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24 May 2023

Skinny jeans, plastics, stress: what’s behind the decline in male fertility?

Why scientists are increasingly concerned about sperm.

By Sophie McBain

Eighteen months after he and his wife started trying for a baby, James D’Souza, a secondary school teacher, underwent fertility testing. Sperm analysis revealed that his count was fine, as was his motility (his sperm moved well) but there remained a problem. His morphology was zero: none of his sperm were formed properly. D’Souza was in his mid-thirties, fit and healthy, a teetotal non-smoker. Alongside the shock, and eventually the grief, the news prompted deeper questions about his identity. “Guys who are dealing with infertility are confronting their masculinity in a way that no other man does,” he recently told me. Deemed ineligible for IVF through the NHS, over the next decade the couple paid for three rounds privately. Each failed. Well-meaning friends would ask how his wife was coping, assuming that D’Souza was fine. Similarly, most online fertility forums focused on women.

D’Souza became involved in a handful of peer-support Facebook groups that emerged for men dealing with infertility, but nowadays says he’s put off by their “toxic positivity”. “The women are more emotionally aware and open. The guys who are trying to conceive are all, ‘You’ve got to try this, never give up, keep going.’ No one wants to hear from people like me, who have tried fertility treatment and there’s no happy ending,” he said to me, speaking on Zoom from his office, his voice a rapid-fire staccato, his energy apparently undimmed by a day of lessons. “‘Never give up’ is a dangerous phrase. ‘Never give up’ is: ‘I’m going to smash my head against a brick wall.’ No, you need to deal with reality: IVF fails more times than it succeeds.”

[See also: Secrets of the womb]

As well as being overlooked by society, male infertility is often under-investigated by fertility clinics more geared towards women, and yet for decades researchers have been warning that it is a growing problem. In 1992, the British Medical Journal published a first meta-analysis suggesting that sperm counts had dropped by more than 40 per cent in half a century. The most recent, largest and most global analysis of existing studies to date, published in Human Reproduction (HR) in 2022, found that the average sperm count has fallen by 62 per cent since the early Seventies and average sperm concentration (the number of sperm per millilitre of semen) has more than halved to 49 million per millilitre.

The year-on-year decline in sperm quality seems to have accelerated since 2000. Scientists believe that once sperm concentration falls below 40 million per ml male fertility is impacted. One of the HR study’s authors, the New York-based reproductive epidemiologist Shanna Swan, has warned that falling sperm counts are “threatening human survival” – what if we are facing a scenario akin to PD James’s speculative novel Children of Men, in which sperm counts dwindle towards zero? In her 2021 book Count Down Swan describes this decline as the “canary in the coal mine”: it is “Mother Nature’s way of acting as a whistle-blower, drawing attention to the insidious damage human beings have wrought on the built and natural worlds”. She has compared the public response to her findings to the way people greeted evidence of global warming 40 years ago: despite the media coverage, the implications are either denied or ignored.

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Swan became interested in the role that environmental toxins might play in reproductive health in the 1980s, when she investigated a cluster of miscarriages in California that were eventually linked to toxic waste from a semiconductor plant that had leaked into the water supply. There are all kinds of mechanisms by which men’s sperm count can be reduced, from modern lifestyles (smoking, stress, poor diet, tight underwear) to changes during male foetal development: one study found that when a woman experiences a significant life stress during pregnancy, such as bereavement or job loss, her son is at greater risk of having low-quality sperm.

But Swan pays special attention to the role played by a class of man-made chemicals known as endocrine disrupters that are ubiquitous in modern life. They were introduced with minimal regulation and safety testing, and are now found in plastics as well as in cosmetics, our food supply – virtually everywhere. Scientists have found that even in remote Greenland, the fat tissue of some polar bears contains PCB, an endocrine-disrupting chemical banned in the UK two decades ago. These bears have reduced testosterone levels, as well as smaller penises and testes. 

Unsurprisingly, the research remains contested. “We love a drama as human beings, we love an existential threat,” Allan Pacey, a professor of andrology at the University of Sheffield, told me. “Extraordinary claims need extraordinary evidence: sperm counts declining is an extraordinary claim. But the evidence is not extraordinary. The evidence is pretty ropey.”

One problem is that counting sperm is hard – much harder than you might think. Ejaculation happens in three bursts: first come the sperm, then secretions from the prostate, and then secretions from the seminal vesicles. To ensure an accurate count these viscous secretions must be mixed very thoroughly, so that the concentration is uniform; they must then be diluted precisely and the sperm immobilised, so that scientists are not required to keep count of millions of tadpoles, wriggling in all directions under a microscope.

