‘Spermageddon’: is the world facing a male reproductive crisis? | Men’s health

The world is unwittingly walking into a male reproductive crisis, scientists warned this week as they presented data that revealed an apparent halving of average male testosterone levels over the past 50 years.

“It is mind-blowing that testosterone has declined by 50%,” Prof Hagai Levine, who led the work, told the Guardian. “This is a lot. Wake up people. Wake up.”

The finding is the latest in a series of recent results that suggest male fertility is in crisis. Levine’s team has previously documented an apparent drastic decline in global sperm counts, in what has come to be known as the “spermageddon” paper. The issue has become a preoccupation across the political spectrum.

The US health secretary, Robert F Kennedy Jr, has called declining sperm counts an “existential crisis” and Levine’s work has been seized on in the “manosphere” as proof modern society is emasculating men. The findings have also galvanised concerns about the hazardous impact of endocrine-disrupting chemicals, air pollution and global heating on human health.

Among scientists, though, the trend is disputed. While Levine and colleagues have embraced the doomsday narrative – his American co-author, Prof Shanna Swan, has suggested that sperm counts could hit zero by 2045 – others are highly sceptical. Prof Allan Pacey, a professor of andrology at the University of Manchester, is among them.

“There’s a tendency to pick the data that supports our viewpoint,” said Pacey. “For those who think the world is going to hell in a handcart and we’re all doomed, testosterone and sperm count decline make sense.”

In a more recent analysis of sperm count trajectories, using arguably more consistent measurement techniques, Pacey’s group found no evidence of a substantial decline (sperm quality, however, did appear to be deteriorating). Other attempts to replicate the findings have produced mixed results.

“Do I think there’s an issue with male infertility? Yes,” said Pacey. “But sperm count decline isn’t one that I worry about.”

A less contentious starting point is that male reproductive health is a reflection of men’s overall health. And the latest findings on testosterone are, scientists agree, likely to be in part explained by the steep increase in rates of obesity and diabetes.

“There’s been a profound shift in overall metabolic health,” said Prof Channa Jayasena, of Imperial College London and a consultant in reproductive endocrinology.

Excess body fat accelerates the conversion of testosterone to oestrogen and also disrupts the brain’s hormone signalling. Estimates vary, but in one study every one-point increase in BMI was associated with a 2% decrease in testosterone, which might be expected to lower sperm production. Being overweight can increase scrotal temperature, which ideally needs to be several degrees below core body temperature to produce healthy sperm. Diabetes is linked to lower testosterone, sperm DNA damage and erectile dysfunction.

“Obesity could easily account for all of the decline,” Jayasena said, of the reported 50-year fall in testosterone levels, a trend he finds convincing. “There’s a question mark over whether things like pollution and environmental factors could be contributing as well.”

The uncertainty is not down to a lack of inquiry. In the past decade, there have been thousands of studies looking at the possible role of environmental contaminants on an array of male fertility metrics.

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 another, from the US, found the average erect penis length had increased by 24% over the past 29 years; both sets of authors speculated that endocrine-disrupting chemicals could be altering male development.

Some studies, including one this week linking air pollution exposure to subtle changes in sperm DNA, are regarded as high quality. But as public interest in microplastics has intensified, a “race to publish” has been under way that has seen basic contamination controls overlooked and bold claims made on the back of weak evidence.

“There are studies demonstrating the presence of microplastics in the testicles and the extrapolation is that this must be really bad,” said Prof Rod Mitchell, a paediatric endocrinologist at the University of Edinburgh. “But they could just be sitting there inert and not doing anything.”

Mitchell has carried out some of the most highly controlled experiments to date, using a system involving human foetal testes tissue incubated in the body of a mouse. Previously he had discovered negative effects of certain environmental toxins in the development of rat reproductive systems.

“We started with plasticisers, phthalates, BPA – the ones that are always in the news as being potentially harmful,” he said. “We thought they were the likely candidates, but we got no change in testosterone levels, no change in the development of the testes. The animal studies are misleading.”

Mitchell is “somewhere in the middle” on whether environmental factors are driving fertility decline.

