Hagai Levine doesn't scare easily. The Hebrew University public health researcher is the former chief epidemiologist for the Israel Defense Forces, which means he's acquainted with danger and risk in a way most of his academic counterparts aren't. So when he raises doubts about the future of the human race, it's worth listening. Together with Shanna Swan, a professor of environmental medicine and public health at the Icahn School of Medicine at Mount Sinai, Levine authored a major new analysis that tracked male sperm levels over the past few decades, and what he found frightened him. "Reproduction may be the most important function of any species," says Levine. "Something is very wrong with men."
That's something you may not be used to hearing. It may take a man and a woman—or at least a sperm and an egg—to form new life, but it is women who bear the medical and psychological burden of trying to get—and stay—pregnant. It is women whose lifestyle choices are endlessly dissected for their supposed impact on fertility, and women who hear the ominous tick of the biological clock. Women are bombarded with countless fertility diets, special fertility-boosting yoga practices and all the fertility apps they can fit on their phone. They are the targets of a fertility industry expected to be valued at more than $21 billion globally by 2020. Even the Centers for Disease Control and Prevention fixates on women, tracking infertility in the U.S. by tallying the number of supposedly infertile women. "It is as if the entire medical realm is shaped to cater to women's infertility and women's bodies," says Liberty Barnes, a sociologist and the author of Conceiving Masculinity: Male Infertility, Medicine, and Identity. "For men, there's just nothing there."
That absence might be understandable if women were solely responsible for the success or failure of a pregnancy. But they're not. According to the American Society for Reproductive Medicine, the male partner is either the sole or contributing cause in about 40 percent of cases of infertility. Past infections, medical conditions, hormonal imbalances and more can all cause what is known as male factor infertility. Men even have their own version of a biological clock. Beginning around their mid-30s, male fertility gradually degrades, and while most men produce sperm to their dying day, those past 40 who help conceive have a greater risk of passing on genetic abnormalities to their children, including autism. "Men are a huge part of this problem," says Barbara Collura, the president and CEO of Resolve: the National Infertility Association.
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Startling new evidence suggests male infertility may be much worse than it appears. According to Levine and Swan's work, sperm levels—the most important measurement of male fertility—are declining throughout much of the world, including the U.S. The report, published in late July, reviewed thousands of studies and concluded that sperm concentration had fallen by 59.3 percent among men in Western countries between 1973 and 2011. Four decades ago, the average Western man had a sperm concentration of 99 million per milliliter. By 2011, that had fallen to 47.1 million. The plummet is alarming because sperm concentrations below 40 million per milliliter are considered below normal and can impair fertility. (The researchers found no significant declines for non-Western men, in part because of a lack of quality data, though other studies have found major drops in countries like China and Japan.) And the decline has grown steeper in recent years, which means that the crisis is deepening. "This is pretty scary," says Swan, who has long studied reproductive health. "I think we should be very concerned about this trend."
Although there have reports of declining sperm counts before, they were easy to ignore. Research on sperm levels has been spotty, using different methodologies and drawing from varying groups, making it difficult to know that the declines some scientists observed were real, and not a function of miscounting. Skeptics of the latest conclusions countered that the new report was a study of many studies—it could only be as good as the work from which it drew. And even if the conclusions of the meta-analysis are accurate, the average sperm count still leaves most men on the normal side of fertile. Just barely.
Yet fertility rates—the number of live births per woman—have drastically declined in the same countries with falling sperm counts. That includes the U.S., where fertility rates hit a record low this year, and where women are no longer bearing enough children to replace the existing population. Women need to average roughly 2.1 children—enough to replace themselves and their partner, with a spare bit to offset kids who don't survive to reproductive age—to keep a country's population stable through birth alone. The U.S. is at 1.8 and dependent on continued immigration to keep the population growing. Sociological and economic factors play a role in the changing size of the American family. Fertility rates were above the replacement level until the 2007 recession, then they plunged. And despite a years-long economic recovery and low unemployment, they're still falling. Pair that with studies showing that nearly one in six couples in the U.S. trying to get pregnant can't do so over the course of a year of unprotected sex—the medical definition of infertility—and it's clear that something beyond economic insecurity is preventing Americans from having as many babies as they want. "When I see birth rates going down, I worry as a fertility doctor that men's sperm counts are declining," says Harry Fisch, a urologist at Weill Cornell Medicine in New York.
This would seem to be the moment for the medical world to throw everything it can at understanding what is happening to male fertility. Yet researchers on male reproduction are forced to rely on less-than-perfect data because the kind of comprehensive, longitudinal studies that might conclusively tell us what is happening to sperm counts have never been done. The irony is that the medical establishment has been accused—with reason—of ignoring the particular needs of women over the years, yet in reproduction it is men whose problems are poorly studied and often misunderstood. Some experts even wonder whether an unconscious desire to ignore threats to male fertility may be tied up in fears over the future of masculinity itself. "Here is direct evidence that that function of reproduction is failing," says Michael Eisenberg, a urologist and an associate professor at Stanford University, referring to the latest sperm-level research. "We should try to figure out why that is."
What we do know about declining sperm counts tells us a great deal about not only reproduction but also the overall health of men—and what it tells us isn't good. Young men may think themselves invincible, but the male reproductive system is a surprisingly temperamental machine. Obesity, inactivity, smoking—your basic poor modern lifestyle choices—can dramatically reduce sperm counts, as can exposure to some environmental toxins. Low sperm counts may presage a premature death, even among men in the prime of their lives who might seem otherwise healthy. "Sperm count decline is the canary in the coal mine," says Levine. "There is something very wrong in the environment." Which means there may be something very wrong with men.