Exposure to a chemical found in food packaging and other plastics, BPA, can reduce the quality of men's semen, according to the findings of a five-year study and one of the few involving humans rather than animal models.
"This study counters the argument that only highly exposed populations are affected," said study author Dr. De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, Calif.
"You can be exposed from the workplace. You can be exposed from consumer products. It doesn't really matter. Ultimately it will reflect in your urine," he said.
The researchers suggest findings should apply to Americans since even low levels of BPA exposurecomparable to men in the general U.S. population were found to have an adverse effect on sperm quality and quantity.
The study, based on measurements from 218 Chinese workers, found a link between high concentrations of BPA, or Bisphenol A, in men's urine and lower sperm counts, as well as poor-functioning sperm cells.
The study began with 514 workers recruited from epoxy resin factories in China in 2004. Only 218 of the participants ended up submitting both urine and semen specimens for the final assessment. Researchers measured semen quality by examining factors like concentration, vitality, motility (movement), total sperm count and morphology (size and shape).
Men exposed to BPA at work and who showed detectable urine BPA had more than three times the risk of lower sperm concentration and vitality than men with no detectable urine BPA. The former group also had more than four times the risk of lower sperm count and more than twice the risk of lower sperm motility.
Li and his team discovered a similar association between men with low BPA exposure from environmental sources and raised urine BPA levels and decreased semen quality.
No correlation was shown between urine BPA and semen volume or shape.
Animal studies already have shown that BPA is a hormone disruptor that can affect male reproductive organs, including the epididymis (coiled structure in the scrotum) and testes. However, there have been few findings regarding the chemical’s influence on humans, including a recent study on male sexual dysfunction by Li and his researchers.
"Our study shows that BPA could lead to pathological changes to human organs — semen quality, in this case," Li told LiveScience. "In addition, this new finding of the detrimental effect of BPA exposure on semen quality raises the bar of BPA toxicity."
How this affects Americans
Bisphenol A can be found in food packaging (the primary source of human exposure), DVDs, paper coatings, and automotive equipment, among other products. Releases of the chemical to the environment exceed 1 million pounds per year, according to a recent report by the Environmental Protection Agency.
Gail Prins, a reproductive physiologist at University of Illinois College of Medicine, who was not involved in the study, said the finding is important though unsurprising and that it emphasizes the importance of animal model research in predicting outcomes in human populations.
"Evidence has indicated that for the past few decades, sperm counts have been declining in some human populations — and that this might be related to exposures to endocrine-disrupting chemicals such as BPA is very reasonable," Prins said. "I strongly believe that the U.S. should take measures to reduce the use of this chemical, since levels build over time."
Current regulations should reflect more recent findings, said John Meeker, an assistant professor of environmental health sciences at the University of Michigan, who was not involved in Li's study.
"We know that the majority of Americans have measurable levels of BPA in their bodies," Meeker said. "Since new research results in both humans and animals are currently being published nearly every day, policies should be re-evaluated using the most up-to-date information available."
The findings suggest semen quality and male sexual dysfunction could be used as early indicators of for harmful BPA effects than other diseases, such as cancer, the researchers say.
Li and colleagues plan to examine the effects of BPA exposure during pregnancy. Though Li warned that further research is needed, he advised individuals to make informed decisions regarding products that may contain BPA.
"As average consumers, we do not need to wait for regulatory agencies' decision. We can take precautionary steps to avoid the exposure to BPA in our daily life," he said. "Besides, there is no downside to avoiding BPA."
The study was published in the Oct. 28 issue of the journal of Fertility and Sterility. The work was funded by the U.S. National Institute of Occupational Safety and Health.