Sperm Count Zero

Sperm Count Zero, by Daniel Halpern.

Last summer a group of researchers from Hebrew University and Mount Sinai medical school published a study showing that sperm counts in the U.S., Europe, Australia, and New Zealand have fallen by more than 50 percent over the past four decades. (They judged data from the rest of the world to be insufficient to draw conclusions from, but there are studies suggesting that the trend could be worldwide.) That is to say: We are producing half the sperm our grandfathers did. We are half as fertile.

The Hebrew University/Mount Sinai paper was a meta-analysis by a team of epidemiologists, clinicians, and researchers that culled data from 185 studies, which examined semen from almost 43,000 men. It showed that the human race is apparently on a trend line toward becoming unable to reproduce itself. Sperm counts went from 99 million sperm per milliliter of semen in 1973 to 47 million per milliliter in 2011, and the decline has been accelerating. Would 40 more years—or fewer—bring us all the way to zero? …

If we are half as fertile as the generation before us, why haven’t we noticed? One answer is that there is a lot of redundancy built into reproduction: You don’t need 200 million sperm to fertilize an egg, but that’s how many the average man might devote to the job. Most men can still conceive a child naturally with a depressed sperm count, and those who can’t have a booming fertility-treatment industry ready to help them. And though lower sperm counts probably have led to a small decrease in the number of children being conceived, that decline has been masked by sociological changes driving birth rates down even faster: People in the developed world are choosing to have fewer children, and they are having them later. …

Testosterone levels have also dropped precipitously, with effects beginning in utero and extending into adulthood. …

So what was causing this disruption? To say there is only a single answer might be an overstatement — stress, smoking, and obesity, for example, all depress sperm counts — but there are fewer and fewer critics of the following theory: The industrial revolution happened. And the oil industry happened. And 20th-century chemistry happened. In short, humans started ingesting a whole host of compounds that affected our hormones — including, most crucially, estrogen and testosterone.

Correlation doesn’t necessarily mean causation, but it’s pretty striking

Anna-Maria Andersson [is] a biologist whose research has focused on declining testosterone levels. “There has been a chemical revolution going on starting from the beginning of the 19th century, maybe even a bit before,” she told me, “and upwards and exploding after the Second World War, when hundreds of new chemicals came onto the market within a very short time frame.” Suddenly a vast array of chemicals were entering our bloodstream, ones that no human body had ever had to deal with. …

What’s more, there is evidence that the effect of these endocrine disruptors increases over generations, due to something called epigenetic inheritance. Normally, acquired traits—like, say, a sperm count lowered by obesity—aren’t passed down from father to son. But some chemicals, including phthalates and BPA, can change the way genes are expressed without altering the underlying genetic code, and that change is inheritable. Your father passes along his low sperm count to you, and your sperm count goes even lower after you’re exposed to endocrine disruptors. That’s part of the reason there’s been no leveling off even after 40 years of declining sperm counts — the baseline keeps dropping. …

Assuming that we’re unable to wean ourselves off plastics and other marvels of modern science, we may be stuck innovating our way out of this mess. How long we’re able to outrun the drop in sperm count may depend, finally, on how good we get at IVF and other fertility treatments.