There’s a story we’ve been told about Britain’s falling birth rate. It goes something like this: women are too focused on their careers, having children too late and risking infertility when they do finally get around to attempting to get pregnant.
It is true that women’s fertility does generally decline with age and any egg freezing clinic will happily tell you this as they take your money. But humans could face a reproductive crisis because of what’s going on with sperm and it’s as little discussed as it is serious.
Global figures have suggested that sperm counts have been in decline for some time. Men have fewer sperm and those they do have are not as good at swimming as they need to be in order to fertilise eggs.
However a new study has suggested that sperm counts have actually halved in the last 40 years and that the rate of that decline is accelerating.
The study was published in the journal Human Reproduction Update and based on 153 estimates from men who were probably unaware of their fertility. It suggests that the average sperm concentration fell from an estimated 101.2m per ml to 49.0m per ml between 1973 and 2018 – a drop of 51.6%. Total sperm counts fell by 62.3% during the same period.
Women’s fertility journeys – the agony of trying and trying, the hormonal rollercoaster that is IVF – get more coverage than ever. On the one hand, this is good. It has certainly helped to diminish stigma and open up conversations. On the other hand, the pressure of procreation combined with all the value judgments about who should have children and when, has delivered an unwelcome package containing a loud and ticking biological clock to women’s doors and forced them to sign for it.
If sperm really are in crisis, why is it not being widely discussed?
Dr Channa Jayasena is an internationally recognised expert in reproductive endocrinology and currently leads a research team at Imperial College London and works as consultant in reproductive endocrinology and head of andrology at St Mary's & Hammersmith Hospitals.
"I think there’s been a historical and deep-seated stigma [when it comes to] talking about male infertility," he explains over the phone. "I realise there has been with female infertility in the past too but in my opinion there is more when it comes to male infertility because men are much less likely to confide in others about it."
Research in 2017 by the team who produced the new data showing the startling decline in sperm focused on Europe, North America and Australia. Their new study includes data from 53 countries and has found that sperm is also declining in Central and South America as well as Africa and Asia.
Dr Jayasena says that these findings do indeed confirm a worrying trend. "A few years ago [male infertility] was listed as the number one cause for couples needing IVF treatment," he says. "So it’s right up there with having irregular ovulation or blocked [fallopian] tubes in the female partner. It’s very common indeed."
"Now there is enough research to look at what’s happening in the other continents and what they have found is very much the same thing," he explains. "Regardless of where you are geographically there appears to be a very peculiar and significant reduction in reported sperm counts."
All research is limited to some degree and this study has its own limitations because counting sperm is very difficult and not always accurate.
However Dr Jayasena says that while there have been criticisms of the study’s approach, it is the "best data we have to date and it suggests that there may be genuine reductions in sperm counts in the population".
So what’s behind the decline that researchers believe they are seeing? Nobody knows for sure but one theory is that endocrine-disrupting chemicals such as BPA (bisphenol A, a compound found in plastic) could be affecting male foetuses when they are gestating in the uterus.
This is a well-known problem in medical circles though it may not have received the widespread coverage it deserves. The UN and the World Health Organization (WHO) have already jointly warned of the impact of endocrine disruptors and stated that there should be a focus on reducing people’s exposure to them.
"This is very much an emerging story," Dr Jayasena says, "and we are just beginning to see the first convincing studies that [endocrine disruptors] are having an effect on the reproductive health of the world’s population."
"It is worrying," he adds.
Dr Jayasena also notes that lifestyle factors such as drinking, smoking, obesity and diet may also be involved in sperm decline.
"Two things have happened. One is the enormous spread of obesity, we are all metabolically less healthy than we used to be. And, secondly, the increasing use of plastics everywhere from the inside of cans to our toothpaste," he concludes.
If sperm counts are falling, can anything be done?
Dr Jayasena’s colleague Dr Lisa Webber is an expert in female fertility. She is a consultant gynaecologist and subspecialist in reproductive medicine at St Mary’s Hospital, Imperial College Healthcare NHS Trust.
She explains that it is easier to gauge and treat female fertility or infertility than it is to analyse sperm accurately.
"I don’t think that all of our men are becoming infertile," she says. "But the data are really difficult to drill into. In terms of what I would like to see in the future, I would really value a more useful test for basic semen analysis so we have something which is a bit more predictive so that we can tell young couples who have the luxury of time what the features and parameters of their sperm are."
"Whereas the conversation I am usually having is that I am spending way too much time reassuring a man that just because his sperm is outside of the normal range it doesn’t mean he is infertile," Dr Webber adds. "So we need better tests so that we can actually help people who need to be helped earlier."
However, Dr Jayasena has concerns about who might be able to access fertility treatments in future.
"We need ways of actually treating [male infertility]," he says. "The only way we have at the moment is by doing IVF treatments, which is highly effective but it's worrying that funding for IVF, as for many aspects of the NHS, is deeply under strain. And many of us worry whether IVF NHS funding will be available in 10 years’ time at all because of pressures on the economy."
Reproductive health affects everyone – even those who choose not to have children – because the size and health of our population has an impact on society, demography and how economies function. The decline of sperm seems to be an emerging problem but the good news is that fertility data, treatment and technology is improving all the time. The bad news is that funding pressures might mean it isn’t available to everyone.