A row has erupted over falling sperm counts after a new study suggested fears of a “spermageddon” may be overblown.
Recent research has suggested that a global reproductive crisis may be in the offingwith researchers in Israel suggesting average sperm counts may have more than halved in the last 40 years.
But seeds of disagreement were sown after an analysis of sperm counts from prospective donors Denmark revealed no significant changes over a six-year period.
“I can’t comment on whether it’s representative of the world, but in this population, in this location, there’s not really evidence of a decline,” says co-author Prof Allan Pacey, of the University of Manchester.
Write in the journal Human Reproductionresearchers at the University of Manchester, Queen’s University in Kingston, Canada, and the sperm bank Cryos International in Denmark, analyzed data collected between early 2017 and late 2022 from samples from 6,758 prospective sperm donors in Denmark.
All the men were between 18 and 45 years old, with the samples analyzed using computer systems.
The results suggest that, although the 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 numbers declining by 16% and 22%, respectively.
A decline in quality was confirmed when the team only looked 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 in [sperm] quality, some of them have gone down in quality over that time, but more of them have gone down than up,” Pacey said.
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The team suggested that the Covid pandemic played a role in the decline, noting that lockdowns may have led to changes in work patterns, diet and levels of physical activity – factors that can affect sperm motility.
But Pacey said the decline was probably not due to the virus itself, as infection rates were not high in Denmark and Covid only temporarily affects sperm quality.
“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 USA and selected Western European countries.
Prof Hagai Levine, from the Hebrew University in Jerusalem, hit back at criticism 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 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 either study, said the new study covered too short a period to shed any meaningful light on sperm counts.
A previous study by Danish researchers the fact that there was no evidence of a decline in semen quality between 1996 and 2010 did not alleviate concern.
“The interpretation of [that work] was that the damage had already been done and that Danish men’s sperm counts were at an all-time low, reflected in their increasing recourse to assisted reproduction,” Sharpe said, adding the new finding of a decline in motile sperm count – a key measure of men. fertility – only added to concern.
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 whole truth,” she said. “But we have to keep trying, because it’s so important.”
