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Count Down

How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race

About The Book

In the tradition of Silent Spring and The Sixth Extinction, an urgent, “disturbing, empowering, and essential” (Kirkus Reviews, starred review) book about the ways in which chemicals in the modern environment are changing—and endangering—human sexuality and fertility on the grandest scale, from renowned epidemiologist Shanna Swan.

In 2017, author Shanna Swan and her team of researchers completed a major study. They found that over the past four decades, sperm levels among men in Western countries have dropped by more than 50 percent. They came to this conclusion after examining 185 studies involving close to 45,000 healthy men. The result sent shockwaves around the globe—but the story didn’t end there. It turns out our sexual development is changing in broader ways, for both men and women and even other species, and that the modern world is on pace to become an infertile one.

How and why could this happen? What is hijacking our fertility and our health? Count Down unpacks these questions, revealing what Swan and other researchers have learned about how both lifestyle and chemical exposures are affecting our fertility, sexual development—potentially including the increase in gender fluidity—and general health as a species. Engagingly explaining the science and repercussions of these worldwide threats and providing simple and practical guidelines for effectively avoiding chemical goods (from water bottles to shaving cream) both as individuals and societies, Count Down is “staggering in its findings” (Erin Brockovich, The Guardian) and “will serve as an awakening” (The New York Times Book Review).


Chapter 1: Reproductive Shock: Hormonal Havoc in Our Midst 1 Reproductive Shock: Hormonal Havoc in Our Midst The Spermageddon Scare
In late July 2017, it seemed as if every media outlet around the globe had become obsessed with the state of human sperm counts. Psychology Today cried, “Going, Going, Gone? Human Sperm Counts Are Plunging,” while the BBC declared, “Sperm Count Drop Could Make Humans Extinct,” and the Financial Times announced, “?‘Urgent Wake-Up Call’ for Male Health as Sperm Counts Plummet.” A month later, Newsweek published a major cover story on the same subject: “Who’s Killing America’s Sperm?”

By the end of the year, my scientific paper “Temporal Trends in Sperm Count: A Systematic Review and Meta-Regression Analysis,” which sparked these stories—and hundreds of others around the world—was ranked number 26 among all referenced scientific papers published worldwide, according to Altmetric’s 2017 report.

This truly was the drop heard round the world.

These days, the world as we’ve known it feels as though it’s changing at warp speed. The same could be said for the status of the human race. It’s not only that sperm counts have plummeted by 50 percent in the last forty years; it’s also that this alarming rate of decline could mean the human race will be unable to reproduce itself if the trend continues. As my study collaborator Hagai Levine, MD, asks, “What will happen in the future—will sperm count reach zero? Is there a chance that this decline would lead to extinction of the human species? Given the extinction of multiple species, often associated with man-made environmental disruption, this is certainly possible. Even if there is low probability for such a scenario, given the horrific implications, we have to do our best to prevent it.”

This is especially worrisome because the sperm-count decline that’s occurring in Western countries is unabating; it’s steep, significant, and continuing, with no signs of tapering off. As Danish researcher and clinician Niels Skakkebaek, MD, who was the first person to alert the scientific community to the role of environmental factors in sperm decline, said, “It’s an inconvenient message, but the species is under threat, and that should be a wake-up call to all of us. If this doesn’t change in a generation, it is going to be an enormously different society for our grandchildren and their children.” Indeed, if the decline continues at the same rate, by 2050 many couples will need to turn to technology—such as assisted reproduction, frozen embryos, even eggs and sperm that are created from other cells in the laboratory (yes, this is actually being done)—to reproduce.
A Dystopian Future?
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. In the winter of 2017, I presented my sperm-decline findings at the One Health, One Planet conference, which focused on the interconnected health of different species on the planet, the damage being inflicted by our mad “industrialization” of the environment, and its devastating effects on frogs, birds, polar bears, and other species. After presenting the results of our analysis, which were shocking enough to the audience, I spoke for the first time about what sperm decline could mean for Homo sapiens. That night, I awoke from a dream, feeling incredibly anxious as I suddenly realized the full implications of the story I’d put together—that given the declines in sperm count and testosterone levels and the increases in hormonally active chemicals that are being spewed into the environment, we really are in a dangerous situation for mankind and world fertility.

This was no longer only a matter of scientific study for me. I felt and remain genuinely scared by these findings on a personal level.

In some ways, the picture looks even worse when you delve deeper because it’s not just an issue for men. Women, children, and other species are also having their reproductive development and function commandeered in a dysfunctional direction. In some countries throughout the world, including the United States, a massive sexual slump is underway, due to declines in people’s sex drives and interest in sexual activity; men, including younger guys, are also experiencing greater rates of erectile dysfunction. In animals, there have been changes in mating behavior, with more reports of male turtles humping other male turtles, and female fish and frogs becoming masculinized after being exposed to certain chemicals.

