The great sperm mystery: How doctors hope to solve unexplained male infertility

How do you get sperm from a crocodile? “Very carefully is the short answer,” says Brett Nixon, a professor at the University of Newcastle, who has studied the sperm of animals including platypus, rabbits and the saltwater predators to better understand human reproduction. (The long answer is that you sedate the croc and extract sperm using a method euphemistically dubbed a “digital massage”.)

A new study has found reduced sperm production and testosterone in mice exposed to forever chemicals.Credit: University of Newcastle

It turns out, compared with animals, humans are not good at making sperm. Rams ejaculate about 100 billion sperm compared with a man’s measly 100 million. The humble fruit fly unleashes monster sperm that’s six centimetres long – about 20 times its body length. Almost every sperm produced by a mouse is viable compared with only 4 per cent of human swimmers made in the right shape, Nixon says.

He’s one of many experts concerned that human sperm counts are plunging further still, and many suspect the drop is at least partly driven by a cocktail of air pollution, microplastics and other hormone-disrupting toxins including PFAS “forever chemicals” in the environment. Amid those anxieties, it remains the case that for most male infertility cases, doctors are unable to establish a cause.

Nixon’s latest work hit the headlines this week after his team showed PFAS – at levels matching contaminated groundwater at Williamtown near Newcastle – reduced sperm production and testosterone in mice, and appeared to warp sperms’ epigenome in a way that could impact embryo growth. The results cannot be directly translated to human health because, alongside other fundamental anatomical differences, the way people and mice metabolise PFAS varies. But the findings do reflect observational studies that have found a correlation between some forever chemicals and worse sperm counts in people. However, evidence on this is mixed.

“We want to look at humans and see whether the same sort of changes are occurring,” Nixon says, although he notes it’s almost impossible to draw a direct cause-and-effect relationship in humans because you wouldn’t be able to ethically expose participants to PFAS in a randomised controlled trial.

Nixon is a believer in what’s sometimes called the Sperm Count Decline hypothesis; the idea, supported by two influential meta-analyses led by Israeli epidemiologist Dr Hagai Levine, that sperm count and quality have crashed by more than 50 per cent in the last five decades.

Male fertility expert Professor Brett Nixon.Credit: University of Newcastle

“I firmly believe in that data,” Nixon says. “And the rate at which [sperm count declines are] occurring suggests this is not a genetic effect; it’s an environmental effect.”

Levine’s co-author Dr Shanna Swan has energetically popularised their findings through the book Countdown and her claims that by 2045, men’s sperm will be so lacklustre that almost all couples will have to rely on IVF. Swan has pinned the blame on endocrine-disrupting chemicals including phthalates and BPAs, which are associated with plastics.

Associate Professor Tim Moss, a biomedical researcher and expert at men’s health organisation Healthy Male, is unmoved by claims of an impending Spermageddon. According to him, studies reporting an almighty sperm crash since the 1970s are a case of “shit in, shit out”.

“We know that if you take a semen sample and send it to two laboratories, we get different answers,” Moss says. “It’s really imprecise. That’s the shit going in that produces unreliable results.”

Other fertility experts have branded the data from the 70s as being of bad quality because less sophisticated semen analysis in past decades may have overestimated sperm counts, and much of that past data is missing key information including the donors’ age. Sperm counts themselves fluctuate on short timescales depending on factors such as arousal; a 2015 study showed men ejaculate higher volumes of more spritely sperm when shown new porn videos compared with those they have already watched.

But there is one thing experts on both sides of the Great Sperm Debate agree on: for a cell so crucial to human existence, we know precious little about it. Scientists have galvanised around the rather extraordinary statistic that, in couples undergoing IVF at least partly due to male fertility problems, 77 per cent of those male infertility cases cannot be explained.

The state of data is so bad that even the male fertility rate is something experts guess at, Moss says: “Everybody seems to say that in up to 50 per cent of infertile couples, there is a male factor that contributes to it. But those data are based on a study of three regions in France conducted in the early 80s. We just don’t have good quality data about the prevalence of infertility in males.

“The infertility data that we use in Australia comes from the Women’s Health Survey, where they ask women about their experiences trying to get pregnant. We haven’t asked the men.”

US professor Dr Shanna Swan declared humanity was facing a “global existential crisis” following her research into sperm counts.

New male fertility guidelines, launched this month, urge doctors to assess both men and women from the get-go when couples seek fertility treatment. The guidelines aim to shift the onus of fertility treatment from women and to improve outcomes for men; it’s mandatory under the guidelines that men drop their dacks for physical examinations, which can lead to the quick diagnosis of easily fixed problems such as varicocele (varicose veins in the testicle, which reduce sperm production). But experts also hope greater emphasis on men’s reproductive health will help shed light on what’s behind unexplained male infertility and chip away at the paucity of data.

Professor Rob McLachlan, medical director at Healthy Male and co-creator of the guidelines, takes a “guilty until proven innocent” approach to the role of PFAS and plastic chemicals, but believes most severe cases of male infertility are probably down to genetics. Even if average sperm rates are suffering, on the whole they remain well above levels needed to conceive, and plunging birth rates are down to societal pressures rather than sperm counts, he says.

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But the question of sperm health remains vital from a public health perspective; men with greater sperm counts and faster swimmers tend to live longer. McLachlan emphasises factors men can control to boost sperm health.

“You shouldn’t be obese,” he says. “You should be exercising. You should not be smoking – that’s very bad for sperm. I’m very worried about this anti-vaccination madness. Your son must be immunised against mumps – if you get it after puberty that can lead to complete sterility.

“Women are told to not smoke and not drink and lose weight before they have a baby. We now know that being a healthy father at the time of conception – which means getting your act together well before you make the baby – is just as important.”

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