study has found a link between those pills and powders containing creatine or androstenedione and a higher risk of the disease - by up to 65 per cent.

Men who started taking the supplements before the age of 25, or took more than one type and used them for three years or more, were most likely to be diagnosed with cancer.

Professor Tongzhang Zheng, who led the study at Yale University before joining Brown University, said: 'The observed relationship was strong.

'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.' 

The researchers were compelled to investigate the possible link after past evidence showing some supplement ingredients damage the testes. 

Testicular cancer incidence rose to 5.9 cases per 100,000 men in 2011, from 3.7 cases in 100,000 in 1975, Professor Zheng said. 

But scientists are not sure what is behind the increase.

Professor Zheng, said: 'Testicular cancer is a very mysterious cancer,' he said. 'None of the factors we've suspected can explain the increase.'  

Professor Russ Hauser, of the Harvard school of public health and a collaborator on the study, said: 'Our study found that supplement use was related to a higher risk of developing testicular cancer.

'These results are important because there are few identified modifiable risk factors for testicular cancer.' 

Researchers conducted detailed interviews of nearly 900 men from Massachusetts and Connecticut.

Of those, 356 had been diagnosed with testicular germ cell cancer, and 513 had not.

In the interviews, the scientists asked the men not only about their supplement use, but also about a wide variety of other risk factors, including smoking, drinking, exercise habits, family history and prior injuries to their testes or groin. 

After accounting for those factors, as well as age, race and other demographics, the researchers found men who used supplements were at 65 per cent greater risk of developing testicular cancer.

They defined 'use' as consuming one or more supplements at least once a week for four consecutive weeks or more. 

The odds increased to a 177 per cent greater chance among men who used more than one kind of supplement.

Men who used the muscle-building supplements for three years or longer, the study found their risk of cancer was 2.56 times higher than those who never took the substances.

And those who started using supplements at the age of 25 or younger were also found to have elevated risk, 2.21 times higher than non-users.

'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 study's authors concluded. 

They added that further research is necessary to establish a causal link between supplements and testicular cancer. 

The study was published in the British Journal of Cancer.

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