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Science Scare of the Week: Spermpocalypse Now

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Reason Online & Science Media Centre

Are human beings about to become extinct due to falling sperm counts?

The BBC headline blares, “Sperm count drop ‘could make humans extinct’.”

 

The story is based on a new systematic review and meta-regression analysis of recent trends in both sperm concentration and total sperm count. The study, published in Human Reproduction Update, reports “a significant decline in sperm counts…between 1973 and 2011, driven by a 50–60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand.” By “unselected,” the authors basically mean young men who are screened for military service or college who are unlikely to be aware of their fertility status. (For example, the Danish military subjects its recruits to a compulsory medical examination that apparently includes measuring their sperm count and testes sizes.)

The meta-analysis encompassed the results of 185 studies involving 42,935 men from 50 countries on six continents who provided semen samples from 1973 to 2011. The researchers claim that their analysis tried to take into account confounding factors that lower sperm counts, including obesity, smoking, alcohol use, and stress. They report that sperm counts among unselected men living in rich developed countries fell from 99 million spermatozoa per milliliter in 1973 to 47 million per milliliter in 2011. Total sperm counts fell from 337.5 million to 137.5 million—a decline of nearly 60 percent.

On the other hand, the researchers found no decline in sperm counts among men living in South America, Asia, or Africa.

This not the first time a spermpocalypse has been declared. The claim was first made in 1992 article by Scandinavian researchers, who reported there had been a decline of nearly 50 percent in 50 years. Ever ready to fan the flames of panic, the publicists at Greenpeace quickly initiated a clever campaign of advertisements declaring, “You’re not half the man your father was.”

As the researchers acknowledge, their study tells us nothing about what caused the declines it identifies. Nevertheless, they speculate that it could be result of endocrine disruption from lifestyle changes and exposures to pesticides and synthetic chemicals. Endocrine disruption is the particular focus of one of the researchers, Shanna Swan, who teaches environmental medicine and public health at the Icahn School of Medicine at Mount Sinai. This study will doubtlessly be cited in grant proposals for more funding for research on the toxicologically questionable endocrine disruption paradigm.

So the extinction of humanity due to falling sperm counts near at hand? Perhaps not. In a 2013 comprehensive review of 35 sperm quality studies published after 1992, New York-Presbyterian Hospital/Weill Cornell Medical College fertility specialist Harry Fisch and a colleague looked into the trend data on sperm counts. The researchers reported that eight studies involving a total of 18,109 men suggest a decline in semen quality; 21 studies encompassing 112,386 men show either no change or an increase in semen quality; and six studies involving 26,007 men show ambiguous or conflicting results. The upshot, Fisch says, is that “allegations for a worldwide decline in semen parameter values have not withstood scientific scrutiny.” Asked if he stood by those findings, he replies, “Absolutely.”

Fisch suggests that despite their efforts to consider confounding effects, the researchers may have failed to adequately take into account the more or less reversible effects on sperm production associated with rising obesitymarijuana use, sedentary lifestyles, and testicular temperature.

Full post

see also comments by Prof. Allan Pacey, Professor of Andrology, University of Sheffield:

“I’ve never been particularly convinced by the many studies published so far claiming that human sperm counts have declined in the recent past. This is because they have mostly all suffered from one or more fatal flaw, such as only studying a relatively small number of men, being retrospective in nature, or only including men who attend fertility clinics (and are therefore not representative of men in the general population). There is also an inherent publication bias in that studies which claim to show a decline in sperm counts are far more likely to get published than those that don’t. Finally, and most importantly in my view, is that attempts to compare different studies over time have rarely taken into account the significant changes to laboratory technique we have made across the years (the effect of which will lead to lower sperm counts in more modern times as older less reliable tests generally overestimate the true sperm count). For these reasons, and more, I have never truly been convinced that the purported decline in sperm counts is anything more than a laboratory artefact and I have written as much in my 2013 article “Are sperm counts declining? Or did we just change our spectacles?” (See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3739163/)

“However, the study today by Levine and colleagues has piqued my interest because it deals head on with many of these issues. For example, it excluded studies which recruited men by virtue of their fertility status. It also included only those studies where the sperm concentration was measured using a haemocytometer (which the World Health Organisation considers the gold standard method). This latter point is particularly critical and although it does not entirely remove the scope for error, it does reduce it considerably in my view.

“Interestingly, the paper concludes that the sperm counts may have seen the greatest decline in the post industrial countries of North America, Europe and Oceania compared to others in Asia, South America and Africa. However, while it would be easy to conclude that this represents a real global difference, perhaps driven by greater exposure of pregnant women or adult men to more man-made chemicals, I think it is too premature to make this conclusion.

“In this context, I highlight a paper in the same journal (Human Reproduction Update) in December last year by Bonde and colleagues (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5155570/) showing (again by meta-analysis) that there is currently very little epidemiologic evidence linking prenatal and postnatal exposure to endocrine disrupting chemicals with male reproductive disorders (including reduced sperm counts). Moreover my own work (see https://academic.oup.com/humrep/article-lookup/doi/10.1093/humrep/des183) has also shown that there are very few identifiable risk factors for poor semen quality that can be identified in adult males.

“Whilst an apparent 52.4% decline in sperm counts may sound a lot, but from the data provided in this paper it represents an average change from ‘normal’ (99 million sperm per ml) to ‘normal’ (47 million sperm per ml). As such, I would urge journalists and editors to treat this study with caution as the debate has not yet been resolved and there is clearly much work still to be done. However, the paper does represent a step forward in the clarity of the data which might ultimately allow us to define better studies to examine this issue. Ideally, we would have funded large prospective epidemiological studies of healthy males 25 years ago and this would by now have given us a clear answer one way or the other. Unfortunately, it seems as though we might have to wait another 25 years before we might get to know the real answer.”