A five-year study of factory workers has linked the controversial chemical BPA (Bisphenol-A), which is found in food and drink cans, plastic bottles, and many other everyday products, to poor sperm quality.

The study of 514 factory workers in China, conducted by investigators from the research division of Kaiser Permanente, a leading US provider of health care and not-for-profit health plans, is the first to report an adverse association between BPA and semen quality. A paper on the research is about to be published in the journal of Fertility and Sterility.

Lead author Dr De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente’s Division of Research in Oakland, California and colleagues, found that the workers with higher urine levels of BPA had between two and four times the risk of having poor semen quality, including low sperm count, motility, vitality and concentration, compared with those who had low urine BPA.

Li told the media that:

“Compared with men without detectable urine BPA, those with detectable urine BPA had more than three times the risk of lowered sperm concentration and lower sperm vitality, more than four times the risk of a lower sperm count, and more than twice the risk of lower sperm motility.”

He said there was a similar “dose-response” link in the workers whose environmental exposure to BPA was comparable to that of men in the general US population.

For the study, 514 (58 per cent) of the 888 eligible workers agreed to participate. Of them, 218 workers provided both urine and semen samples and were included in the final analyses.

Through in-person interviews, participants also answered demographic, health and lifestyle questions from which the researchers assessed potential risk factors that could affect influence semen quality, such as recent exposure to a heat source (eg a steam bath), smoking behavior, use of alcohol, occupational history, chronic diseases, history of sub-fertility, and exposure to other chemicals and heavy metals.

Even though the sample size of the men who were exposed to low levels of BPA was not high, the inverse link beween increased urine BPA and decreased sperm concentration and total sperm count remained statistically significant, said the researchers.

Urine BPA was not, however, linked with semen volume or abnormal sperm structure or shape.

The finding adds to a mounting pile of evidence questioning the safety of BPA, an organic chemical widely used to make polycarbonate plastic and epoxy resins, and found in plastic containers, baby bottles, the linings of food and drink cans, and in dental sealants. Earlier this month, Canada became the first country to declare BPA a toxic substance.

This is the third study that Li and colleagues have published recently on the effect of BPA in humans. The first found that exposure to high levels of BPA at work increased risk of reduced sexual function in men (Nov 09, Oxford Journals Human Reproduction) , and the second found that increasing amounts of BPA in urine are linked with worsening male sexual function (May 10, Journal of Andrology).

Previous animal studies have also shown a link between BPA and adverse effects in male reproductive systems in mice and rats.

Some researchers believe BPA is a human endocrine disrupter that interferes with hormones in male and female reproductive systems.

This new study may plug the gap in evidence that has been missing in the deliberations of the US Food and Drug Administration and other government panels over this controversial substance.

Li said these findings may also point to problems beyond the male reproductive system: semen quality and male sexual dysfunction could be early signs of diseases that are harder to study, such as cancer or metabolic diseases, he added.

The study was funded by the US National Institute of Occupational Safety and Health.

— Fertility and Sterility

Source: Kaiser Permanente.

Written by: Catharine Paddock, PhD