Chemicals that pervade our modern world — plastics, pesticides, stain repellents, components of personal hygiene products — are contributing to a decades-long decline in fertility and could pose health risks even into future generations, according to an explosive new book by Shanna Swan, PhD, an environmental and reproductive epidemiologist at the Icahn School of Medicine at Mount Sinai, New York.
Swan laid out the case that endocrine-disrupting chemicals (EDCs) such as phthalates and bisphenol A (BPA) threaten human existence, a conclusion that stems in part from her 2017 meta-analysis that showed a 52% drop in sperm counts from 1973 to 2011 in men in North America, Europe, and Australia.
"This alarming rate of decline could mean the human race will be unable to reproduce itself if the trend continues," Swan said in her 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," (New York: Scribner, 2021) coauthored with health journalist Stacey Colino.
Her premise that EDCs pose a risk to both male and female fertility is underscored by new research. A March 2021 article in Human Reproduction links prenatal chemical exposures to lowered fertility in a study of 1,045 Swiss military conscripts.
The Swiss men, aged 18-22 years, were significantly more likely to have low semen volume and low total sperm count if their mothers reported that they had occupational exposures to four or more endocrine-disrupting chemicals while they were pregnant. These EDCs, which mimic natural hormones, included pesticides, heavy metals, phthalates, alkylphenolic compounds, and solvents that can be found in agricultural work or hair and beauty salons.
These chemicals are not so-called "forever chemicals" that persist in the human body. But the Swiss study still showed an association between exposure during pregnancy and the future fertility of the male children. "Those apparently small exposures that pass quickly can affect development," said Swan, who was not affiliated with the research. "It takes very little in terms of time and amount of chemicals to alter fetal development."
Health Risks Beyond Reproduction
While Count Down is placing a new spotlight on chemical hazards, some major medical organizations have already taken positions on the risks. "Reducing exposure to toxic environmental agents is a critical area of intervention for ob.gyns.," the American College of Obstetricians and Gynecologists said in an environmental policy priority. "The Endocrine Society is concerned that human health is at risk because the current extensive scientific knowledge on EDCs and their health effects is not effectively translated to regulatory policies that fully protect populations from EDC exposures."
But for the medical community, addressing the impact of EDCs goes beyond advocacy for regulatory and legislative changes, Swan said in an interview. Physicians should talk to patients about the importance of reducing their chemical exposure to safeguard their overall health.
"Reproductive health and particularly sperm count, subfertility, and infertility are predictors of lifelong health," she said. That includes associations between reproductive disorders and "the risk of heart disease, obesity, reproductive cancers and, perhaps most dramatically, with a shortened lifespan."
Some medical schools are including information on environmental health and exposure risks in the curriculum, said Tracey Woodruff, PhD, MPH, director of the program on reproductive health and the environment at the University of California, San Francisco. She urged physicians to ask patients about potential occupational exposures to hazardous chemicals and provide information about ways to reduce everyday exposures.
For example, safer options include buying organic produce, microwaving food in glass rather than plastic containers and avoiding products that contain phthalate or BPA. "If you're going to talk to people about what they eat, that's a perfect venue for talking about the environment," said Woodruff, who coedited the textbook, Environmental Impacts on Reproductive Health and Fertility (Cambridge University Press: Cambridge, England, 2010).
The UCSF program provides patient guides in English and Spanish with suggestions of ways to reduce chemical exposures at work and at home.
Limits in the Data
Michael Eisenberg, MD, a urologist and director of male reproductive medicine and surgery at Stanford (Calif.) University Medical Center, often gets questions from patients about how lifestyle and environmental exposures affect male fertility. (In her book, Swan also discusses how factors such as diet, exercise, smoking, and stress can affect male and female fertility.)
He found the evidence convincing that certain chemicals impact fertility – although, of course, it isn't ethically possible to do randomized, controlled trials in which some people are intentionally exposed to chemicals to measure the effects. Along with adopting other healthy habits, he advised patients to avoid chemical exposures.
"It's reasonable to try to eat organic and be mindful of where some of these exposures come from and try to minimize them to the extent possible," he said.
Rebecca Sokol, MD, MPH, an endocrinologist and expert in male reproductive health, demonstrated the toxic effects of lead on sperm production in studies conducted on rats. But she views low-dose chemical exposure from everyday products as just one aspect of modern reproductive risks, some of which have stronger associations. For example, testosterone therapy impairs sperm production, and finasteride (a medication for male pattern baldness) has been linked to a reversible decline in sperm count.
"When it comes to these ubiquitous chemicals like phthalate and BPA, we explain to the patient that maybe they're harmful, but we can't say for sure," because of the lack of causal data, said Sokol, professor emerita at the University of Southern California, who was on the panel that drafted the American Urological Association and American Society of Reproductive Medicine guideline on the diagnosis and treatment of male infertility.
Nonetheless, she advised patients to try to reduce exposures. "I don't see us eradicating all the chemicals that might be bad for us unless we go back to another era. But we can do the best we can to avoid what we can."
A Call to Action
Swan likened awareness of the health threat of chemical exposures to the gradual recognition of the climate crisis as a global imperative. Yet in some ways, the scientific work on chemical effects is even more daunting. The Environmental Protection Agency lists more than 86,000 chemicals on its inventory of chemical substances manufactured or imported into the United States.
Little is known about the potential effects of many chemicals that we inhale, ingest or absorb through our skin, Swan said. In her book, she noted the impact on wildlife – for example, reproductive abnormalities in frogs, alligators, and birds that were exposed to EDCs.
Yet Swan also takes solace in the lessons from the animal kingdom. Decades after the pesticide DDT, a neurotoxin and endocrine-disruptor, was banned in the United States in 1972, the bald eagle has made a comeback from near-extinction. She also pointed to a 2018 study which found that, while mice exposed to bisphenols passed on reproductive effects to offspring, when the exposures stopped, the effects disappeared after several generations.
"If we stop poisoning ourselves, we can turn this around," said Swan. "That's what I want people to know."
Count Down frames the issues in language that is much starker than typically found in academic publications. But that is what's necessary to draw attention to the effects of chemical exposures on human health and reproduction, Swan said. "I'm saying this in fairly extreme terms to alarm people, to make them realize it is a crisis and they have to act."
No disclosures were reported.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.
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Cite this: Everyday Chemicals Are Linked to Declines in Human Fertility - Medscape - Apr 09, 2021.