A new book makes the case that sperm counts have been falling for decades — and a major reason is chemicals in the environment that disrupt the body's hormonal system.
Why it matters: The ability to reproduce is fundamental to the viable future of any living thing. If certain chemicals are damaging our fertility over the long term, human beings could end up as an endangered species.
What's happening: In 2017, Mt. Sinai Medical School epidemiologist Shanna Swan co-authored a sweeping meta-analysis that came to a startling conclusion: Total sperm count in the Western world had fallen 59% between 1973 and 2011.
- Together with falling testosterone levels and growing rates of testicular cancer and erectile dysfunction, that translated into a 1% increase per year of adverse reproductive changes for men, according to Swan.
Driving the news: Now Swan has written up her conclusions in a new book with a foreboding title: "Count Down: How Our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race."
- "If you look at the curve on sperm count and project it forward — which is always risky — it reaches zero in 2045," says Swan, meaning the median man would have essentially no viable sperm. "That's a little concerning, to say the least."
By the numbers: The global fertility rate — the number of births per woman — has fallen from 5.06 in 1964 to 2.4 in 2018.
Yes, but: There are numerous factors connected to falling fertility rates that appear largely unconnected to sperm counts.
Still, there's a gap around the world between the number of children people say they want and the number they actually have, which indicates at least some of the decline in the fertility rate isn't wholly voluntary.
The big picture: Swan and many of her colleagues point the finger at chemicals in the environment that disrupt hormones or endocrines.
- These include phthalates and bisphenol-A, known as "everywhere chemicals" because of their ubiquity in things like plastics, pesticides, cosmetics and even ATM receipts.
The other side: As Swan herself notes, there are other factors at play impairing male and female fertility beyond environmental chemicals, including smoking tobacco and marijuana and rising levels of obesity.
- Trade groups — and some scientists — have pushed back against studies that connect endocrine-disrupting chemicals to fertility problems.
Our thought bubble: A growing number of scientific institutions have raised the alarm about endocrine-disrupting chemicals, and Swan puts together a strong case that impaired fertility is real and its causes go beyond separate health problems or lifestyle choices.
The bottom line: "The current state of reproductive affairs can't continue much longer without threatening human survival," Swan writes.