Men don’t produce as many sperm as they did decades ago. This is a trend seen around the world. The pace of decline is accelerating.
These are the main findings of a new analysis of sperm count studies published Tuesday in the journal Human Reproduction Update. It is the most voluminous report that examines the question.
In a press release, the researchers behind the analysis presented their findings as a “looming crisis” and a “canary in a coal mine” that could “threaten the survival of humanity”.
Shanna Swan, author of the new analysis, said in an interview that the new research should raise alarm bells about men’s overall health and reproductive fitness.
“There is a decline in reproductive function,” said Swan, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai in New York. “This is not an isolated phenomenon.”
Sperm count is an imperfect measure of fertility, and some outside researchers have said they have reservations about the new analysis. But even those critics say the research raises crucial questions about men’s reproductive health — a topic some see as having been neglected by science and ripe for further exploration.
“After decades, we still don’t know much about normal sperm concentrations in men around the world, and to this day, this represents the best effort to take all of the available data and try to piece it together,” he said. said Dr. Bradley Anawalt, reproductive endocrinologist and chief of medicine at UW Medical Center in Seattle.
But Anawalt said the inherent limitations of this type of analysis – which combines results from more than 200 sperm count studies – could lead to misleading conclusions. More research is needed to better understand if sperm concentrations drop so dramatically and what could be causing the problem.
“I wouldn’t want people to think we’re in great danger of imploding as a species,” Anawalt said. “We still have to ask ourselves the question: is this potentially a smoke signal?”
The researchers behind the study first made waves in 2017, when they published a paper showing declining sperm counts in North America, Europe and Australia, places where data was readily available.
This article attracted media attention and sparked scholarly debate, including criticism from a Harvard research group of its narrow geographic scope and the language used to describe the areas studied. According to the Harvard researchers, the document has been used as fodder for wild speculation about men’s health, as well as unfounded and racist theories by some white supremacist and alt-right groups.
“We were challenged by some critics who felt we were only talking about white men, and that was not our intention,” Swan said. “In areas where labs were less available and resources were scarcer, there were fewer studies.”
Swan said more high-quality sperm count studies had been produced since the 2017 paper, and the research group was now able to fill in the geographic gaps.
To assess the world’s sperm count, researchers evaluated hundreds of scientific papers, ultimately combining data and conclusions from 223 previous papers on sperm concentration. The researchers assessed the estimates, which included data on semen samples from 1973 to 2018. The authors tried to control for factors such as age and abstinence time.
The new data, which incorporates studies from around the world, “follows the same trend” as the 2017 study, Swan said. “To our surprise, the pace had picked up. The decline was accentuated. »
Despite the negative trend, the average male sperm count in 2018 remained above levels that the World Health Organization considers normal.
Swan said previous research on small groups of men has linked reduced sperm count to pesticides and chemicals that disrupt the endocrine system.
“I don’t think there is any doubt that these chemicals affect sperm quality. Where there is some doubt is how you analyze how much change is due to lifestyle factors and how much is due to chemicals,” Swan said.
Outside researchers said the new analysis was thorough and conservative, but filtering and combining so many different studies by separate research groups could inevitably lead to bias.
“You combine all kinds of methodologies. You are going to introduce a bias,” Anawalt said. “We have to take this with a bit of a grain of salt.”
Trends in how past research has been conducted or promoted over the decades could skew the overall view of the issue, the researchers said.
It’s possible that medical and scientific journals are more likely to publish results that show declines, said Dr. John Amory, a professor of medicine at the University of Washington who was not involved in the analysis. It’s also possible that the type of men involved in sperm count studies are different from those who weren’t.
Sperm can be difficult to count and characterize accurately, which means numbers can vary from study to study and over time, depending on how the sperm are counted.
“You talk about millions of cells, and they move,” Amory said. “There are other things in the ejaculate that aren’t semen – round cells and debris.”
Also, sperm count is just one factor in determining fertility. Motility — how well 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 worked to limit their effects on the results. They only used studies that counted sperm according to World Health Organization guidelines or used the same techniques, Swan said.
Other studies have shown a drop in other sperm parameters and an increase in the number of men seeking treatment for fertility issues, said Dr. Ryan Smith, associate professor of urology at the University of Virginia, who did not participate in the reanalysis.
“I think the consistency of what’s in the research today is really concerning,” Smith said. “We can’t say anything conclusive at this time, but I think as clinicians and researchers we need to direct research support and advocacy towards this.”
Male fertility can be a strong indicator of overall health.
Men with infertility issues are at increased risk of other diseases, said Amory, who thinks such issues can be warning signs of health issues or alert patients to diseases they didn’t know were there. they affected their lives.
Obesity, opioid use, and other health factors can lead to infertility. Some prescription drugs can have negative effects on fertility.
It is possible that environmental factors and pollution largely affect sperm count.
“Identifying individual culprits is difficult,” Smith said.