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Add falling sperm counts to the list of threats to human survival, epidemiologist warns

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Humanity is facing not only a coronavirus pandemic and a climate crisis, but its existence is also threatened by falling sperm counts because of chemical exposures, a prominent epidemiologist warns in a new book.

"Chemicals in our environment and other lifestyle factors in our modern age have harmed our reproductive health to the extent that, in the future, it may not be possible for most people to reproduce in the old-fashioned way," said Shanna Swan, an environmental and reproductive epidemiologist at the Icahn School of Medicine at Mount Sinai in New York with more than four decades of experience in the field.

Sperm counts among men in North America, Europe, Australia and New Zealand declined more than 59% from 1973 to 2011, according to a meta-analysis Swan co-wrote in 2017. At the current rate, half of men in those countries would have no sperm by 2045, while many others would have very low counts, Swan told USA TODAY.

"Some of what we’ve been thinking of as fiction, from stories such as 'The Handmaid’s Tale' and 'Children of Men,' is rapidly becoming reality," Swan writes in her new book with science writer Stacey Colino out this week, "Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race."

In the book, Swan argues that chemicals pervasive in our world are interfering with the hormones in our bodies and contributing to harmful reproductive health outcomes in men and women. These "endocrine-disrupting chemicals" include chemicals that are water-soluble and wash out of our bodies, such as phthalates and bisphenol A (BPA), as well as "forever chemicals" that do not degrade, such as perfluoroalkyl substances (PFAS).

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The chemicals enter our bodies through foods and drink, microscopic airborne particles we inhale, and in the products we absorb through our skin, Swan said. They're found in plastic and vinyl, floor and wall coverings, medical tubing and medical devices, children's toys, nail polishes, perfumes, hair sprays, soaps, shampoos and more.

Phthalates, for example, are commonly consumed through foods, she said.

"They’re added to plastic to make them soft and squishy – think shower curtains, rubber duckies, soft tubing. The processed food we eat passes through soft tubing to get into its packaging. When these chemicals in the plastic come in contact with food, the phthalates leave the plastic and leach into the food. When we eat the food, they get into our bodies," she said.

Endocrine-disrupting chemicals can interfere with hormones in several different ways. Phthalates may "trick the body" into thinking it has more testosterone than it actually does, causing the body to stop producing testosterone and increasing the chances the man will be infertile or have a lower sperm count, Swan said.

Dr. Pat Hunt, a geneticist at the Washington State University School of Molecular Biosciences, has been studying the effect of chemical exposures on male and female fertility since a laboratory accident in 1998 alerted her to the harmful effects of household products.

"Over the years, I've watched the opinions of my scientific colleagues change as the evidence has become increasingly convincing," Hunt said. "There’s no question that sperm counts have fallen. The hypothesis that sperm counts have fallen due to exposure to these chemicals has also gained more and more credence."

Some trade groups, however, question the connection between endocrine-disrupting chemicals and adverse health outcomes, and some scientists have criticized studies for a lack of evidence demonstrating a direct causation between the two.

Vinyl Verified, an organization working to promote public perception of vinyl, writes on its website that "a select number of competitive interests and agenda-driven activists have advanced a dishonest campaign to mislead consumers, and deny them their right to make their own decisions about vinyl."

And some scientists question whether sperm counts are falling at all. Allan Pacey, a professor of andrology at Britain’s University of Sheffield, said that while he believes prenatal exposure to endocrine-disrupting chemicals can affect male fetal development, he remains "unconvinced by the data which suggests that sperm counts have fallen worldwide because of this."

"I think science and medicine has accepted this hypothesis uncritically," Pacey said. "Extraordinary claims generally require extraordinary evidence – however, apparently not in this case."

Pacey takes issue with the way scientists have reached their conclusions – by conducting retrospective analyses of semen analysis data performed in the past. Pacey said this method of analysis is "weak" because the methods of laboratory andrology, such as training, have changed over time.

The 2017 study Swan co-wrote was "an improvement" because it used more control measures, but the study still not did present "extraordinary evidence," Pacey said. "I cannot prove this, but neither can they."

Linda Birnbaum, former director of the National Institute of Environmental Health Sciences as well as the National Toxicology Program, said the 2017 study was "impressive" and noted Swan's work also draws on studies in animals, boys and young men.

"There are repeated studies by different investigators in different locations that support that sperm counts are falling," Birnbaum said. "It’s complex what might be causing it. I don’t think there’s any one thing. But I do think endocrine-disrupting chemicals  one part of the puzzle."