At every stage, there is scope for error. Even now that computers can aid sperm counts, labs are not always accurate. Pacey chairs the UK National External Quality Assurance Scheme for Andrology, which means that four times a year he sends out the same sperm sample to be analysed by different labs. These frequently come back with different counts. What he’s noticed is that when people miscount sperm, they tend to overestimate – which might suggest that the apparent decline in sperm count is the result of better counting methods.

The second problem is that the link between sperm counts and fertility is complex: a man’s sperm count varies a great deal throughout his lifetime for predictable reasons (such as abstinence) and unknown ones. Pacey says he is frequently approached at fertility events by patients holding readouts of their sperm count and wondering why it has, say, dropped by 4 million between April and July, and has to tell them such fluctuations are normal. He feels scientists have become so fixated on the hypothesis that sperm counts are in historic decline that they are missing opportunities to address more pressing questions. We still don’t know, for example, exactly how common male infertility is, or what the average sperm count is in different countries.

We also have much to learn about the apparent links between poor fertility and male general health. One large-scale study of men who were attending fertility clinics found that having poor-quality sperm more than doubled a man’s chance of dying. Poor-quality sperm is linked to heightened risk of heart disease, diabetes and other life-threatening conditions, but researchers don’t fully understand why. Pacey might be sceptical of the data, but he believes that research into male infertility is dangerously underfunded and that something serious is going on: in recent decades there has also been a rise in rates of testicular cancer, as well as an increase in congenital conditions such as cryptorchidism, in which the testicles do not descend properly.

[See also: The great attention deficit: what’s fuelling the rise in adult ADHD?]

In the autumn of 2020, when James D’Souza and his wife had started considering surrogacy, he was diagnosed with testicular cancer. It was almost a decade since they had started trying for a child. D’Souza was now in his mid-forties and had no major health complaints, apart from a dragging tiredness at the end of the summer term that he had dismissed as normal, and the swollen testicle that had prompted him to visit his GP. His consultant told him that rates of testicular cancer are higher among men with fertility problems, something he had never been told. It was another shock, but D’Souza told me that undergoing cancer treatment was in some ways easier than reaching the decision to stop trying for a child. People at least knew what to say, unlike the silence that followed every time someone casually asked if he had children and he replied that he was unable to.

One of the first people to notice an apparent link between declining sperm quality and rising rates of testicular cancer was Niels Skakkebaek, a Danish paediatrician. In the early Seventies he conducted biopsies on infertile men who subsequently developed cancer and discovered that abnormal germ cells (the cells that produce sperm) – present from birth – were a precursor to testicular germ cell cancer, the most common cancer among men aged 15 to 49.

Rates of testicular germ cell cancer have been rising for decades. Skakkebaek became convinced that something was disrupting male development in utero and causing this rise, as well as a fall in sperm counts and rise in cryptorchidism. He noted that Danish men had lower sperm counts and higher rates of testicular cancer than neighbouring Finns, and theorised that this could be because Denmark was more industrialised and polluted. (His research team was later accused of trying to avoid publishing some data, though Skakkebaek denies this: one study of Danish military recruits showed that sperm counts hadn’t declined.)

A sperm sample is analysed at BioArt Fertility Clinics, Johannesburg, 2022. Photo by Luca Sola / HAFP

Skakkebaek’s work was controversial; at the time it seemed counterintuitive that to understand problems that afflicted men after puberty you needed to look at what their mothers might have been exposed to decades earlier. Today, his theory of germ cell cancer is scientific consensus, although there is disagreement over the causes. There are huge practical and ethical challenges around studying foetal development: for good reason, we don’t expose pregnant women to potentially toxic chemicals in a lab. And if environmental chemicals are to blame, might one or two substances be the problem, or could it be a cocktail of many chemicals? Population studies would have to run for decades to be of real use.

One attempt to circumvent this problem was developed by Richard Lea, an associate professor at the University of Nottingham’s School of Veterinary Medicine and Science. He has been studying sperm samples collected from stud dogs bred as assistant animals for people with disabilities. Because they live with us, dogs are exposed to the same household and environmental chemicals that we are and experience many of the same diseases. But, unlike humans, dogs eat a predictable diet, have strictly regimented sex lives and are unable to participate in many of the activities that might be responsible for modern men’s lacklustre swimmers, such as drinking, smoking, taking drugs or wearing skinny jeans. His sperm samples date back to 1988 and – unlike many other studies – they were analysed in the same lab, by the same technician.

In 2016 Lea published his findings: while the data on sperm counts was more ambiguous, the dogs’ sperm motility had fallen by 30 per cent between 1988 and 2014. There was also an increase in the number of puppies born with cryptorchidism. Lea conducted biopsies of dog testes (donated by local vets) and dog food, and found both contained at least two types of endocrine-disrupting environmental chemicals, PCB and DEHP (a phthalate used in plastics and banned in the UK in 2015). When he added these chemicals directly to samples of dog semen, he found that sperm motility and viability was reduced.

