New research shows men with very low testosterone levels are at higher risk of both fatal and non-fatal cancer later in life.
But while the research found men with low testosterone were 18 per cent more likely to die of cancer years down the track, the results did not hold for prostate cancer.
Rather, prostate cancer appeared more closely linked with low levels of two other sex hormones: sex hormone-binding globulin (SHBG) and luteinising hormone.
The findings have emerged from the Androgens In Men Study (AIMS) – an international collaboration led by Professor Bu Yeap from The University of Western Australia, which is exploring links between different sex hormones and cancer in men.
For this study, published in the journal Lancet Healthy Longevity, AIMS analysed long-term data for more than 26,000 men involved in 11 cohort studies from Australia, the United States and Europe.
Analyses of sex hormones in blood samples taken earlier in life were matched to cancer outcomes for the same men in the decades following the tests.
Hormones analysed included testosterone, dihydrotestosterone (DHT), SHBG and luteinising hormone – made by the pituitary gland to stimulate the testes to make testosterone.
"We wanted to know whether the concentration of these hormones in the blood was related to the risk of men being diagnosed with, or dying from, cancer into the future," Professor Yeap said.
"What we saw was that if a man had low testosterone levels – in the lowest one-fifth compared to the highest one-fifth of the range – their subsequent risk of dying from cancer was higher, even after allowing for age and other health-related factors."
Professor Yeap said the normal range in young, healthy men was usually between 10 and 30 nanomoles per litre (nmol/L), with levels tending to be lower in older men. Levels could also be affected by modifiable factors including body mass index and physical activity, and by medical conditions such as diabetes.
"We saw that when baseline testosterone was below 8.6 nmol/L, subsequent cancer risk started increasing," Professor Yeap said.
"This suggests low testosterone is an important biomarker, so it's possible that looking at testosterone levels could help us identify men who might do poorly if they get cancer down the track."
The study also sought to establish whether there was any link between natural testosterone levels and prostate cancer risk.
"Since reducing testosterone levels is a treatment for prostate cancer there's always been a question of whether the amount of testosterone your own body makes relates to your risk of prostate cancer but based on our findings there's no evidence they are related," Professor Yeap said.
"We did find, however, that men with low levels of SHBG and luteinising hormone were at higher risk of prostate cancer."
Professor Yeap said the findings were not a signal that men should start supplementing with testosterone to reduce their risk of cancer.
"While we've shown low levels are associated with increased risk, we haven't got any evidence yet that actually giving men testosterone will reduce that risk," he said.
"What we would say to men is if they are found for whatever reason to be low in testosterone, it's important to go to the doctor for a full checkup. It may not show any sign of testicular disease, but it might show other health issues or risk factors they need to address.
"It could be a wake-up call and encouragement for men to engage in more healthy lifestyle behaviours, and to get regular, holistic checkups to stay on top of their health."
