THURSDAY, October 28 (Health.com) — Exposure to bisphenol-A (BPA), a controversial chemical found in hard, clear plastics, is thought to increase the risk of birth defects, early puberty, obesity, brain damage, and some forms of cancer.
Add another potential problem to the list: A new study of Chinese factory workers suggests that very high levels of BPA exposure may decrease sperm count and contribute to other sperm-related problems in men.
The findings aren't surprising. BPA—which can be found in some baby bottles and water bottles, as well the linings of food and beverage cans—is known to be a so-called endocrine disruptor that functions "like a weak estrogen" and blocks male sex hormones (including testosterone), says the lead author of the study, De-Kun Li, MD, a reproductive and perinatal epidemiologist at Kaiser Permanente's division of research, in Oakland, Calif.
But the study is notable because it's one of the first in humans to link BPA with reproductive problems. Until very recently, most of the evidence implicating BPA in health problems has come from animal or laboratory studies. (BPA has been associated with reduced sperm count in mice and rats, for instance.)
"Human studies have been the missing link," Dr. Li says.
In the new study, which appears in the journal Fertility and Sterility, Dr. Li and his colleagues collected urine and semen samples from 218 factory workers, some of whom worked in facilities that make BPA or epoxy resin and were therefore regularly exposed to very high levels of the chemical.
Compared to men whose urine was BPA-free, those who had detectable levels of BPA were four times more likely to have a below-average sperm count, three times more likely to have fewer "live" sperm than average, and two times more likely to have below-average sperm quality (motility).
“If BPA has such an impact on male sexual function, we have to wonder what else it has an impact on," Dr. Li says.
The findings don't prove cause and effect, however, and it's not clear how relevant they are for men in the U.S. who aren't exposed to unusually high levels of BPA. Although the researchers did find a connection between BPA levels and sperm problems in men who were exposed to BPA only in the general environment (rather than the workplace), it's possible that the study population differs from the U.S. population in key ways.
Still, the study seems likely to serve as ammunition for advocates and public health officials who favor restrictions on BPA.
Earlier this month, Canada became the first nation to officially declare BPA a toxic substance. Although the U.S. government hasn't taken similar action, several states have banned the use of the chemical in baby products (or have considered it) and many manufacturers have voluntarily phased out BPA from their products.