Many men today have just half the number of sperm their grandfathers had. The shocking discovery was published in 2017 by Shanna Swan, PhD, an environmental and reproductive epidemiologist at the Icahn School of Medicine at Mount Sinai in New York.
After analyzing 185 studies involving nearly 45,000 healthy men, Swan and her team found that over the past four decades, sperm counts among men in Western countries had dropped by more than 50%.
Why the huge decline? Swan says many factors are at play — alcohol use, smoking, body weight, and a lack of exercise are a few. But she has zeroed in on another, more insidious cause: exposure to common chemicals that interfere with the body’s production of hormones.
Swan has been studying these so-called endocrine disruptors for the past 30 years. And it turns out men’s sperm isn’t the only thing they affect: They may be changing human sexual development and reproduction in broader ways, too. In girls, exposure to such chemicals has been linked to earlier onset of puberty. Women, meanwhile, are experiencing a decline in egg quality and more miscarriages.
In a new 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, Swan outlines the hidden damage these chemicals are having on our fertility and why we must act now to prevent them from causing further damage.
In the book, she makes a provocative claim: Humans may not have the ability to reproduce naturally for much longer. She estimates that by 2050, a large portion of the global population will need assisted reproductive technology to procreate. I talked to Swan to learn more about these chemical exposures and what can be done to avert an infertile future.