Lea is convinced that environmental chemicals such as these are a major culprit. “It’s a big, big worry,” he said. “We’re putting ever more man-made chemicals into the environment and, not only that, a lot of man-made chemicals that went into the environment in the Eighties [when the dog study began] and further back are very long lived.” He mentioned another UK study that found sheep fed in pastures enriched with fertiliser derived from human sewage – containing environmental chemicals most humans are exposed to daily – were more likely to produce rams with fewer germ cells in their testes, impairing sperm production.

Other researchers have suggested links between environmental chemicals and female reproductive health: in Count Down Swan notes that rates of miscarriage have been rising by about one per cent a year, and cites studies suggesting links with exposure to a range of substances. Another study found that women with higher levels of a plasticiser called DINCH in their urine were able to retrieve fewer eggs through IVF. Swan notes that one reason for the scientific focus on sperm counts, rather than on female reproductive health, is that men are easier to study: the relevant organs are external, and it is much easier to analyse a sperm sample than an ovarian reserve.

[See also: Mumsnet’s founder Justine Roberts: “It is a place where women can speak the truth”]

One problem with extrapolating from animal studies is that various species respond to chemical exposure differently. Scientists have discovered, for instance, that if you expose pregnant rats to phthalates (such as DEHP), their male offspring exhibit a range of problems similar to those found in humans, such as low sperm counts and high rates of testicular germ cell cancer. But mice don’t appear to be affected in the same way. In 2010 a team led by Richard Sharpe, at the University of Edinburgh, developed an ingenious if gruesome way to try to model how chemical exposure might affect humans, by grafting human foetal testes tissue (taken from aborted foetuses) on to mice. To date, the only substance that has been shown through these experiments to affect human foetal testosterone levels is paracetamol, which might indicate a correlation with women taking it over a prolonged period during pregnancy. (Sharpe added that he did not want to cause unnecessary alarm, and pregnant women who have a fever, or are in considerable pain, are still advised to take paracetamol.)

Sharpe now believes that while the majority of researchers are focused on the impact of environmental chemicals, they could be looking in the wrong direction: “Where we should be looking is at exposures to chemicals that are designed to be biologically active, which are highly potent and which humans are taking as prescription drugs,” he told me. He said that more people than ever are taking prescription medications, but relatively little attention has been paid to their impact on reproductive health.

Over the course of his long career, Sharpe, who has recently retired, has become convinced that as much as humans in the 21st century have tried to control reproduction, the process controls us. Only two weeks after an egg is fertilised, when the human embryo is a pair of fluid-filled sacs, smaller than a grain of rice, it sets aside the germ cells that will one day produce eggs or sperm in turn. And so, even when the only mark we have made on the world is a second line on a pregnancy test or an uneasy feeling in our mother’s gut, our embryonic bodies are already gearing up to produce the next generation. “Everything else is peripheral,” Sharpe said. “Our mission in life, as far as evolution is concerned, is to pass on our genes.” Which means that, were something to disrupt this biological process, it ought to be considered seriously alarming. All the evidence suggests that this is precisely what is happening – and yet there seems little political will to do anything about it.

D’Souza has been cancer-free for two years. He and his wife have decided not to have children, and made peace with the decision. If researchers such as Swan are correct in their predictions, many more men – and couples – will find themselves in a similar position. The decline in male fertility is coinciding with falling birth rates: for decades, most countries in the Global North have been reporting births below the replacement rate of 2.1 children per woman. Without immigration, these countries’ populations will start to shrink.

The reason for this baby bust is primarily not biology but something closer to choice – more young people are choosing to have fewer or no children – although our choices are shaped by our economic circumstances and social expectations. The result is that wealthy countries are becoming older and greyer, a shift that will profoundly shape their economics, politics and society. Our expectations for adulthood are changing, and those who choose to remain child-free are discovering ways to forge different kinds of families, and to find meaning and purpose beyond parenthood. Our ideas of masculinity and femininity are slowly expanding now that they are less closely tied to fatherhood and motherhood.

None of this lessens the grief of those who yearn for children. Research by Robin Hadley, a psychologist at Manchester Metropolitan University, found that involuntarily childless men experience the same level of yearning as women, a broodiness that is not socially recognised. Having been unable to have children himself, Hadley told me he had experienced an enduring sense of “outsiderdom”. Society, he felt, still does not know how to place childless men.

For his part, D’Souza is trying to turn his experiences into a positive, by coaching other men experiencing childlessness. For a long time his primary goal was to become a father, but he’s learned that there is freedom in discovering that there are many different ways to be a good man.  

[See also: The parent trap: how Britain became a very, very expensive place to raise a child]

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This article appears in the 24 May 2023 issue of the New Statesman, The Tory Crack-Up