The researchers said that while higher levels of testosterone were unlikely to cause cancer, they might make an existing tumour grow faster.
Older men - those in their 70s and 80s - with higher levels of testosterone, including those who undergo hormone replacement therapy, are at an increased risk of prostate cancer, according to new research.
Results from Australia's largest healthy ageing study, The Health in Men Study (HIMS), published online today in the peer reviewed journal, Cancer Epidemiology Biomarkers & Prevention, have confirmed this link.
Lead author from The University of Western Australia's Centre for Health and Ageing, Dr Zoë Hyde, said while higher levels of testosterone were unlikely to cause cancer, they might make an existing cancer grow faster.
However, Dr Hyde cautioned that this did not prove a cause-and-effect relationship.
"We need to conduct large-scale long-term trials of testosterone therapy to see if this risk applies to men receiving testosterone," she said.
The research is timely because the use of testosterone therapy is growing, and prostate cancer is very common in old age, Dr Hyde said.
Low testosterone in older men can cause loss of muscle mass, decreased sexual function, fatigue, mood changes, depression and impaired cognition. Hormone replacement therapy may seem the best approach to relieve the symptoms, but scientists now believe more research is needed on this treatment to determine if it does help patients.
They say the possibility that high levels of testosterone could make prostate cancer grow faster is concerning. A cancer that would have gone undetected and never caused any problems might now affect health.
"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.
"There is 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."
This research is part of the Health In Men Study that has been following a group of men living in Perth, Western Australia, since 1996 and is the largest study of ageing men in Australia. The study involved community-dwelling men in their 70s and 80s but excluded those receiving hormonal therapy or men with prostate cancer.
Editor's Note: Original news release can be found here.