A row has broken out over falling sperm counts after a new study found fears of ‘spermageddon’ may have been exaggerated.
Recent research has suggested that a global reproductive crisis is on the horizon, with researchers in Israel suggesting that average sperm counts could have more than halved in the past four decades.
But the seeds of discord have been sown after an analysis of the sperm counts of potential donors in Denmark revealed no significant changes over a six-year period.
“I can’t say whether this is representative of the world, but in this population, in this location, there is no real evidence of a decline,” said co-author Prof. Allan Pacey from the University of Manchester.
Writing in the journal Human Reproductionresearchers from the University of Manchester, Queen’s University in Kingston, Canada, and the Cryos International sperm bank in Denmark analyzed data collected between early 2017 and late 2022 from samples of 6,758 potential sperm donors in Denmark.
All men were between 18 and 45 years old and the samples were analyzed using computer systems.
The results suggest that although average sperm concentration and total sperm count varied over the six-year period, there were no clear patterns.
However, the team found a decline in sperm quality between 2019 and 2022, with the average concentration of motile sperm – those that can swim – and total counts falling by 16% and 22% respectively.
A decline in quality was confirmed when the team looked only at samples from men who had been accepted as donors, including those who had made at least eight donations between 2019 and 2022.
“Some of them went up in quality, some of them went down during that time, but more went down than up,” Pacey said.
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The team suggested that the Covid pandemic may have played a role in the decline, noting that lockdowns may have led to changes in working patterns, diet and levels of physical activity – factors that can affect sperm motility.
But Pacey said it is unlikely the decline is due to the virus itself, as infection rates in Denmark were not high and Covid only temporarily affects sperm quality.
“What (the Israeli team is modeling) is average data from newspapers that was never intended to answer the question,” he said. A separate review and meta-analysis published last year by a team in Italy showed no significant trends in sperm concentration in the US and selected Western European countries.
Prof. Hagai Levine of the Hebrew University in Jerusalem pushed back against criticism of his team’s work.
“We conducted two systematic reviews and meta-analyses to study long-term global trends in sperm concentration and total sperm count. The current research is simply not relevant to this question,” he said. “It was conducted in one country, over a short period of time and among a potentially biased population.”
Richard Sharpe, an expert in male reproductive health and professor at the University of Edinburgh, who was not involved in any of the studies, said the new study covered too short a period to shed any meaningful light on sperm counts .
An earlier study by Danish researchers the fact that there was no evidence of a decline in sperm quality between 1996 and 2010 did not allay concerns.
“The interpretation of (that work) was that the damage had already been done and that the sperm count of Danish men was at an all-time low, reflected in their increasing resort to assisted reproduction,” Sharpe said, adding the new finding from a decrease in mobility. Sperm count – a key measure of male fertility – only added to the concerns.
Prof. Tina Kold Jensen of Syddansk University in Denmark, who was involved in that work, said both the meta-analyses and the new work had potential drawbacks.
“I don’t think we’ll ever get the full truth,” she said. “But we have to keep trying because it is so important.”