More evidence has emerged that danger-chemical-du-jour bisphenol-A causes reproductive problems for human males.

Pressure is growing on regulators to clamp down on ‘BPA’, but human studies on its impact on health are relatively few and far between. Canada recently became the first country to declare BPA ‘toxic’.

De-Kun Li, an epidemiologist at Kaiser Permanente’s Division of Research in Oakland, California, says that while his new work may not provide enough evidence to ban BPA, consumers should now consider taking steps to limit their exposure.

Earlier this year, another team found a “preliminary association” between BPA and DNA damage in sperm, adding to previous evidence from animal studies that linked the chemical to fertility problems.

Writing in Fertility and Sterility, Li’s team say they have now obtained “the first piece of epidemiologic evidence” showing BPA impacts on human semen quality. Their study of 514 factory workers in China found that those with a detectable level of the chemical in their urine had an increased risk of lower semen quality than their non-exposed contemporaries.

“When you see this kind of association with semen you have to wonder what else BPA has an effect on,” says Li. As a precautionary principle, he adds, “Everybody should avoid BPA as much as you can.”

Li’s team also demonstrated a linear dose-response relationship. They note that the relationship between increased BPA levels and decreased semen quality was observable even among people with levels of the chemical lower than the average level found in the US population (ie – excluding those with high levels of exposure via their work environments from the calculation).

As Li’s paper notes, BPA is detectable in most of the US population. This latest paper is the third in a series, with the previous two both showing links between the molecule and sexual problems.