Older men with high levels of testosterone may have an increased risk of prostate cancer, a new study from Australia says.
In the study, men ages 70 to 88 with higher testosterone levels were 9 percent more likely to develop prostate cancer over a seven-year period than men with lower levels.
Testosterone is needed for the normal growth of the prostate, and it's possible that high levels of the hormone accelerate the growth of prostate cancer, the researchers said.
However, the new study found only an association, not a cause-effect link. And previous studies on the topic have had conflicting results. A study published last month in the Journal of Sexual Medicine found that men who received testosterone as hormone replacement therapy were not at increased risk for prostate cancer.
Because the new study did not include men receiving testosterone therapy, larger studies are needed to examine the risks and benefits of the treatment, said study researcher Zoë Hyde, of the University of Western Australia's Centre for Health and Ageing.
Men currently receiving testosterone therapy should not stop treatment because of the new results, but their prostate health should be monitored closely during treatment, Hyde said.
The study was published online yesterday (July 26) in the journal Cancer Epidemiology Biomarkers & Prevention.
Testosterone and prostate cancer
The question of whether testosterone levels are related to prostate cancer is important, given the growing interest in testosterone replacement therapy, the researchers said.
Hyde and colleagues analyzed information from about 3,600 older men living in Perth, who had blood samples collected between 2001 and 2004. Levels of testosterone in the blood were analyzed, and men were followed for an average of 6.7 years.
During the study period, about 300 men developed prostate cancer. The higher the men's levels of free testosterone, the greater their risk of prostate cancer. (Most testosterone is not "free," but is bound to a protein. The "free" portion is thought to have the greatest influence on the body.)
The link held even after the researchers took into account factors that could affect prostate cancer risk, such as age, smoking habits, alcohol use and previous diagnosis of cancer.
No link was found between total testosterone (free and bound) and prostate cancer risk.
Experts were critical of the findings.
The results show only a weak connection between testosterone levels and prostate cancer risk, and the link might be explained by factors not assessed by the study, said Abraham Morgentaler, founder of Men's Health Boston, a medical organization that offers care to men, including treatment for low testosterone.
The study did not include information about the men's frequency of prostate cancer screening, Morgentaler said. Doctors tend not to screen or perform biopsies on men who are predicted to have less than 10 years to live, and therefore they do not pick up prostate cancer in these men. In contrast, doctors tend to screen healthier men with higher testosterone levels, Morgentaler said. (Sicker men tend to have lower testosterone levels.)
"The real interpretation of this study is only healthier men get prostate biopsies," said Morgentaler, who is also an associate professor of urology at Harvard Medical School.
Morgentaler also said prostate cancer rarely strikes when men's natural testosterone levels are the highest — in their late teens and early 20s.
No large studies that follow men forward in time have examined the effect of testosterone therapy on prostate cancer risk, Morgentaler said. However, a small study conducted by Morgentaler and colleagues last year and published in the Journal of Urology suggested that testosterone therapy given to men with untreated prostate cancer does not cause progression of the cancer.
However, the Endocrine Society, an international research organization, recommends against testosterone therapy for men with prostate cancer.
Pass it on: High testosterone is linked with a slight increase in the risk of prostate cancer in men in Australia, but more research is needed to confirm the results.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.