Scientists report 50% decline in male testosterone over 50 years
13 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 action. 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." However, the trend is disputed among scientists, with some researchers finding no evidence of a substantial decline in sperm counts when using more consistent measurement techniques. The latest findings on testosterone are likely partly explained by rising obesity and diabetes rates, scientists agree. Excess body fat accelerates testosterone conversion to oestrogen and disrupts hormone signalling, with one study linking each one-point BMI increase to a 2% decrease in testosterone.
What’s reported
Prof Hagai Levine presented data showing average male testosterone levels have halved over 50 years.
Levine previously documented a global decline in sperm counts in what is called the "spermageddon" paper.
US health secretary Robert F Kennedy Jr called declining sperm counts an "existential crisis."
Prof Allan Pacey’s group found no evidence of substantial sperm count decline using more consistent measurement techniques, though sperm quality appeared to deteriorate.
Scientists agree the testosterone decline is likely partly explained by rising obesity and diabetes rates.
One study found every one-point increase in BMI was associated with a 2% decrease 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 lead to smaller penises, while a US study found average erect penis length increased by 24% over 29 years.
Prof Rod Mitchell’s highly controlled experiments using human foetal testes tissue found no change in testosterone levels from plasticisers, phthalates, or BPA.
Some men describe waiting months or years for treatable male infertility issues to be diagnosed while female partners receive tests.
Sperm analysis methods have not changed since the 1950s.
Social media marketing of male fertility tests, supplements, and testosterone replacement therapy is increasing, which can halt sperm production.
Promising techniques include microfluidics systems and AI for sperm selection, and lab-grown sperm from stem cells by company Paterna.
Conflicting accounts
The article reports conflicting views among scientists. Levine and co-author Shanna Swan suggest sperm counts could hit zero by 2045, while Prof Allan Pacey’s group found no evidence of substantial decline. Other replication attempts produced mixed results. Prof Rod Mitchell’s experiments found no change in testosterone from common plasticisers, contradicting claims about environmental toxins.
Open questions
The precise biological mechanisms behind the reported testosterone decline remain uncertain. It is unclear whether pollution and environmental factors contribute beyond obesity. The article does not specify the exact time period or sample size for the testosterone data.
Misconceptions
The article addresses the misconception that microplastics in testicles are necessarily harmful, noting they could be inert. It also warns that testosterone replacement therapy can halt sperm production, counter to the "low T" narrative promoted by influencers.
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
Paterna, a company claiming to have grown functional human sperm in a lab
Sources: The Guardian
