Men don’t have as much sperm as they did decades ago. It is a trend that has been observed across the globe. The pace of decline is accelerating.
Those are the main findings of a new analysis of sperm count studies published Tuesday in the journal Human Reproduction Update. It is the largest report to examine the issue.
In a news release, the researchers behind the analysis framed their findings as a “looming crisis” and a “canary in the coal mine” that could threaten the “survival of humanity”.
Shanna Swan, the author of the new analysis, said in an interview that the new research should sound the alarm about the overall health and reproductive well-being of men.
“Reproductive function is declining,” said Swan, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai in New York City. “This is not an isolated phenomenon.”
Sperm count is an imperfect measure of fertility, and some outside researchers expressed concern about the new analysis. But even those critics say the research raises important questions about men’s reproductive health — a topic that has been viewed by some as neglected by science and ripe for more thorough examination.
“After all these years, we still don’t know much about normal sperm concentrations in men around the world, and so far this is the best attempt to take all the available data out there and try to put them together,” said Dr. Bradley Anawalt, a reproductive endocrinologist and chief medical officer at UW Medical Center in Seattle.
But Anawalt said the inherent limitations of this type of analysis – which combined results from more than 200 sperm count studies – could lead to misleading conclusions. More research is needed to better understand whether there is such a reduction in sperm concentration and what could be behind the issue.
“I don’t want people to think we’re in dire straits as a species,” Anawalt said. “One still has to ask the question: Is this a possible smoke signal?”
The researchers behind the study first made waves in 2017, when they published a paper showing falling sperm counts in North America, Europe and Australia – places where data was readily available.
That paper received significant media attention and sparked scientific debate, including criticism from a Harvard research group for its narrow geographic focus and the language it used to describe the areas studied . Some white supremacist and alt-right groups used the paper as fodder for wild speculation about men’s health, as well as baseless and racist theories, according to Harvard researchers.
“We were challenged by some critics who felt that we were only talking about white men, and that was not our intention,” Swan said. “In areas where there were fewer laboratories available and where resources were scarce, there were fewer studies.”
Swan said more high-quality sperm count studies have been done since the 2017 paper and the research group was now able to fill in the geographic gaps.
To assess sperm counts around the world, the researchers evaluated hundreds of scientific articles, ultimately compiling the data and findings of 223 previous articles about sperm concentration. The researchers evaluated the estimates, which included data on semen samples from 1973 to 2018. The authors tried to control for factors such as age and time of abstinence.
The new data, which included studies from around the world, “followed the same trend” as the 2017 study, Swan said. “To our surprise, the pace was faster. The decline got steeper.”
Despite the negative trend, the average sperm count for men in 2018 remained higher than the levels considered normal by the World Health Organization.
Swan said previous research on small groups of men had linked sperm count declines to pesticides and chemicals that disrupt the endocrine system.
“I don’t think there is any doubt that these chemicals affect the quality of semen. When in doubt is how you parse how much change is due to lifestyle factors and how much is due to chemicals,” said Swan.
Outside researchers said the new analysis was thorough and careful, but that sifting and combining so many different studies by separate research groups could lead to biases.
“You’re combining all kinds of methodologies. You’re going to introduce bias,” Anawalt said. “We have to take this with a grain of salt.”
Trends in how previous research was conducted or promoted over many years could skew the overall perception of the issue, researchers said.
Medical and scientific journals are more likely to publish results that show decline, said Dr. John Amory, a professor of medicine at the University of Washington who was not involved in the analysis. It is also possible that the type of men involved in sperm count studies is different from the men who were not.
Sperm can be difficult to accurately count and characterize, meaning that numbers can vary from study to study and over time, depending on how sperm are counted.
“You’re talking about millions of cells, and they’re moving,” Amory said. “There are other things in the ejaculate that are not sperm – round cells and debris.”
Besides, sperm count is only one factor in determining fertility. Motility — how effectively sperm can swim — and morphology — the size and shape of sperm — are also important indicators of male fertility, Amory said.
The authors of the new analysis acknowledged these limitations and tried hard to limit their effects on the outcome. They only used studies that counted sperm according to World Health Organization guidelines or used the same techniques, Swan said.
Other studies have shown decreases in other sperm parameters and an increase in the number of men seeking treatment for fertility issues, said Dr. Ryan Smith, an associate professor of urology at the University of Virginia, who was not involved in the new analysis.
“The consistency of what’s being found in the research today is definitely a concern,” Smith said. “We can’t say anything conclusive right now, but I think, as clinicians and researchers, we need to focus research support and advocacy on that.”
Male fertility can be a strong indicator of general health.
Men with infertility problems are at greater risk of other diseases, said Amory, who believes those issues can cause health problems or alert patients to diseases they didn’t realize they had. disrupt their lives.
Obesity, opioid use and other health factors can drive infertility. Some prescription medications can have a negative effect on fertility.
It is possible that environmental factors and pollution may be affecting sperm count in general.
“Identifying individual culprits is challenging,” Smith said.
This article was originally published on NBCNews.com