How worried should we be about falling sperm counts?

Here’s a jolly thought to start the year: humanity is on its way to extinction due to a drastic decline in sperm counts. Men’s reproductive health is in such a parlous state that it won’t be long until nobody can conceive a child unassisted.

That, anyway, is the argument that’s become a perennial: every year or so – most recently just at the end of 2022 – a new sperm-counting study emerges and reignites the fears that we’re biologically condemned to extinction. How anxious should we be?

Here’s the story so far. In 1992, a seminal study was published in the British Medical Journal that claimed to show ‘evidence for decreasing quality of semen during [the] past 50 years’. It was a meta-analysis, a review paper that gathered together all relevant studies that measured sperm count since 1938, lining up their results to discern any trends. The conclusion was that the average sperm count had fallen from 113 million per millilitre (the standard unit in this field) in the early 20th century to 66 million/ml by the 1990s.

The study was torn to pieces. There simply isn’t a fair comparison, other researchers noted, between 1940s and 1990s equipment for measuring sperm count, the latter being far more accurate. Not only that, but there was very little data available for the first 30 years of the analysis (samples from a mere 184 men were included), so the comparison across time was murky. Critics re-analysed the data and found no evidence of a decline in sperm count overall.

The debate went quiet while more data accumulated. Then, in 2017, researchers put fresh data together and published a new meta-analysis. Looking at 244 data points beginning in the 1970s, average sperm count had dropped from 99 to 47 million/ml by 2011 – approximately a 50 per cent decline.