MEN whose testosterone levels remain naturally high may be more likely to develop prostate and lung cancer in old age, according to an Australian study that calls into question the growing practice of hormone supplementation to maintain energy, muscle mass and sexual potency.
The Perth research followed the medical records of men in their 70s and 80s for up to a decade, finding that among those who were diagnosed with prostate cancer, the average level of testosterone circulating freely in the bloodstream was 290 picomoles per litre of blood versus 277 for those who did not develop the disease.
The picture was more pronounced for those who developed lung cancer. Their levels of free testosterone - the small proportion that is not chemically bonded to blood proteins and is therefore biologically active - averaged 317 picomoles per litre, compared with 278 for those who remained free of the disease.
The study leader, Zoe Hyde, from the Western Australian Institute for Medical Research, said prostate cancer's progression was already known to depend on testosterone, and blocking the hormone was considered the best treatment for the disease. However, the hormone's role in triggering the cancer's initial development had not been firmly established.
Lung development differed between males and females, Dr Hyde wrote in the journal Cancer Epidemiology, Biomarkers and Prevention, which might explain why testosterone appeared also to trigger lung cancer. But it was also possible the result might have been skewed by the role of smoking, which itself could raise testosterone levels, or that lung tumours were promoting testosterone rather than the reverse.
Dr Hyde and her team also looked for any link between testosterone and bowel cancer but found none. She said studies of testosterone-boosting drugs - sometimes given to men who report low energy or flagging libido - had so far been too small to determine any role in the development of cancer, and larger studies were now needed to enable ''the detection of any carcinogenic signal''.
''While some men can benefit from testosterone therapy, we still don't fully understand all of the benefits and risks of treatment,'' Dr Hyde said. She said there was ''no need for men who are currently taking testosterone to stop, but in light of our findings, prostate health should be monitored closely during treatment''.
Pharmaceutical Benefits Scheme statistics show a nearly threefold increase in subsidised prescriptions for testosterone implants, gels, patches and tablets between 2000 and 2012, and many more are thought to be dispensed on private prescriptions.