American Men, Your Sperm Is Getting Worse and Scientists Don't Know Why

Sperm quality in U.S. men has been falling over the past 15 years according to a study, and while it's not entirely clear why, environmental factors may be playing a part.

Talk of declining sperm is nothing new. Back in 2017 the topic made global headlines after a huge study concluded that sperm counts in western men had fallen by over 50 percent between 1973 and 2011. It called for an urgent investigation into the causes of this decline—though the study also faced some criticism.

Now, a more recent long-term investigation has put sperm in the spotlight once more.

The study examined semen samples from sperm donors across nine different regions in the U.S. between January 2005 and April 2021.

In total, 176,706 sperm samples were supplied by 3,532 men aged between 19 and 38 from Palo Alto, Los Angeles, Westwood, International Nordic Cryo Bank Denmark, Indianapolis, Cambridge, New York, Houston and or Spokane.

Analyzing the sperm samples, the researchers looked at four main criteria: ejaculate volume, average concentration, motility—the ability of sperm to swim the right way—and total motile count.

The researchers found that according to three of these criteria the quality of U.S. sperm had fallen significantly. Average concentration, motility, and total motile sperm count all fell over the 16-year study period, apart from in Spokane, which was discounted due to a lack of donors. Indianapolis showed a decrease in concentration and total motile sperm but an increase in motility. Ejaculate volume did not decrease significantly.

The research was presented by co-author Chelsea Canon, a fertility expert at the Icahn School of Medicine at Mount Sinai in New York City, at the American Society for Reproductive Medicine conference in Baltimore last week.

According to the researchers, it's not clear what caused the sperm quality decline but it's noted that environmental and lifestyle factors have been implicated in sperm decline before.

In August 2001, a study published in the journal Human Reproduction looked at 225 males in relationships in the Litoral Sur region of Argentina, described as one of the most productive farming regions in the world at the time. The men had attended an infertility consultation between 1995 and 1998.

The researchers asked the men about their exposure to chemical substances over the past decade. Based on sperm samples from the men, they found that environmental exposure to pesticides and solvents in particular was associated with "dramatic changes" in semen characteristics.

"The use of these agents has increased substantially since the 1940s, due to industrial and agricultural activities," the study noted, "and Argentina has become a major user of pesticides." The study acknowledged it could not exclude the possibility of selection bias.

Meanwhile Shanna Swan, another Ichan School of Medicine fertility researcher and a lead author of the popular 2017 western men sperm count study, has long spoken of the potential effects of environmental pollutants on sperm count.

In an interview with Salon in April this year, Swan described phthalates in particular as potentially harmful to sperm. She noted that humans are exposed to these chemicals, which make plastics more durable, regularly due to pesticides in food, in cleaning products, and in day-to-day household items like shower curtains or any soft plastic.

She noted that "these chemicals have a direct action on the steroid hormones," though other studies have been less conclusive. The U.S. Centers for Disease Control and Prevention states that "more research is needed to assess the human health effects of exposure to phthalates."

Sperm cells
A stock image of a 3D illustration of sperm cells swimming. Sperm quality has been declining in men over the past few decades according to some studies. Rost-9D/Getty