Scientists report 50% decline in male testosterone over 50 years, debate continues
16 reported1 unconfirmed1 conflicting
Scientists presented data this week showing an apparent halving of average male testosterone levels over the past 50 years, according to a report by The Guardian. Prof Hagai Levine, who led the work, called the finding "mind-blowing" and urged public awareness. The study is the latest in a series of results suggesting male fertility is in crisis, following Levine's team's previous documentation of a global decline in sperm counts. The trend is disputed among scientists, with some researchers questioning the methodology and others attributing the decline to rising obesity and diabetes rates. The US health secretary, Robert F Kennedy Jr, has called declining sperm counts an "existential crisis." The article notes that this story was caught by only one source, so cross-referencing is not possible.
What’s reported
Scientists presented data showing an apparent halving of average male testosterone levels over the past 50 years.
Prof Hagai Levine led the work and described the finding as "mind-blowing."
Levine's team previously documented a global decline in sperm counts, known as the "spermageddon" paper.
The US health secretary, Robert F Kennedy Jr, has called declining sperm counts an "existential crisis."
Prof Allan Pacey of the University of Manchester is skeptical, saying there is "a tendency to pick the data that supports our viewpoint."
Pacey's group found no evidence of a substantial decline in sperm count using more consistent measurement techniques, though sperm quality appeared to be deteriorating.
Prof Channa Jayasena of Imperial College London said obesity "could easily account for all of the decline" in testosterone.
Microplastics have been found in seminal fluid, and exposure of pregnant rats to Pfas resulted in male offspring with abnormal sperm.
An Italian study suggested pollution could be leading to smaller penises, while a US study found average erect penis length increased by 24% over 29 years.
Prof Rod Mitchell of the University of Edinburgh found no change in testosterone levels or testes development from plasticisers, phthalates, or BPA in human foetal testes tissue experiments.
Levine acknowledges uncertainty about precise biological mechanisms but argues the precautionary principle should apply.
Prof Christopher Barratt of the University of Dundee said navigating competing claims and uncertain evidence can be "a nightmare" for individual men.
Testosterone replacement therapy can halt sperm production because it causes the body to reduce its own hormone production.
There is a reported increase in men buying testosterone online or being prescribed it outside medical indication in the UK, US, and Australia.
Promising techniques include microfluidics systems to select the fittest sperm and AI for improved sperm selection.
A company called Paterna claimed to have successfully grown functional human sperm in a lab from sperm-making stem cells and used them to create healthy-looking embryos.
Conflicting accounts
The article describes conflicting views among scientists. Levine and his co-author Prof Shanna Swan have embraced a doomsday narrative, with Swan suggesting sperm counts could hit zero by 2045. In contrast, Prof Allan Pacey's group found no evidence of a substantial decline in sperm count using more consistent measurement techniques, though sperm quality appeared to be deteriorating. Other attempts to replicate the findings have produced mixed results. Prof Rod Mitchell's highly controlled experiments found no change in testosterone levels or testes development from plasticisers, phthalates, or BPA, contradicting animal studies.
Open questions
The article does not specify the exact percentage of testosterone decline or the precise biological mechanisms driving the reported decline. It also does not clarify whether environmental factors like pollution are contributing beyond obesity and diabetes.
Misconceptions
The article addresses the misconception that testosterone replacement therapy is a solution for low testosterone, noting it can halt sperm production. It also addresses the misconception that microplastics found in testicles are necessarily harmful, with Prof Rod Mitchell stating they "could just be sitting there inert and not doing anything."
Key figures
Prof Hagai Levine, lead researcher
Prof Shanna Swan, American co-author
Prof Allan Pacey, professor of andrology at the University of Manchester
Prof Channa Jayasena, Imperial College London, consultant in reproductive endocrinology
Prof Rod Mitchell, paediatric endocrinologist at the University of Edinburgh
Prof Christopher Barratt, expert in reproductive medicine at the University of Dundee
Robert F Kennedy Jr, US health secretary
Sources: The Guardian
