The quality of sperm in U.S. men has been decreasing over the last 15 years, according to an analysis, and although it’s unclear what is causing it, there are a few environmental factors that could be a factor.

Discussion of declining sperm count is not new. In 2017, the subject was a hot topic following a massive study that found that the sperm count of western males fell by over 50% between 1973 and 2011. The study called for a swift inquiry into the reasons for this decrease, but the study received some criticism.

The most current long-term study has put the sperm under the microscope yet again.

The study looked at the semen of donors across nine regions of the U.S. between January 2005 until April 2021.

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

Examining the sperm samples, the researchers examined four primary factors: ejaculate volume average concentration, motility–the capacity of sperms to swim the correct way, and total motile count.

The study revealed that based on three of these parameters, the high-quality in U.S. sperm had fallen dramatically. Motility, average concentration and the total motile sperm count had all declined during the study’s 16 years with the exception of Spokane which was deemed to be insignificant due to the lack of donors. Indianapolis saw a decline in motility and concentration Sperm, but an improvement in the amount of motility. The volume of ejaculate was not reduced substantially.

The study is presented in collaboration with co-author Chelsea Canon, a fertility expert from the Icahn School of Medicine at Mount Sinai in New York City in the American Society for Reproductive Medicine conference in Baltimore this week.

According to the research they aren’t sure what caused the sperm’s quality decrease, but it is observed that lifestyle and environmental elements have been implicated in declining sperm quality before.

On August 1, 2001 a research released in Human Reproduction looked at 225 males who were involved in relationship in the Litoral Sur region of Argentina which was described as one of the highest-yielding agriculture regions of this world in the year. The participants had been to an infertility consult between 1995 to 1998.

Researchers questioned individuals about exposures to chemicals in the last decade. Based on the sperm samples of the participants, they discovered that exposure to solvents and pesticides specifically was linked to “dramatic changes” in semen characteristics.

“The use of these agents has increased substantially since the 1940s, due to industrial and agricultural activities,” the study stated, “and Argentina has become a major user of pesticides.” The study acknowledged that it can not completely rule out the possibility that there is selection bias.

In the meantime, Shanna Swan, a different Ichan School of Medicine fertility researcher, and the principal writer of the fad western male study on sperm count has been vocal about the possible effects of environmental pollution on sperm count.

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An interview she conducted with Salon in April of this calendar year Swan identified phthalates as being potentially harmful to Sperm. Swan said that people get exposed to these substances which make plastics robust, frequently because of pesticides found in fooditems, cleaning products, as well as in everyday household products like shower curtains or any other soft plastic.

She said the fact that “these chemicals have a direct action on the steroid hormones,” although some studies haven’t been conclusive. It is the U.S. Centers for Disease Control and Prevention declares it is “more research is needed to assess the human health effects of exposure to phthalates.”