While environmental groups have sounded the alarm about the presence of bisphenol-A, or BPA, in products such as infant formula, baby bottles and other plastics, a new study provides some of the first evidence that the chemical can be harmful to humans, linking it to sexual dysfunction in men in high doses.
Researchers looked at 550 factory workers in China, some of whom were exposed to BPA as part of their job, and found that men who worked with BPA were four times more likely than their counterparts who did not work with the chemical to report some level of sexual dysfunction.
"The study certainly provides the human evidence to confirm animal studies, but one study is not going to answer any questions," said Dr. De-kun Li, the study's lead author and a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, Calif.
Li noted that while BPA's presence has been confirmed in a number of consumer products, all studies before now had only shown harm in nonhuman populations.
"Up to this point, it's largely, basically animal studies," said Li, explaining that little has been done about BPA because of a lack of studies in people.
"There has been no human studies, at least in the context of the male reproductive system, so this has been dismissed by some critics," he said of the potential harms BPA may pose.
But Li acknowledged that the current study will likely do little to change policy, since the levels of BPA were much higher than those encountered by the average person in his or her daily life. The average worker exposed to BPA had levels roughly 50 times higher than the average person.
"At this point ... we don't know the safety of the lower level," he said, but noted that people do not need to worry too much. "We don't have to be alarmed and go crazy."
In the study, 15.5 percent of men exposed to BPA complained of erectile dysfunction more than half of the time, while only 4.4 percent of men not exposed to BPA had the same complaint. Meanwhile, 13.9 percent of men with BPA exposure on the job complained of difficulty ejaculating, while only 2.5 percent of men without the on-the-job BPA exposure had the same complaint.
While previous reports on BPA have relied heavily on animal studies, none have promoted a ban on the substance.
The National Toxicology Program, part of the National Institutes of Health, considers BPA to be a substance of "some concern" -- the third level of a five-part scale ranging from "serious concern" to "negligible concern."
"There are insufficient data from studies in humans to reach a conclusion on reproductive or developmental hazards presented by current exposures to BPA, but there is limited evidence of developmental changes occurring in some animal studies at doses that are experienced by humans. It is uncertain if similar changes would occur in humans, but the possibility of adverse health effects cannot be dismissed," the agency writes about BPA in its factsheet.
It is unclear exactly how BPA would cause sexual dysfunction, according to Dr. Michele Marcus, a professor and interim chair in the department of epidemiology and environmental health at Emory University's Rollins School of Public Health. One possible explanation, she said, is that BPA, a known endocrine disruptor, can mimic estrogen and block some effects of testosterone.