Despite making confident claims that environmental factors are to blame, Levine also acknowledges there is a large degree of uncertainty about the precise biological mechanisms involved. But there are broader health benefits in addressing air pollution and obesity, he argues, and, given the stakes, the precautionary principle should apply.

“You don’t need 90% proof,” said Levine. “Let’s say that there is a 1% chance that something we are doing now would make reproduction extremely rare in 100 years’ time. Should we do something about it? I think yes.

“Why do we need to jump off the cliff with a parachute and see whether or not it opens? Let’s get away from the cliff.”

Levine sees the issue through a global public health lens. But for individual men, the issue is brought into focus by the time- and finance-limited window available for improving their odds of having a baby. Navigating the competing claims and uncertain evidence can be “a nightmare”, said Prof Christopher Barratt, an expert in reproductive medicine at the University of Dundee.

For the increasing proportion of couples who undergo IVF treatment, a common theme is of male infertility being treated as a secondary concern, with clinics typically run by gynaecologists. Some men describe waiting months, or years, to have treatable issues diagnosed while their female partner is given successive scans and blood tests.

“It sounds incredibly simple – and quite boring – but we need to get the basics right,” said Barratt. “The man has to have a physical examination, a history taken and a semen analysis.”

There has also been no real change in sperm analysis since the 1950s, when sperm count and motility testing became more widely available.

“It can tell you really blunt stuff,” said Pacey. “No sperm: we’ve got a problem. Motility problems: you need IVF or ICSI (intracytoplasmic sperm injection).”

When low-quality sperm is identified as an issue, it is typically centrifuged to broadly separate out the healthier, denser sperm. “It’s blunt force over ignorance,” said Pacey.

Into this void, there has been a recent expansion of social media marketing of male fertility tests and supplements and “add-ons” being offered by clinics, very few of which get the “green light” of endorsement in the traffic light system used by the UK fertility regulator, the Human Fertilisation and Embryology Authority.

Of particular concern is a narrative, widely pushed by men’s health influencers and online prescribing companies, that men should be treating “low T”, or even “T-maxxing”, with testosterone replacement therapy. Pacey and others fear that publicity around the latest findings could drive more men to use testosterone gels or injections, which can, counterintuitively, halt sperm production because it causes the body to reduce its own hormone production.

“It’s like a thermostat in a home – if you put a heater in the lounge it will switch off the boiler,” said Jayasena. “But you need very high levels of testosterone in the testes in order to make sperm.

“What we really don’t need is a self-inflicted problem of indiscriminate testosterone use,” he added. “We’re unfortunately seeing a real increase across the UK, which is mirrored in other countries, such as the US and Australia, where men are buying testosterone online or being prescribed it outside of the medical indication.”

However, there is also a sense of optimism that decades of research into male fertility is about to pay dividends in the clinic.

Among the most promising techniques on the horizon are the use of microfluidics systems, which “race” sperm through microscopic mazes, obstacles and channels to select the fittest individual cell.

There is also significant interest in sperm DNA fragmentation, which increases with age. Current tests typically provide a readout of the percentage of sperm affected by problematic DNA damage, but cannot yet reliably select the healthiest individual sperm.

Given that an average ejaculation releases between 40 million and 300 million sperm cells, Barratt said improved sperm selection is the perfect problem for AI to solve.

“You’ve got such a large number of cells, they [look] different from each other,” he said. “Sperm and AI are meant for each other.”

At the radical end of new developments, Silicon Valley investors have given hefty backing to startups targeting lab-grown eggs and sperm. One company, Paterna, recently claimed to have successfully grown functional human sperm in a lab from sperm-making stem cells, and used the cells to create healthy-looking embryos, an approach the company says could in future help men who have no sperm.

“I’m very optimistic that the options for men will look different in four or five years’ time,” said Barratt.

In the meantime, the quest to understand male fertility continues, but many are keen to avoid panic in the face of uncertainty.

“I’m not worried that we’re going to die out imminently,” said Mitchell. “Some of the predictions that male sperm counts will be down to zero within 20 to 30 years – I don’t buy that. Many populations are in decline anyway, and not just because of potential slight reductions in male fertility.

“The problem, in terms of our future, might be more down to other issues about the world we’re living in.”