A row has broken out over falling sperm counts after a new study suggested fears of a “spermageddon” may have been exaggerated.
Recent research has suggested a global reproductive crisis could be in the offing, with researchers in Israel suggesting average sperm counts may have more than halved in the past 40 years.
But seeds of discord have been sown after an analysis of sperm counts from would-be donors in Denmark revealed no significant changes over a six-year period.
“I can’t comment on whether this is representative of the world, but in this population, at this location, there isn’t really evidence of a decline,” said co-author Prof Allan Pacey, of the University of Manchester.
Writing in the journal Human Reproduction, researchers at the University of Manchester, Queen’s University in Kingston, Canada, and the sperm bank Cryos International in Denmark, analysed data collected between early 2017 and late 2022 from samples of 6,758 prospective sperm donors in Denmark.
All of the men were aged between 18 and 45, with the samples analysed using computer systems.
The results suggest that, while 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 able to swim – and total numbers declining by 16% and 22% respectively.
A decline in quality was confirmed when the team looked only at samples from men who were accepted as donors, including those who made at least eight donations between 2019 and 2022.
“Some of them went up in [sperm] quality, some of them went down in quality over that time, but more of them went down than up,” said Pacey.
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The team suggested the Covid pandemic might have played a role in the decline, noting lockdowns might have led to changes in working patterns, diet and levels of physical activity – factors that can affect sperm motility.
But Pacey said the decline was unlikely to be down to the virus itself as infection rates were not high in Denmark and Covid only affects sperm quality temporarily.
“What [the Israeli team is modelling] is average data taken from papers that were never designed 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 criticisms of his team’s work.
“We conducted two systematic reviews and meta analyses to study global long-term trends in sperm concentration and total sperm count. The current study is simply irrelevant for 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 shine any meaningful light on sperm counts.
An earlier study by Danish researchers showing no evidence of a decline in semen quality between 1996 and 2010 did not assuage concerns.
“The interpretation of [that work] was that the damage was already done and Danish men’s sperm counts were at an all-time low, reflected in their increasing resort to assisted reproduction,” Sharpe said, adding the new finding of a decline in motile sperm count – a key metric for male fertility – only added to concerns.
Prof Tina Kold Jensen of Syddansk University in Denmark, who was involved in that work, said both meta-analyses and the new work had potential drawbacks.
“I think we’re never going to come up with the complete truth,” she said. “But we have to keep on trying, because it’s so important.”
