The western-styled world is losing its sperm. There's no denying it, says a meta-regression analysis comprising studies from New Zealand to the US. But not to worry, say Germany's leading reproductive biologists.
If the methodology and extrapolations are correct in a new analysis published Tuesday, and it appears they are, then the western world's sperm count has taken a massive dive.
A team led by Hagai Levine at Jerusalem's Hebrew University suggests sperm counts fell by over 50 percent from 1973 to 2011.
However if you saw this article's headline and thought you would get a scientific explanation for the low birthrates in the United States, Australia, New Zealand and most of Europe, compared to countries in Africa, Asia and South America, we regret to have to let you down.
These figures don't explain that – not yet.
And that, even though the average sperm count in the African, Asian and South American nations included in the analysis didn't show the same decline as the countries in question.
But the science itself seems to be sound.
"This analysis is no grounds for fears of male infertility in these countries," said Stefan Schlatt, director of the Center for Reproductive Medicine and Andrology (science of men) at Münster University.
Schlatt, who had nothing to do with the analysis, told DW it was "the first of its kind, very sophisticated and statistically solid," but that both the reasons for the reduced mean sperm count - and its implications - were still up in the air.
"There is something happening in the western world to our sperm count, no doubt, but we have to think about the conditions that lead to the lack of activity in our testes."
Sexualized imagery, tight diapers, cell phones?
The study concentrated on three parameters: sperm count per ejaculate, density of sperm per milliliter of ejaculate, and total volume of ejaculate.
In the industrialized western nations, the first two parameters showed significant decline, while the third stayed essentially constant. In other words, the amount of liquid ejaculated remained the same, but the amount of sperm in the western world took the plunge.
What makes this analysis so unique, Schlatt surmises, is that it possibly singles out western lifestyle as responsible for the diminished activity in our sperm production apparatus.
"Maybe western men look too much at naked women during everyday exposure? That would mean that our hypothalamus gets too much input. It could mean that our [diapers] were too tight in our childhood and produced too much heat. It could be that our mobile phones do something to our endocrine or testicular environment that adversely affects the turnover of cells. It could have millions of causes. We don't know."
Schlatt stressed that each of these suppositions was exactly that: mere speculation of causal relationships that have no way of being corroborated at this point in the research.
Tip of the iceberg
Scientists in the field of reproductive medicine have known for years that sperm counts are on the decline. But Artur Mayerhofer, another of Germany's leading voices in the field, says this latest analysis takes the issue much further.
"We've never seen anything so well documented, so methodologically sound," Mayerhofer told DW, adding that it gave rise to potential grounds for concern.
"Not because it means that males in these parts of the world are becoming infertile, but rather because it could explain other trends we've been witnessing, for example, a rise in testicular cancer, male genital birth defects (cryptorchidism), and even the connection with morbidity and mortality," the Munich-based professor said. But he advises extreme caution when making such epidemiological generalizations.
Mayenhofer's apprehension rings with leading author Hagai Levine's summation of the analysis as a "wake-up call" for researchers and health organizations across the world.
But Schlatt struck a more balanced, gender-specific conclusion: "Don't panic! Men in the western world still have around 47 million sperm swimming in one milliliter of ejaculate. That's more than enough for fertility, but it could possibly mean that the western trend of having children later may have another obstacle to contend with: Not for men, though, much more for women."
The study is published in Human Reproduction Update.