In the science fiction film, Children of Men, humans in the year 2027 face extinction due to decades of infertility. This premise doesn’t seem all that far-fetched when you consider studies in the U.S., Japan, and Europe over the past two decades that point to declining sperm counts. A 2013 study, for instance, that followed 26,000 French men for 17 years reported a 32% drop in sperm counts. And a study of 5000 Danish men with a median age of 19 found 40% had sperm counts corresponding to infertility or decreased fertility.
So what’s going on here? One line of evidence blames exposure to chemicals that leach into our food and water supply. A possible culprit is the much-despised Bisphenol-A, or BPA, a man-made chemical found in plastic bottles, the inner linings of canned food and even receipt paper used at your local grocery store. BPA is known as a hormone disruptor because it interferes with normal hormone activity in the body by mimicking the female hormone estrogen. Lab animals exposed to low levels of BPA have shown increased incidence of certain cancers, neurological problems, diabetes, obesity, female reproduction problems and, yes, decreased sperm counts.
Data published last week in PLOS Genetics appears to have pinpointed the link between BPA and decreased sperm counts: stem cells. Specifically the so-called spermatogonial stem cells that give rise to sperm. In the Washington State University study, the research team gave newborn male mice daily oral doses of BPA for about two weeks. The chemical exposure negatively affected this spermatogonial stem cell population by disrupting the processing of the cells’ DNA and, in turn, the development of fully mature sperm. The team got similar results replacing BPA with synthetic estrogen found in birth control pills. This form of estrogen is also known to contaminate our water supply even after sewage treatment.
A surprising and even scary twist to these results is that the brief exposure of BPA or estrogen in the newborn male mice permanently changed their stem cells. The team confirmed this observation by transplanting the spermatogonial stem cells from BPA-exposed mice into the testes of mice that never received BPA. In this case, these mice still exhibited reduced sperm production. As senior author Nancy Hunt points out in an interview with Scientific American, the exposure to these chemicals:
“is not simply affecting sperm being produced now, but impacting the stem cell population, and that will affect sperm produced throughout the lifetime.”
It’s remains debatable whether the detectable BPA or estrogen levels in our food and water supply is high enough to actually cause health problems in humans. In 2013 the Food and Drug Administration (FDA) downplayed possible worries on its website:
“Is BPA safe? Yes. Based on FDA’s ongoing safety review of scientific evidence, the available information continues to support the safety of BPA for the currently approved uses in food containers and packaging.”
Still, this recent study and others like it certainly warrant further investigation. University of Missouri scientist Frederick vom Saal, who was not part of the study, put it this way in his interview with Scientific American:
“It’s important in future studies to see if the stem cell changes from exposure are passed to future generations… Since most people are consistently exposed to BPA and other estrogenic compounds, each generation could have it a bit worse.”