Sperm counts worldwide are plummeting faster than we thought

Five years ago, a study describing a precipitous decline in sperm counts sparked extreme concerns that humanity was on the path to extinction. A new study has shown that sperm counts are falling faster than expected, raising concerns about a global fertility crisis.

The initial study, published in July 2017, revealed that sperm counts–the number of sperm in a single ejaculate–plummeted by more than 50 percent among men in North America, Europe, Australia, and New Zealand between 1973 and 2011. Since then, a team led by the same researchers has explored what has happened in the last 10 years. In a new meta-analysis, which appears today in the journal Human Reproduction Update, researchers analyzed studies of semen samples published between 2014 and 2019 and added this to their previous data. The newer studies have a more global perspective and involved semen samples from 14,233 men, including some from South and Central America, Africa, and Asia. The upshot: Not only has the decline in total sperm counts continued–reaching a drop of 62 percent–but the decline per year has doubled since 2000.

The 2017 report also revealed that sperm concentration (the number of sperm per milliliter of semen) dropped by an average of 1.6 percent per year, totaling more than a 52 percent among men in these regions over the previous four decades. The decline is not tapering down–it’s steeped and significant,” Shanna Swan, co-author of the study and a reproductive and environmental epidemiologist at Mount Sinai in New York City’s Icahn School for Medicine, said. “Overall the drop is similar in magnitude but when we look at recent years, we see that it’s speeding up.”

Study lead author Hagai Levine, a medical epidemiologist at Hebrew University of Jerusalem’s Hadassah Braun School of Public Health, calls the results “worrisome as we were hoping that at some point the decline would be leveling off. The opposite may be true, and we may cross a tipping point when most men will be sub-fertile or when the causes of this decline will also manifest by other adverse health trends.”

Rising infertility

Contrary to common perception, infertility impacts men and women equally, says Amy E.T. Sparks is a reproductive physiologist and director of IVF and Andrology Laboratories at University of Iowa Center for Advanced Reproductive Health. “I believe that infertility is perceived as primarily a problem of women.” The scientific community believes that about one-third (or more) of cases of infertility are due to male and female fertility problems. The remaining cases are caused by a combination of male factors and female factors.

But new data suggests that there has been a significant increase in the number of men with low fertility. This can lead to lower fertility rates for their partners, according to David M. Kristensen (a molecular toxicologist at Roskilde University in Denmark and Copenhagen University Hospital in Denmark). He was not involved in this study. “This is of concern for not only the families that are affected but also for societies in general, as many countries such as Italy and Japan are already suffering from shrinking populations.”

Beyond reproductive matters, there’s also a concern that reduced sperm counts are associated with a variety of health problems in men. “There is a link between semen quality, overall health–studies indicate that impaired semen quality is associated a higher risk of testicular carcinoma, cardiovascular disease and [premature] death,” says Michael Eisenberg, director of male reproduction medicine and surgery at Stanford University School of Medicine. He was not involved with either meta-analysis. Kristensen says that one can look at sperm count declines as a biomarker of male health in general.

In fact, a study in a 2018 issue of the journal Andrology found a higher risk of hospitalization among men who had lower sperm concentrations. Those with sperm concentrations below 15 million/mL–considered low–had a 53 percent greater risk of being hospitalized for any reason over the course of 36 years than those with more robust sperm concentrations between 51 and 100 million/mL. Even after controlling for body weight, smoking, etc., the effect remained.

Complicating factors

It’s important to note that the decline in sperm counts isn’t happening in a vacuum. Low sperm count often goes hand in hand with low testosterone levels and changes in male genital development while in the womb, says Swan, author of the book Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race.

In a man, the production of sperm requires a certain level of testosterone as well as the testes’ ability to regulate the temperature of the tissue in which sperm are made, Sparks explains. “Levels of testosterone have been reported to be declining during the same period of time that the sperm production rates were measured in this meta-analysis.”

It’s also important to recognize that it’s not just a matter of what a man is exposed during his lifetime that can affect his sperm quality. The sperm quality of male offspring can be affected by what an expectant mother is exposed during pregnancy. Swan explains that certain environmental chemicals can cause permanent changes in the reproductive development of male babies. She says that any disruption in reproductive development in utero is irreversible.

However, damage to sperm can be reversed by stopping exposure to harmful chemicals. It takes about 75 days for sperm to mature, says Swan, which means that men essentially have regular opportunities for a do-over for their sperm quality every two and a half months.

What’s driving the decline?

Neither the 2017 nor the 2022 meta-analyses examined what is causing the drop in sperm count, but other research suggests environmental and lifestyle factors may be to blame. These include smoking, obesity, and exposure to endocrine disrupting chemicals (which mimic or interfere in the body’s hormones). For example, a study in a 2022 issue of the journal Toxicology found that occupational exposure to pesticides was associated with sperm found in lower concentrations, sperm that were poor swimmers, and sperm with more DNA damage. And a study in a 2019 issue of the journal Human Reproduction found that men who are overweight tend to have reduced sperm concentration, lower total sperm count, and fewer motile sperm. According to Swan, the fact that sperm counts are declining in South and Central America, Africa and Asia suggests that lifestyle and environmental factors that could be responsible are widespread.

No one knows the exact cause of the rapid decline in sperm count according to the new meta-analysis. Levine suggests that it could be due to “mixture effect” with chemicals. This means that when different chemicals are combined in the environment, they can have a greater, more harmful impact by magnifying their negative effects. Or, he says, the decline may result from “cumulative exposure over time.”

Given that the latest meta-analysis included data from 50 years, Swan suspects the acceleration stems from the cumulative impact of environmental chemicals over generations. Remember that while in the womb, the male fetus is exposed the same chemicals and lifestyle factors (such as poor diet, smoking, obesity) that his mother is exposed during pregnancy. These exposures can be passed from one generation to another. The epigenetic effects may also be transmitted from the father to the next. Levine suggests that it could be due to factors in the father’s sperm, which can disrupt the reproductive development in the womb of male fetuses.

The effects of these environmental chemicals and other harmful lifestyle factors may become more severe over time.

A wake-up call

More research needs to be done to determine what is tanking sperm counts. Men and women can take steps to protect their reproductive health by eating healthy, exercising regularly, keeping a healthy weight, and quitting.

Swan recommends that you be a smart consumer to reduce your exposure to hormone-disrupting chemicals. These chemicals include phthalates (in plastics as well as personal-care products like nail polishes, shampoos, hair sprays, and other chemicals), bisphenol A (in hardplastics, adhesives and the linings of some food cans), flame-retardants (in furniture, carpets), perfluoroalkyl compounds (in nonstick cookware, stain-resistant carpets), pesticides (in lawn-care products and plant-based foods).

Ultimately, Levine and Swan say that local and global actions are needed to reduce or get rid of these chemicals in our environments. Levine states that we should find ways to prevent further declines and even reverse the trends. “We must avoid being complacent about it and fool ourselves that assisted reproduction is the solution.”

EDITOR’S NOTE: Stacey Colino is the co-author of Count Down but had no involvement with the research discussed in this article.