A Threat to Male Fertility

Deborah Blum

March 21, 2014

New York Times Blog

To study the impact of everyday chemicals on fertility, federal researchers recently spent four years tracking 501 couples as they tried to have children. One of the findings stood out: while both men and women were exposed to known toxic chemicals, men seemed much more likely to suffer fertility problems as a result.

The gender gap was particularly wide when it came to phthalates, those ubiquitous compounds used to make plastics more flexible and cosmetic lotions slide on more smoothly. Women who wore cosmetics often had higher levels of phthalates in their bodies, as measured by urinalysis. But only in their male partners were phthalate levels correlated with infertility.

“It’s the males in the study that are driving the effect,” said Germaine Buck Louis, an epidemiologist at the National Institute of Child Health and Human Development and lead author of the report, published in February in Fertility and Sterility. “They’re the signal.”

Poison Pen
POISON PEN

Deborah Blum writes about chemicals and the environment.

Phthalates belong to a group of industrial compounds known as endocrine disruptors because they interfere with the endocrine system, which governs the production and distribution of hormones in the body. The chemicals have been implicated in a range of health problems, including birth defects, cancers and diabetes.

But it is their effect on the human reproductive system that hasmost worried researchers. A growing body of work over the last two decades suggests that phthalates can rewire the male reproductive system, interfering with the operation of androgenic hormones, such as testosterone, that play key roles in male development. That mechanism, some experts believe, explains findings that link phthalate exposure to changes in everything from testicular development to sperm quality.

“I wasn’t surprised at all by this finding,” Andrea Gore, a professor of pharmacology and toxicology at the University of Texas, and editor in chief of the journal Endocrinology, said of the new report. “We see the cell studies, the animal studies and now the human epidemiology work, and they are all showing us a similar picture.”

The focus on male fertility dates back to the early 1990s, when researchers in the United States and Europe published a paper suggesting chemical exposures could be linked to a steady decline in semen quality. One of the authors, Niels Skakkebaek, a reproduction researcher at the University of Copenhagen, has since suggested that an increase in malformations in male reproductive systems, which he calls “testicular dysgenesis syndrome,” may belinked to environmental exposure to compounds including endocrine disruptors like phthalates.

More recent studies in the United States have also suggested links between phthalate exposure and apparent sperm damage in men. The findings are supported by a host of animal studies, particularly in rats, which have shown that the compounds can interfere with masculinization of young animals and result in odd physical changes to male reproductive tracts.

“They interfere with how testosterone is made,” explained Heather Patisaul, a biology professor at North Carolina State University who is studying the effect of endocrine-disrupting compounds during puberty. “Anything you can think of that’s testosterone-dependent is likely to be affected.”

Women also have androgenic hormones, but to a lesser degree, and according to some theories this accounts for the smaller but still observable effects of phthalates on female fertility. (Testosterone, for instance, is part of the cascade of hormones that leads to egg.

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