Spermatozoa: obesity, chemicals… a study supports the hypothesis of a global decline

The concentration of spermatozoa, one of the factors of male fertility, has decreased significantly across the planet in recent decades, suggests a major study published on Tuesday, November 15.

“The concentration of spermatozoa decreased significantly between 1973 and 2018”, summarize the authors of this work, published in the journal Human Reproduction Update and carried out by compiling about forty preliminary studies.

This publication is on an unprecedented scale on the subject, although it confirms the conclusions of a previous study by the same team, led by Israeli epidemiologist Hagai Levine.

This one, published in 2017, had been the subject of several criticisms, especially because its conclusions only concerned certain countries, all of which belong to the Western world.

This time, after integrating more data, the authors can conclude that the downward trend also concerns South America, Asia and Africa.

“Furthermore, the data suggest that this global decline has continued at an accelerating rate since the beginning of the 21st century,” they write.

The amount of spermatozoa is one of the factors that play on male fertility, but it is not the only one. Their mobility also plays a crucial role, which is not measured in this study.

This therefore does not allow us to conclude that there is a general decline in male fertility, although it provides elements in this direction and is in line with other work which has rather investigated the causes of this trend.

What are the reasons?

One therefore suspects “reasons such as e.g obesity, lack of physical activity, pollution and exposure to chemicals in the environment“, recalled endocrinologist Channa Jayasena.

This Imperial College expert, who was not involved in the study and spoke to the British Science Media Center, welcomed the “important” work in this case.

Other researchers, already skeptical of the 2017 study, qualified the conclusions of this new publication, believing that it did not address all the shortcomings of the previous one.

“I continue to doubt the quality of the studies, especially the oldest ones, (…) on which this new analysis is based,” andrologist Allan Pacey told AFP, without questioning the way the authors carried out their compilation.

According to him, the evolution of sperm could actually reflect increasingly reliable measurement techniques and not reality itself.

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