Why is male sperm count dropping

Last summer a group of researchers from Hebrew University and Mount Sinai medical school published a study showing that sperm counts in the U. 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. 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 to 47 million per milliliter in , and the decline has been accelerating. Would 40 more years—or fewer—bring us all the way to zero? I called Shanna H. Swan, a reproductive epidemiologist at Mount Sinai and one of the lead authors of the study, to ask if there was any good news hiding behind those brutal numbers. Were we really at risk of extinction? She failed to comfort me. When is a species in danger?

When is a species threatened? 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 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.

The problem has been debated among fertility scientists for decades now—studies suggesting that sperm counts are declining have been appearing since the '70s—but until Swan and her colleagues' meta-analysis, the results have always been judged incomplete or preliminary. Swan herself had conducted smaller studies on declining sperm counts, but in she decided it was time for a definitive answer.

The results, when they came in, were clear. Not only were sperm counts per milliliter of semen down by more than 50 percent since , but total sperm counts were down by almost 60 percent: We are producing less semen, and that semen has fewer sperm cells in it. This time around, even scientists who had been skeptical of past analyses had to admit that the study was all but unassailable.

But he couldn't argue when the team ran the numbers again and again. The downward slope was unwavering. Almost all the scientists I talked to stressed that not only were low sperm counts alarming for what they said about the reproductive future of the species—they were also a warning of a much larger set of health problems facing men.

In this view, sperm production is a canary in the coal mine of male bodies: We know, for instance, that men with poor semen quality have a higher mortality rate and are more likely to have diabetes, cancer, and cardiovascular disease than fertile men. Testosterone levels have also dropped precipitously, with effects beginning in utero and extending into adulthood.

One of the most significant markers of an organism's sex is something called anogenital distance AGD —the measurement between the anus and the genitals. Male AGD is typically twice the length of female, a much more dramatic difference than height or weight or musculature. Lower testosterone leads to a shorter AGD, and a measurement lower than the median correlates to a man being seven times as likely to be subfertile and gives him a greater likelihood of having undescended testicles, testicular tumors, and a smaller penis.

Men are producing less sperm. They're also becoming less male. I assumed that the next thing Swan was going to tell me was that these changes were all a mystery to scientists. If only we could figure out what was causing the drop in sperm counts, I imagined, we could solve all the attendant health problems at once.

But it turns out that it's not a mystery: We know what the culprit is. And it's hiding in plain sight. The sixth floor of the Rigshospitalet, a hospital and research institution in Copenhagen, houses the Department of Growth and Reproduction.

The babies are all a few floors downstairs—on six, the unit is populated not with new parents but with doctors and researchers hunched over mass spectrometers and gel imagers and the like. I was there to meet Niels E. After walking me through the lab, he showed me to his office, a cramped, closet-like space—modest for someone who is a giant in his field. When he treated a second man with the same abnormality a few years later, he began to investigate a connection. What he found was a new form of precursor cells for testicular cancer, a once rare disease whose incidence had doubled.

Moreover, these precursor cells had begun developing before the patient was even born. The science is consistent: Men today produce fewer sperm than in the past, and the sperm are less healthy. The question, then, is what could be causing this decline in fertility. Scientists have known for years that, at least in animal models , environmental toxic exposure can alter hormonal balance and throw off reproduction. As the downward trend in male fertility emerged, I and other researchers began looking more toward chemicals in the environment for answers.

These include substances like phthalates — better known as plasticizers — as well as pesticides, herbicides, heavy metals, toxic gases and other synthetic materials.

Plasticizers are found in most plastics — like water bottles and food containers — and exposure is associated with negative impacts on testosterone and semen health. Herbicides and pesticides abound in the food supply and some — specifically those with synthetic organic compounds that include phosphorus — are known to negatively affect fertility.

Air pollution surrounds cities, subjecting residents to particulate matter, sulfur dioxide, nitrogen oxide and other compounds that likely contribute to abnormal sperm quality. Radiation exposure from laptops, cellphones and modems has also been associated with declining sperm counts, impaired sperm motility and abnormal sperm shape.

Heavy metals such as cadmium, lead and arsenic are also present in food, water and cosmetics and are also known to harm sperm health. Endocrine-disrupting compounds and the infertility problems they cause are taking a significant toll on human physical and emotional health. And treating these harms is costly. A lot of chemicals are in use today, and tracking them all is incredibly difficult. More than 80, chemicals are registered in the U. Such is the gravity of the threats they pose, she argues, that humans could become an endangered species.

Between and the global fertility rate fell from 5. While contraception, cultural shifts and the cost of having children are likely to be contributing factors, Swan warns of indicators that suggest there are also biological reasons — including increasing miscarriage rates, more genital abnormalities among boys and earlier puberty for girls.

She also said factors such as tobacco smoking, marijuana and growing obesity play a role.