Episode 21: Falling sperm counts

Every so often there’s a panic in the media: sperm count is declining! The human race is on the way out! New studies regularly appear that seem to support this idea. The recent book Count Down by epidemiologist Shanna Swan argued vociferously that the culprit is plastic pollution, which apparently releases endocrine-disrupting chemicals that ruin our fertility.

Is any of that true? What do the meta-analyses, which try to gather together all the evidence on sperm counts over time, really say on this question? In this episode of The Studies Show, Tom and Stuart ask whether there’s convincing evidence of a great drop-off in fecundity - and if so, what could possibly be causing it.

The Studies Show is proud to be sponsored by Works in Progress magazine - the best place online to find brilliantly-written, idea-filled articles about science, technology, and human progress. If you’re into those topics (and let’s face it, if you’re listening to this podcast you are), take a look at their main site, as well as their Substack, to find tons of reading material for your festive season.

Show notes

* Tom’s Unherd review of the Shanna Swan book Count Down

* Link to the book

* Stuart’s Spectator article on whether there’s evidence for sperm count decline

* Detailed Astral Codex Ten article on sperm count decline and what might cause it

* Original (seminal!) 1974 article on “changing parameters of male fertility potential”

* 1992 Carlsen et al. meta-analysis, showing the following data:

* 2017 Levine et al. meta-analysis (co-authored by Swan), showing the following data:

* Response to the Levine et al. meta-analysis, worrying about some of its political implications

* 2023 follow-up meta-analysis including data from more countries

* 2022 Nature Reviews Urology article with lots of useful methodological points

* Older 2008 Fisch review/critique of the idea of a decline

* Article on regional differences in sperm quality (Edinburgh wins, kind of!)

* Debate between proponents and sceptics of the idea that sperm count is declining

* Gideon Meyerowitz-Katz’s Substack post on whether pesticides are killing your sperm…

* …responding to this meta-analysis

Credits

The Studies Show is produced by Julian Mayers at Yada Yada Productions.

This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit sciencefictionspod.substack.com/subscribe