Taken together, these trends are causing scientists and environmentalists to wonder, How and why could this be happening? The answer is complicated. Though these interspecies anomalies may appear to be distinct and isolated incidents, the fact is that they all share several underlying causes. In particular, the ubiquity of insidiously harmful chemicals in the modern world is threatening the reproductive development and functionality of both humans and other species. The worst offenders: chemicals that interfere with our body’s natural hormones. These endocrine-disrupting chemicals (EDCs) are playing havoc with the building blocks of sexual and reproductive development. They’re everywhere in our modern world—and they’re inside our bodies, which is problematic on many levels.

Here’s why: Hormones—particularly, two of the sex hormones, estrogen and testosterone—are what make reproductive function possible. Both the amount of each hormone and the ratio between these hormones are important for both sexes. The sweet spots for these ratios are different for each sex: depending on whether you are a man or a woman, your body needs optimal amounts of estrogen and testosterone, not too much or too little of either one. To make it more complicated, the timing of their release can alter reproductive development and functionality, and the transport of hormones can be an issue as well—if they don’t get to the right place at the right time, essential processes such as sperm production or ovulation won’t be set into motion. Endocrine-disrupting chemicals, as well as lifestyle factors—including diet, physical activity, smoking, and alcohol or drug use—can alter these parameters, sending levels of these crucial hormones in the wrong direction.
High-Altitude Worries
Another, no less important or complicated, question, is, What do these reproductive changes mean for the fate of the human race and the future of the planet? It’s not just a matter of survival—whether humans will continue to be able to reproduce or whether the human race will die out in a Children of Men–type scenario. These issues have subtler, more personal consequences as well. Take declining sperm counts: statistically, this phenomenon goes hand in hand with many other problems for males, including an increased risk for cardiovascular disease, diabetes, and premature mortality (you’ll learn more about these downstream health hazards in chapter 8).

And again, this isn’t just about men. Not only is women’s fertility being affected, even if less obviously or dramatically, but sperm quality can be altered by changes that occur when male fetuses are in the mother’s womb. At that time the fetus is affected by the mother’s choices and habits, which means that women can serve as conduits for potentially harmful chemical exposures. Contrary to previous belief, the womb does not protect the fetus against chemical assault, and a developing fetus has few defenses against the infiltration of chemicals. Looked at another way, the most important events in a male’s life, in terms of sexual and reproductive development, occur while he’s still in utero. Babies and children are more vulnerable to these chemical assaults than adults, but those who are most vulnerable haven’t been born.

The sperm decline signals changes that affect everybody.

As some population experts and scientists put it, “a demographic time bomb” is on the horizon—future generations won’t be able to meet the financial and caretaking needs of an ever-increasing number of older adults and retired workers, given the declining fertility rate. And the changes in sexual development taking place all over the world appear to have been accompanied by an apparent rise in gender fluidity,I which is not a negative development, in my opinion. The point is, human sexuality and society are in flux, and this flux affects us all. It’s as if the snow globe has been shaken, altering the reproductive landscape inside—only this is happening in real life.

What comes to mind when you see a reference to the “1 percent effect,” a common phrase in the cultural lexicon? Most people think of socioeconomic status, namely a ranking in the top 1 percent of wealth in the United States. Not me. I think of the fact that the rate of adverse reproductive changes in males is increasing by about 1 percent per year. This includes the rates of declining sperm counts and testosterone levels, increasing rates of testicular cancer, and the projected worldwide increase in the prevalence of erectile dysfunction. On the female side of the equation, miscarriage rates are also increasing by about 1 percent per year. A coincidence? I think not.
Questioning the Issues
If you’re skeptical about all this, that’s fair enough. I used to be, too. Whether it’s because I’m a trained scientist or a natural-born skeptic, I’ve always been a firm believer in Albert Einstein’s assertion that “blind belief in authority is the greatest enemy of truth.” That axiom has underscored all of my research on environmental influences on human health—including the effects of endocrine-disrupting chemicals, water contamination, and drugs—as well as my interpretation of other people’s research. So when the British Medical Journal published a study in 1992 that claimed worldwide sperm counts had fallen significantly in the previous fifty years—which was a major bombshell—I found the issue intriguing, but I had significant doubts about the validity of the results.

After reading and rereading what came to be known as the Carlsen paper—named after lead author Elisabeth Carlsen—I was among the skeptics who questioned the methodology and the selection of samples, and I thought of many potential biases that might have distorted the findings. Granted, I was hardly alone; numerous critiques and editorials ensued. But the findings of that study were so important from a public health perspective that I couldn’t put them out of my mind, even though I was busy doing research about the risk of birth defects and miscarriage from solvents in drinking water. Doubtful as I was about the findings of that particular study, I knew that certain environmental chemicals could be decreasing sperm counts, so I wanted to investigate; it felt like a bit of a detective case.