'People are not choosing to lower their sperm count'

Worldwide fertility dropped by 50% from 1960 to 2015, Swan writes. She acknowledges a host of socioeconomic factors are contributing to the decline, such as people choosing to have children later in life and having smaller families.

But what's surprising is that fertility is dropping across age groups, Swan writes. Not only are sperm counts in men gradually declining, but boys are also seeing higher rates of genital abnormalities. Among women, the risk of miscarriage has been rising across all ages.

"Part of this picture has an element of choice in it, and part of it doesn’t," Swan said. "People are not choosing to lower their sperm count."

Lifestyle factors – including diet, physical activity, smoking and alcohol or drug use – can alter hormone levels and are playing a role in the decline, Swan said. But Swan said she's most concerned about chemical exposures, particularly for pregnant women and children.

"The other lifestyle factors matter in a transient way," Swan said. "The reason I’m so focused on these early exposures to endocrine disruptors is because that’s never going to change, and it’s going to be passed on to later generations. They’re much more important to the story, although they’re much less easy to control."

Endocrine-disrupting chemicals don't just affect reproductive health. They have also been linked to "numerous adverse health effects in almost all biological systems," including the immunological, neurological, metabolic and cardiovascular systems, Swan writes.

"We can see tiny changes during development that, in an adult, can increase the rate of cancers," Hunt said. "We’re setting up our children to have metabolic problems as adults, and I find that incredibly sobering and worrying."

And we're not just hurting ourselves. We're harming animals, too.

"These ubiquitous environmental chemicals have taken a toll on the animal kingdom in many different ways," Swan writes. "As a species, we’re failing to propagate and repopulate ourselves, and we’re hindering the ability of other species to do so."

Remove, replace and regulate

In her book, Swan lays out an action plan to help people change their daily habits and reduce exposures. Instead of the traditional "three Rs" typically touted to promote reducing exposure to plastics and other environmental chemicals, Swan suggested promoting three new ones: "Remove, replace and regulate" endocrine-disrupting chemicals.

"The chemicals themselves have to be remodeled – substituted for chemicals that cannot interfere with human hormone systems. That’s absolutely critical," Swan said. "They have to not be harmful at very low doses. And they have to not be persistent in the environment."

Hunt said her research on the effects of endocrine-disrupting chemicals has caused her to think about life "completely differently."

"You can’t possibly eliminate plastics from your life, but you can buy different products," Hunt said. "The plastics in my kitchen are silicone, and I use a lot of glass. There’s a rule in my house that plastics of any sort don’t go into the dishwasher and never go into the microwave. And I read labels obsessively."

Swan also calls for much larger, societal changes, including greater government regulation of chemicals.

"We need to rethink our whole approach to chemical safety," Hunt said. "We place the onus right now on federal regulatory agencies to demonstrate that these chemicals are harmful. The onus should be on demonstrating that they’re safe before they go into use, not demonstrating that they’re dangerous after they go into use."

Swan said that for decades the U.S. has gone through cycles of public outcry about particular chemicals, such as BPA, only to replace the chemical with ones that are also harmful.

"This is a practice we call regrettable substitution, or, informally, whack-a-mole. You knock down one bad chemical for another one that has a new name but does the same thing," she said.

Swan said she is launching a campaign tied to the book to educate the general public, along with the medical community, about the dangers of endocrine-disrupting chemicals. Swan said she hopes to reach communities of color in particular, because many are disproportionately affected by the chemicals.

"Communities of color are differentially overexposed, for example, by decreased availability of fresh, unprocessed foods and their proximity to poorer air and water quality," Swan said. "These communities have higher exposure and experience a higher impact from these chemicals. There’s an equity issue here."

'These things are not separate'

Swan said the discussion around the reproductive health crisis in 2021 is comparable to where the discussion around climate change was 40 years ago. "Initially there was denial, and gradually people began to accept that this was a problem," Swan said.

In 1992, when a paper in the British Medical Journal suggested sperm counts had gradually declined over the past five decades, the paper "was not taken seriously. It was criticized and pretty much ignored," Swan said. But in 2017, when Swan co-wrote the meta-analysis reaching the same conclusion, the paper became one of the most-referenced scientific papers worldwide that year.

"Where they had denied the problem in 1992, they were saying yes, it’s a problem," she said. "Now, we need to move on to the next phase where we take responsibility as a society, as a planet."

Swan said discussions of reproductive health should be included in discussions surrounding climate change and COVID-19. Many endocrine-disrupting chemicals, for example, are made from petroleum-producing byproducts. Moreover, recent papers have also shown that chemical exposures increase the risk of severe disease from COVID-19.

"These things are not separate, and I think they should be considered together," Swan said. "We have to recognize that we have a trifecta of risks coming down on us."