What to learn from the study that supports the hypothesis of a global decline in sperm concentration
This study, unveiled Tuesday, follows previous work conducted in the West, complementing it with data collected in Asia, South America and Africa.
For the first time, a study is looking at male fertility on a global scale. And its conclusions, published on Tuesday 15 November in the British journal Human Reproduction Update, are hardly reassuring.
This publication establishes that the quantity of spermatozoa and their concentration have clearly decreased over the last few decades, and this worldwide, which supports the thesis of a decline in male fertility. Here is what you need to know.
Declining sperm counts around the world
By compiling data from some 40 studies previously conducted, including in South America, Asia and Africa, this new publication complements the results obtained by the same team of researchers, led by Israeli epidemiologist Hagai Levine, in 2017.
At the time, the latter had also found a decline in sperm quantity and concentration in the male population, but had limited their research to mainly Western countries, drawing criticism. This analysis is therefore “the first to report a decline in total sperm count and concentration in unselected men” in these continents, the study notes.
A trend that has been accelerating since the beginning of the 21st century
“Sperm concentration has significantly decreased between 1973 and 2018,” summarize the authors of this work. “Moreover, the data suggest that this global decline has continued at an accelerated rate since the beginning of the 21st century,” they write.
In detail, the study reports that sperm concentration has declined globally by 51.6% over a forty-five year period. Models that analyzed only data collected after the year 2000 show a steeper decline, it continues, noting that “the percentage decline per year doubled from 1.16% decline in the post-1972 period to 2.64% after 2000.” The study adds that “similar results were observed for sperm count, which declined by 62.3% in unselected men” whose semen was analyzed. A “considerable and persistent decline now recognized as a public health problem,” the authors write in their conclusions.
Results to be qualified by possible biases
Other researchers, already skeptical of the 2017 study, however, qualified the conclusions of this new publication. “I continue to doubt the quality of the studies, especially the older ones, (…) on which this new analysis is based,” andrologist Allan Pacey told AFP, without questioning the way the authors conducted their compilation. According to him, the evolution of the sperm count could in fact reflect more and more reliable measurement techniques, and not the reality itself.
The study states in its introduction that it is difficult to examine these trends in sperm concentration and quantity in semen, as “there is no systematic collection of these data at this time”. It therefore advocates for the establishment of a multidisciplinary surveillance system with indices to monitor the reproductive health of the population.
The study does not provide any explanation for the decrease in sperm quantity and concentration observed in semen. It calls for “further research into the causes of this continuing decline” and for “an immediate and appropriate response to prevent further disruption to male reproductive health.
Other factors to consider when assessing fertility are
Sperm quantity and concentration are factors that affect male fertility, but not the only ones. Their mobility, which also plays a crucial role, is not measured by this study. This study does not therefore allow us to conclude that there is a general decline in male fertility, even if it provides elements in this direction and is in line with other studies that have examined the causes of this trend.
It is suspected that there are “reasons such as obesity, lack of physical activity, pollution and exposure to chemicals in the environment,” said endocrinologist Channa Jayasena, quoted by the British Science Media Center. This expert from Imperial College London, who was not involved in the study, nevertheless commented that it represented “important” work.
“The important thing to remember is that this is desperately bad news for couples’ fertility,” Professor Richard Sharpe, an endocrinologist at the University of Edinburgh (Scotland), commented for the Science Media Center. He noted that, on a global scale, couples only test their fertility once in their 30s or 40s, when women’s fertility declines compared to their 20s. “If the sperm count is low in his male partner’s semen (…), I call that the perfect recipe for increased infertility” in heterosexual couples.