In 1994, I was appointed to the National Academy of Sciences Committee on Hormonally Active Agents in the Environment, and soon after, I was asked to tell the committee whether the Carlsen paper’s conclusions were justified. For six months, I combed the literature to find all the criticisms that had been raised about the paper, then I reviewed the sixty-one studies the Carlsen team had included in its analysis to try to address those criticisms. Particular questions I pursued included: Did the early studies include healthier, younger men than the later ones did? Did the later studies include more smokers or obese men, which would create a distorted picture of what was happening? Had the method of counting sperm changed over fifty years in a way that made more recent sperm counts lower?

To get to the bottom of this mystery, I found two colleagues, Laura Fenster and Eric Elkin, who were willing to help me. The results were utterly astounding: after six months of data crunching and considering potential biases and confounding factors, our overall conclusion agreed, almost exactly, with that of the Carlsen team. Because we’d accounted for geographic location in the various studies, we found that sperm counts really were declining in the United States and Europe. But what about the rest of the world?

After these findings were published in 1997, I felt that we needed to ask whether sperm counts were different in different locations, since that would point to environmental factors at play. I’ve spent the last twenty years basically trying to answer that question. After conducting many more studies on semen quality, sperm decline, and related factors, I feel that I have. Not only have I shifted from being dubious to being utterly convinced that a dramatic decline in sperm counts is occurring, I’ve also discovered that various lifestyle factors and environmental exposures may be acting in tandem or in a cumulative fashion to fuel the decline.

Fast-forward to the summer of 2017 when my latest paper on this subject, written with my colleague Hagai Levine and five other committed researchers, went viral.

The news my colleagues and I reported in our meta-analysis: Between 1973 and 2011, sperm concentration (the number of sperm per milliliter of semen) dropped more than 52 percent among random men in Western countries; meanwhile, the total sperm count fell by more than 59 percent. We came to these conclusions after examining the findings from 185 studies involving 42,935 men that had been conducted during this thirty-eight-year period. To be clear: these men weren’t selected based on their fertility status; they were everyday Joes and Johns, ordinary men.

Given that the findings pertain primarily to Western countries, this may sound like a first-world problem, but it’s not. Rather, I suspect that societies in which people are likely to begin having children at a younger age are less likely to be affected by the fertility-damaging effects of environmental chemicals and life stressors. In our meta-analysis, there were much less data on sperm counts from men from South America, Asia, and Africa; however, more recent research reports declines in those regions as well.
Taking This Personally
What does all this mean in relatable terms? When people hear about these threats to their fertility, it’s a big blow to their egos, their sense of potency, and their confidence in being able to sustain themselves as a family, a culture, and a species. It’s startling and chilling when you realize that the number of children you may be capable of having is slightly less than half of that your grandparents could conceive. It’s also shocking that in some parts of the world, the average twentysomething woman today is less fertile than her grandmother was at thirty-five.

The precipitous drop in sperm counts is an example of a “canary in the coal mine” scenario. In other words, the sperm-count decline may be Mother Nature’s way of acting as a whistleblower, drawing attention to the insidious damage human beings have wrought on the built and natural worlds.

Which leads to a third, crucial question about all this: What can we do about the problem? There are steps we can take both as individuals and as a society to stay healthy and protect our sexual development. But the first thing we have to do is learn more about the nature of these problems. Most people outside the scientific community are totally unaware of these disturbing trends, and as a researcher who is committed to identifying environmental causes of reproductive health problems, I feel it’s my duty to draw attention to them.

Whether it’s through our lifestyles or the chemical contaminants we’ve brought into the world, we, as human beings, have inadvertently unleashed these problems. At this rate, it’s hard to know what the future will look like, unless we take conscious and considered steps to protect ourselves and curb the chemicals that are infiltrating our daily lives. The time has come for us to stop playing Russian roulette with our reproductive capacities.

I. Many countries are experiencing increases in issues related to gender identity, gender fluidity, and gender dysphoria. Gender dysphoria refers to the feeling that one’s emotional and psychological identity as male or female is out of sync with one’s biological sex. (You’ll read more about this in chapter 4.)

About The Authors

Photograph by Axel Dupeux

Shanna H. Swan, PhD, is an award-winning scientist based at Mt. Sinai and one of the leading environmental and reproductive epidemiologists in the world. Dr. Swan has published more than 200 scientific papers and has been featured in extensive media coverage around the world. Her appearances include ABC NewsNBC Nightly News, 60 Minutes, CBS News, PBS, BBC, PRI Radio, NPR, and The Joe Rogan Experience as well as in leading magazines and newspapers, including Newsweek, The Washington Post, USA TODAY, Time, US News & World Report, The GuardianBloomberg NewsNew York PostChicago TribuneDaily News (New York), Los Angeles Times, HuffPost, Daily Mail (London), New Scientist, Mental FlossMother JonesNew Telegraph, Euronews, and the National Post.

