The study, thought to be the first to measure effects of BPA on human male reproduction, was the work of lead author Dr De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, California, and was published online in the 10 November advance access issue of the journal Human Reproduction.
The authors wrote in their background information that animal studies on mice and rats have already suggested that BPA could interfere with hormones in humans, but evidence from human studies was lacking.
For this 5-year study, which was funded by the US National Institute of Occupational Safety and Health, Li and colleagues recruited 634 men working in factories near Shanghai in China.
230 of the men worked in factories where they were exposed to very high levels of BPA, and 404 worked in factories with no BPA present. The researchers matched them by age, education, gender and employment history.
The men exposed to high levels of BPA worked in four factories: one that made BPA and three others that used it to make epoxy resin. They had various jobs such as maintenance workers, packagers, technical supervisors and laboratory technicians.
The researchers wrote that the BPA levels these men were exposed to were 50 times higher than that experienced by the average American male in the US.
The factories with no BPA exposure made construction materials, water supplies, machinery, garments, textiles, and electronic products.
Li and colleagues measured BPA exposure by taking spot air samples, personal air sample monitoring and walk-through evaluations. They also reviewed factory records, interviewed factory leaders, and interviewed workers about personal hygiene, use of protective equipment and exposure to other chemicals.
A subgroup of workers also provided urine samples so the researchers could verify that the men working in factories where they were exposed to BPA had higher levels of BPA in their bodies.
To assess sexual function, the researchers interviewed all the men using questions from a standard inventory that measures four categories of sexual function: erectile function, ejaculation capability, sexual desire, and overall satisfaction with sex life.
After adjusting for age, education, marital status, current smoking status, a history of chronic diseases and exposure to other chemicals, and employment history, the researchers found that:
- BPA-exposed workers had a significantly higher risk of sexual dysfunction compared to the unexposed workers.
- BPA-exposed workers had a nearly four-fold increased risk of reduced sexual desire and overall satisfaction with their sex life.
- They also had a greater than four-fold increased risk of erection difficulty, and more than seven-fold increased risk of ejaculation difficulty.
- There was a dose-response relationship between increased level of cumulative BPA exposure and higher risk of sexual dysfunction.
- Compared to unexposed workers, BPA-exposed workers reported significantly higher frequencies of reduced sexual function within one year of starting work in a BPA-exposed factory.
"Our findings provide the first evidence that exposure to BPA in the workplace could have an adverse effect on male sexual dysfunction."
Li told the press that:
"Because the BPA levels in this study were very high, more research needs to be done to see how low a level of BPA exposure may have effects on our reproductive system."
"This study raises the question: Is there a safe level for BPA exposure, and what is that level? More studies like this, which examine the effect of BPA on humans, are critically needed to help establish prevention strategies and regulatory policies," said Li.
The researchers explained that BPA is thought to disrupt reproductive hormones in both men and women. This is the first study to provide the evidence that could be lacking as the US Food and Drug Administration and other federal bodies examine this controversial subject.
BPA has been in commercial use for half a century and is used to make polycarbonated plastics and epoxy resins found in baby bottles, plastic containers, the lining of cans used for food and beverages, dental sealants, spectacle lenses, CDs, DVDs, and a range of household electronic goods.
Li suggests their findings also imply that BPA may have effects beyond male sexual dysfunction. Male sexual dysfuntion could be an early indication of diseases that are more difficult to study, such as cancer and metabolic diseases.
"Occupational exposure to bisphenol-A (BPA) and the risk of Self-Reported Male Sexual Dysfunction."
D. Li, Z. Zhou, D. Qing, Y. He, T. Wu, M. Miao, J. Wang, X. Weng, J.R. Ferber, L.J. Herrinton, Q. Zhu, E. Gao, H. Checkoway, and W. Yuan.
Hum. Reprod. Advance Access published on November 10, 2009.
Source: Kaiser Permanente.