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.
Because his study does not provide answers for the average person looking to know if BPA will do him or her harm, Li said any steps would be strictly precautionary.
"It's certainly based on everybody's risk tolerance level," he said, adding that avoiding BPA "would be my advice. It's unlikely the regulatory agencies will do anything yet, because they would like to see the evidence from human studies."
"If there's credible evidence of the potential of harm, why not look for a safer alternative?" said Kathy Gerwig, vice president for workplace safety and environmental stewardship officer at Kaiser Permanente.
Gerwig said that while BPA has not been proven harmful, there were steps consumers could take if they wanted to reduce their BPA exposure.
"If you're going to buy a rigid plastic bottle, look for one that is BPA-free," she said.
Second, Gerwig recommended avoiding canned foods, which contain BPA in the linings, something she said would be advantageous because it promoted eating fresh foods.
Third, she said, "It's a smart decision to stay away from heating foods in the microwave in plastics."
Given the high levels of BPA industrial workers were exposed to in the study, many may be tempted to dismiss the much lower levels of exposure the average person experiences.
But paradoxically, lower levels may be more harmful, explained Dr. David Ozonoff, a professor of environmental health at the Boston University School of Public Health.
"These are hormone-like chemicals, and your body is used to responding to hormones at really low levels," he said.
He compared it to two friends in a crowded bar trying to speak, who cannot do so because of the noise. In those circumstances, the noise may be cancelled out, while in a quieter room, that message may be heard and listened to.
For a signal that has the potential to be disruptive, said Ozonoff, a signal that can be "heard" can be more dangerous than a large number of signals that can be dismissed as static.
"That's one of those things that we worry about," he said.
Ozonoff said the study is still open to interpretation, and further studies will need to be done for any conclusions to be drawn about the potential harmfulness of BPA.
However, he concluded, "There's nothing about this that should give any comfort to someone that thinks BPA is OK."
Michelle Schlief and Cari Nierenberg contributed reporting.