I can’t remember when I learned that women’s fertility starts to wane in our 30s; it feels like I was born knowing that my eggs had a sell-by date. Men, conversely, are rarely encouraged to think about their ability to have children.
The discussion around healthy sperm seems confined to cloistered and strange subcultures, like natalist group chats and tech bro sperm races. The latter is a real thing in Los Angeles, where men raced their sperm against each other.
Male fertility deserves broader consideration outside these isolated spaces. Mounting evidence suggests that exposure to so-called endocrine-disrupting chemicals present in many products, from food and beverage containers to furniture and agricultural pesticides, may affect male potency from the very beginning of life.
The idea that sperm counts and quality have declined over the past 50 years, possibly because of environmental toxins, is not new, and there’s great disagreement about it. But even if the science is unsettled, the warning signs are worth taking seriously.
Research suggests that if a woman is overexposed to endocrine-disrupting chemicals during early pregnancy, there are potential reproductive and hormonal risks for a male fetus. Boys may have a shorter taint, the colloquial term for the distance between their anus and their genitals, which is associated with lower sperm count and movement. And there are problems beyond the taint, including lower testosterone levels, an increased risk of undescended testicles or a type of malformed penis, according to the environmental and reproductive epidemiologist Shanna Swan in her 2021 book, “Count Down,” which details the pernicious ways these chemicals affect both male and female fertility.
A few months after birth, male babies enter a “mini-puberty,” when they experience a brief surge of testosterone that helps prepare the body for the full hormonal changes of actual puberty, said Linda Kahn, an assistant professor of pediatrics at N.Y.U. Grossman School of Medicine. If a male infant is exposed to endocrine-disrupting chemicals during this period, it may impair what’s known as Sertoli cells, which are essential to the creation of healthy sperm. There’s also evidence that exposure to phthalates, a plastic softening agent used in all kinds of consumer products, and pesticides used in agricultural production can affect sperm count and quality in adolescent boys and in men.
Endocrine disrupters are basically everywhere in our postindustrial world. And there’s a great deal of scientific disagreement around what — if any — levels of exposure are safe for humans. Because we’re all exposed to multiple kinds of these chemicals, and because there’s so much variation in that exposure among people, it’s difficult to say, in any definitive way, what levels of particular chemicals are dangerous, and for whom. Scientists can’t do the gold standard, randomized controlled studies on these chemicals, because it would be unethical to expose people to substances researchers already know may be damaging.
A 2017 meta-analysis on semen that Dr. Swan co-wrote made headlines because it showed that sperm concentration and count among men in Western countries had declined precipitously from 1973 to 2011. That study received a lot of media attention, and so did studies that pushed back against its findings.
There are challenges to gathering historical sperm counts and making comparisons over time. Sperm counts are a flawed measure of fertility, critics argued, and, even after decades of purported decline, average sperm counts among Western men were still within the normal range, as defined by the World Health Organization, according to a 2021 paper that proposed a different framework from Dr. Swan’s approach.
But Dr. Swan has come out with more evidence since then. She and her fellow researchers published another meta-analysis in 2023 that included more robust data from non-Western countries up to 2018. They discovered that sperm counts had declined everywhere. The mean sperm count among men worldwide had declined by over 50 percent from the early 1970s, and the rate of decline increased after 2000.
There are factors outside of chemical exposure that can impact male fertility. Lifestyle behaviors like smoking, drug and alcohol use, poor diet and lack of exercise affect male fertility as well. In terms of the overall decline in the birthrate throughout the world, personal choice and readily available birth control are also major factors.
But Dr. Swan thinks we may be underestimating how much the deterioration of sperm is influencing overall fertility. “The animal evidence is really important,” she told me. Studies have shown that endocrine-disrupting chemicals also affect the fertility of many different kinds of male wildlife, and it’s not as if fish are deciding to put off childbearing until they’re more financially stable.
When it comes to infertility, there’s still a huge bias against women. “Women are blamed for anything going wrong,” said Dr. Swan. We should change that. I have been convinced by the data that men should start getting fertility assessments as a basic standard of care, just like women have annual visits at the gynecologist.
In the journal Biology of Reproduction, two researchers, Vardit Ravitsky and Sarah Kimmins, made the case in 2019 for “incorporating sperm screens into primary care checkups.” They also went a step further. Because “robust evidence shows plummeting sperm counts and declining sperm quality in men after the age of 40,” and many male-dominated professions like firefighting involve exposure to chemicals that are hazardous to fertility, they argued that young men should start thinking about freezing their sperm, just as women are thinking about egg freezing. There’s a growing market for it, too.
At the very least, men should be aware that half of all infertility cases are caused by male infertility. Not just because it may make them start embracing healthier lifestyles if they hope to have children some day, but also because if they are intimately aware of their own deficient sperm, they might be more motivated to push for the policy changes that would really help fix male infertility on a larger scale.
Because the truth is that while lifestyle changes can make a difference, there is only so much an individual can do (though everybody should definitely stop microwaving things in plastic). “It’s sort of nibbling around the edges,” said Dr. Kahn. Her biggest policy recommendation is that the United States adopt the European method of evaluating and regulating chemicals, which is based on the precautionary principle. Basically, a substance has to be proved safe before it is allowed to be used commercially.
While the health and human services secretary, Robert F. Kennedy Jr., has committed to revising a U.S. regulation loophole so that corporations must notify the Food and Drug Administration when introducing a new ingredient to the food market, he has not agreed to completely rearrange the way chemicals are evaluated so that the rules more closely resemble the European Union’s regulation.
Set against the backdrop of an Environmental Protection Agency led by Lee Zeldin, who is gleefully destroying regulations for clean air and water, it’s difficult to imagine that the overall environment is going to improve for male fertility. As Dr. Kahn explained to me, when government researchers are testing a new chemical for safety, they don’t always test for endocrine disruption; they test for things like birth defects and cancer. “That’s a fight that we’re fighting,” she told me.
I’m glad she’s raising concerns about the ubiquity of endocrine disrupting chemicals. I don’t want to have to spend my time thinking about how many microplastics I’m huffing every time I eat out of a plastic container, or worry about the future fertility of my children, and their children. I want the people in charge of chemical regulation across the world to actually care about this. If hobbled sperm is what’s going to change hearts and minds, then let’s strike up the band and play “Every Sperm Is Sacred” at national sporting events. I’m ready.
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Jessica Grose is an Opinion writer for The Times, covering family, religion, education, culture and the way we live now.
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