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expert reaction to study of sperm counts over time

A study published in Human Reproduction Update looks at temporal trends in sperm count.


Dr Sarah Martins da Silva, Reader in Reproductive Medicine, University of Dundee, said:

“This publication considers data on sperm counts from 233 scientific studies published since 1981. The researchers published this data previously (2017), but have updated to include 38 newer studies (14233 samples) from 2014 – 2019, importantly from all areas of the globe. Their findings confirm that sperm counts are falling by around 1.1% per year, with an overall decline of 51.6% in 45 years. Of concern, the rate of decline has doubled since 2000. And we genuinely don’t know why. Exposure to pollution, plastics, smoking, drugs and prescribed medication, as well as lifestyle, such as obesity and poor diet, have all been suggested to be contributory factors although effects are poorly understood and ill-defined.

“Infertility is a global health problem. Despite an apparently booming population (8 billion announced today), 1:6 couples are estimated to experience difficulties conceiving. Male fertility problems are increasingly common and account for almost half of all cases. This data represents the story of declining fertility rates. Critics of this study might cite that we count sperm differently to 40yrs ago, that microscopes are better and that they don’t believe the findings. But the numbers and consistent findings are difficult to ignore. All studies in this publication used the same way of counting sperm (haemocytometer). And the authors only included published data for men with known fertility or unselected for fertility. Men that were infertile, taking medication or with medical conditions that may affect their fertility, smokers etc were all excluded.

“The conclusion is that sperm counts are falling. The human race is not at immediate risk of extinction but we really need research to understand why sperm counts are falling and to prevent other unintended implications for male health.”


Prof Richard Sharpe, MRC Centre for Reproductive Health, University of Edinburgh, and Member of the Society of Endocrinology, said:

“The study (together with previous studies from the same authors) speaks for itself by reaffirming that sperm count in Western men of reproductive age has been on the decline for decades and adds new data to show that this appears to be probably a world-wide phenomenon. The big questions that such findings raise is whether this is a continuing trend and where might it end up.

“Based on the present analysis the decline appears to be continuing (and maybe worsening), but I doubt that it will ever reach rock bottom (based on what has been found in secular studies in Denmark). Nevertheless, the key point that needs to be made (once again!) is that this is desperately bad news for couple fertility, because in our modern world (across the globe) couples are delaying putting their fertility to the test until the female partner is in her 30’s-40’s, when her fertility (=chances of conceiving) is already reduced by 30-60% compared with in her 20’s and will continue to decline with her age. If her male partner has a low sperm count (and the present data shows that this is increasingly likely), then we know from prospective couple studies that the chances of him impregnating his partner are reduced – he may be able to get her pregnant but it will take longer and time is not on their side (because of the progressive decline in the female partners fertility as she ages); and the lower his sperm count the longer it will take. As I term it a perfect recipe for increased couple infertility!

“And remember that recourse to assisted reproduction is unlikely to be of much use as its effectiveness also reduces progressively with age (including of the male). Furthermore, obesity simply exacerbates the fertility issues (ie makes every aspect worse). Aging societies, such as those across Europe/UK, means that these issues are not just a problem for couples trying to have kids, they are also a HUGE problem for society in the next 50 odd years as less and less young people will be around to work and support the increasing bulge of elderly folk!

“In our COP-fuelled age, we also need to be mindful that the ‘effect’ on sperm count is environmental (lifestyle and/or exposures), even if we remain unclear about the actual cause(s).”


Prof Allan Pacey, Professor of Andrology at the University of Sheffield, said:

“Whether or not human sperm counts have and are falling is a really important question that we haven’t got to grips with in a serious way in my opinion. The authors of this paper have conducted a very elegant meta analysis and I have no criticism at all about the way they have done this.

“However, I remain concerned about the quality of the data in the papers that were published (particularly in the far past) and upon which this new (and previous) analysis was based. The fact that there are now more studies in this new analysis and from different parts of the world such as South/Central America, Asia and Africa doesn’t get around that fundamental problem in my view.

“Counting sperm, even with the gold standard technique of haemocytometry, is really difficult. I believe that over time we have simply got better at it because of the development of training and quality control programmes around the world. I still think this is much of what we are seeing in the data.

“There have been a couple of other interesting articles which have raised other concerns about this approach, so I am not alone in my skepticism.

“In the December 2021 edition of Fertility and Sterility there was a debate article showing both the for and against sides of the coin:

“Also, in the August edition of Nature Reviews Urology there was a fabulous article by Jaques Auger critiquing the whole approach to this kind of study:

“I’d suggest journalists take a look at both of these papers and maybe contact the authors for their view as well.

“I don’t think this new meta analysis takes us any further forward to be honest, although I suspect it will be widely reported as a new catastrophe. The problem is that the notion of a decline in sperm counts has got into popular culture and so it’s very difficult to have an even handed debate about the issue (even among scientists).

“I recently said in an interview for The Guardian ( that like Carl Sagan once said if you’re going to make an extraordinary claim, you need extraordinary evidence.

“I don’t see extraordinary evidence here in this new paper quite frankly and so I am going to sit firmly on the fence for a while longer.”


Dr Channa Jayasena, Reader in Reproductive Endocrinology, Imperial College London, said:

“The authors have updated a previous analysis on worldwide trends in sperm count, to include global regions outside ‘The West’. In keeping with their previous report, a global reduction in sperm counts is observed. This important study serves to highlight an important area of health concern.

“The authors have combined data from several published studies spanning 50 years. However, there are specific methods for reporting sperm count, which have changed little over than period.

“The conclusions fit with a growing narrative that the average health men is declining from reasons such as obesity, reduced exercise, pollution, and environmental chemical exposure. Evidence linking all of these conditions to male infertility is published. We need to create simple health measures that can improve sperm counts in men. This will help more couples have babies without needing fertility treatment.”



‘Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries’ by Hagai Levine et al. was published in Human Reproduction Update on 15th November




Declared interests

Dr Sarah Martins da Silva: “I’m not sure that I have any conflict of interest but I am a fertility specialist and run a translational research programme focussed around understanding sperm biology, drug discovery for male infertility and contraception.”

Prof Richard Sharpe: “I’ve no conflicts to declare.”

Prof Allan Pacey: “Editor in Chief of Human Fertility, the Chairman of the Steering Committee for the UK National External Quality Assurance Scheme for Reproductive Sciences, a trustee of the Progress Educational Trust (Charity Number 1139856), and a Temporary Advisor to the World Health Organisation Guideline Development Group for global guidelines on the prevention, diagnosis and treatment of infertility (all unpaid). In addition, Allan is: (i) Chair of the Cryos International Scientific Advisory Board; (ii) a member of the Exceed Health Scientific Advisory Board; and (iiI) a member of the Cytoswim Ltd Scientific Advisory Board. But all fees associated with these are paid to the University of Sheffield and used to support teaching and research.”

Dr Channa Jayasena: “Funded by National Institute for Healthcare Research. Investigator-led grant from Logixx Pharma Ltd.”

For all other experts, no reply to our request for DOIs was received.

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