The internet was abuzz about sperm last week, thanks to a new study that revealed an alarming drop in sperm counts for men in Western countries. Does this mean men are becoming infertile? Will we have problems having babies? It’s not time to panic — at least, not yet.
To be clear: the findings are worrisome. The researchers dug through thousands of studies from around the world, and found that for men living in Western countries sperm count has plummeted by between 50 and 60 percent since 1973. (Sperm count is the amount of sperm in the semen released in one ejaculation.) But that drop still leaves the average sperm count within a healthy, fertile range.
“Does this mean we’re heading into a Children of Men type of situation?” says John Amory, a professor and fertility expert at the University of Washington, who was not involved in the study. “I doubt that very much, I’m glad to say.” Still, infertility can have a serious, and negative impact on people’s lives, and it’s important to nail down whether it is indeed on the rise, and why. “It should be seen as a wake-up call,” agrees Michael Eisenberg, a urologist at Stanford University, “but not necessarily the end of days.”
Scientists have been debating whether sperm count has been going down for about 25 years, ever since researchers in Denmark published a study in 1992 showing a 50 percent drop in sperm count between 1940 and 1990. Since the odds of fathering a child tend to increase with sperm quantity (although quality matters, too), a fall in sperm count could mean an overall drop in male fertility.
Some believed this frightening claim, suspecting that the ongoing decline might be triggered by smoking and exposures to pesticides or components of plastics leaching into our food and disrupting hormones. But others disputed it, believing that sperm’s disappearing act was a result of the different way scientists have counted and studied semen over the years.
Researchers led by Shanna Swan, a reproductive scientist at the Icahn School of Medicine at Mount Sinai, wanted to put the debate to rest. They screened more than 2,500 studies that reported sperm counts since 1973, filtering out papers that were too small, used dubious methods, or that specifically looked at infertile men. Instead, they picked studies that counted sperm the same way in semen collected from men who either didn’t know if they were fertile, or who knew for certain that they were.
Then, they compared the results for men of the same age, from 1973 to 2011: the results show that for men living in Western countries, sperm concentrations and absolute sperm number have dropped between 52 and 59 percent. (Sperm concentration is the amount of sperm in a milliliter of semen; absolute sperm number is the amount in the total volume of a single ejaculation.) The findings were published in the journal Human Reproduction Update.
Here’s why you shouldn’t freak out: sperm concentration went from about 99 million sperm per milliliter of splooge in 1970 to 47 million sperm per milliliter in 2010. “They’re well within the fertile range,” Amory says. “They’re falling from fertile to fertile.” For reference, men can have a tougher time conceiving if sperm count falls below 40 million sperm per milliliter. The World Health Organization considers sperm concentrations less than 15 million sperm per milliliter of semen to be abnormally low.
But the study also didn’t find any evidence that this decline was slowing down or stopping. That means that if sperm count continues to plummet, then we could see more men having problems conceiving. “It’s concerning — it’s important we figure out what’s going on,” Swan says.
That’s because sperm counts are important for more than just fertility: sperm — as the authors of the study put it — are the tadpole-shaped “canaries in the coal mine” when it comes to health. Making sperm takes a complex series of events: it starts with producing hormones in the brain, which stimulates sperm production in the testicles. That sperm is then shuttled through a network of pipes, mixed with other ingredients, and shot out into the world. It’s like a long chain of dominos, and if any have been knocked askew by, say, injury, infection, or any number of other unknown cases, they won’t all fall neatly into place. So, if sperm counts are dropping, it could be a sign that something is damaging men’s overall wellbeing. In fact, lower sperm counts have been linked to poorer health.
The current study couldn’t get at exact causes. But it’s thought that if pregnant women are exposed to cigarette smoke, certain pesticides, and ingredients in plastics that can disrupt hormones, it may have long-term effects on a male fetus’s future fertility. For adult men, obesity and smoking may also lower sperm counts — although we don’t know for certain.
This study is a start toward settling the debate, but there are still some caveats: men can produce different amounts of sperm even at different points throughout the day, for instance. And there’s more to fertility than just number of sperm — sperm wiggliness and shape, for example, are important, too.
To figure exactly what’s going on, we need more research. If the Centers for Disease Control and Prevention were to actively collect data on semen over time, that could go a long way toward confirming a decline and helping researchers spot possible causes, Eisenberg says. “It’s concerning as a species, and it needs to be tracked more rigorously,” he says. “If it’s confirmed, we should be very concerned — and find a way to stop it.”