Photograph by Scott Robinson

Stacey Colino is an award-winning writer specializing in health and psychological issues. Her writing has appeared in US News & World ReportThe Washington PostNewsweek, ParadeNational Geographic, and more. She is the coauthor of numerous books, including Count Down, Emotional Inflammation, and Disease Proof. Stacey is a lifelong dog lover and has owned three rescue dogs. Follow her on X @ColinoStacey.

Product Details

  • Publisher: Scribner (March 31, 2022)
  • Length: 304 pages
  • ISBN13: 9781982113674

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Raves and Reviews

Longlisted for the 2022 PEN/E.O. Wilson Literary Science Writing Award

New York Times Book Review Editors' Choice

“If you’ve smugly enjoyed the dystopian worlds of The Handmaid’s Tale (where infertility is triggered in part by environmental pollutants) or Children of Men (where humanity is on the precipice of extinction)—and believed that these stories were rooted firmly in fantasy—Shanna Swan’s Count Down will serve as an awakening….[It] chronicles rising human infertility and warns of dire consequences for our species if this trend doesn’t slow….An important book for anyone concerned about the environment, pollution, successful childbearing or declining health of the human species.”
New York Times Book Review

"Swann’s book is staggering in its findings….The rapid death and decline of sperm must be addressed, and it must be addressed now. There simply is no time to lose.”
—Erin Brockovich, The Guardian

"An alarming compendium of research. . .the book is full of solid science, with detailed, clear explanations and proposals for how to reduce the harm caused by common chemicals."
New York Review of Books

"An urgent examination of a global problem that requires vastly more attention than it currently receives....The author’s passion for her work and access to reams of alarming data make for riveting reading, and her writing is crisp and unfettered by jargon....With an advocate’s verve and a scientist’s informed confidence, the author voices 'a clarion call for all of us to do what we can to safeguard our fertility, the fate of mankind, and the planet.' An eye-opening, disturbing, empowering, and essential text."
Kirkus Reviews (starred review)

“A convincing plea for heightened awareness of rising reproductive jeopardy and the imperative of eliminating environmental toxins makes this book both alarming and crucial.”
Booklist (starred review)

“[A] thought-provoking look at the state of human reproductive health….This accessible and shocking account succeeds as an eye-opening wake-up call.”
Publishers Weekly

“Grounded in irrefutable science and laced with dry, engaging wit, this epic book asks monumental questions: Has humanity entered into a fertility death spiral? If so, why is it happening, how far will it go, and when will it peak? Finally, what can and must be done? If you dream of children, grandchildren and generations beyond, you must read this book.”
—Pete Myers, PhD, coauthor of Our Stolen Future

“An essential book for this moment….There are a lot of surprises here, including that testosterone therapy decreases sperm counts, and that moms’ exposure to common chemicals during pregnancy alters masculinization of the offspring as well as long-term fertility…. I sincerely hope that everyone reads Count Down—the younger the better—so that they'll have the chance to preserve their fertility as well as that of their children."
—Ruthann Rudel, Research Director at Silent Spring Institute and Research Associate at Brown University

“Compellingly readable…a stirring call to action about the dangers posed by declining fertility, including the risks to our health, our economy, and even the future of the human race.”
—Jeremy Grantham, cofounder of investment management firm GMO and the Grantham Foundation for Protection of the Environment

“Scholarly, careful, and thoroughly provocative. Swan and Colino explore every aspect of human fertility, sexuality, and reproduction—as well as the fate of other species—with wisdom, compassion, and insight. An important and recommended read.”
—David L. Katz, MD, MPH, President of True Health Initiative and Past President of American College of Lifestyle Medicine

Count Down is that rarest of books: a compelling and engaging overview that not only rings the alarm bell, but provides ideas for putting out the fire. Read this book if you want to protect your family’s health.”
—Rick Smith, coauthor, Slow Death by Rubber Duck

“Swan solves one of the great mysteries of the moment: why sperm counts and fertility rates are dropping. She zeroes in on chemicals as a chief culprit, but, even more admirably, maps out the entire threat landscape. This book shines an important light on what we need to do to bring back healthy reproduction.”
—David Michaels, former Assistant Secretary of Labor for OSHA and author of The Triumph of Doubt: Dark Money and the Science of Deception

“Unique, exhaustively researched, well-reasoned…Count Down makes a compelling case for changing what we think we know about the future of the human species.”
—Darrell Bricker, coauthor of Empty Planet: The Shock of Global Population Decline

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