Further evidence has emerged showing that a chemical used widely in plastic packaging and the lining of drinks cans may be harmful to health.
The latest study has shown that bisphenol A (BPA) can affect the way genes work in the brains of laboratory rats, although other scientists have questioned the relevance of the findings to humans.
Researchers found that feeding BPA to pregnant rats was associated with lasting alterations to the “epigenetic” structure of genes in the brain tissue of their offspring, causing possible changes to certain aspects of sex-specific behaviour, such as chasing, sniffing and aggression.
Previous studies on laboratory animals have also pointed to a possible link between BPA and ill health but this research was criticised by other experts for using very high doses of the chemical, which would not be relevant to levels of human exposure, and to injecting the substance rather than feeding it through the diet, which is how BPA enters the human body.
The latest study by Frances Champagne of Columbia University in New York, published in the Proceeding of the National Academy of Sciences, used what the scientists said were “environmentally relevant” doses of BPA, which were fed to the rats through their diet.
The researchers concluded: “This study provides evidence that low-dose maternal BPA exposure induces long-lasting disruption to epigenetic pathways in the brain of offspring….Importantly, our findings indicate that these BPA-induced changes occur in a sex-specific, brain region-specific and dose-dependent manner.”
Professor Richard Sharpe of the Medical Research Council's Centre for Reproductive Health in Edinburgh said that although the study is well conducted there are still problems that make it difficult to extrapolate the findings to human health.
“Whilst these findings raise the possibility that comparable effects of bisphenol A could occur in humans, several factors suggest this is unlikely. First, the lowest dose used is still 10-20 times higher than normal human bisphenol A exposure,” Professor Sharpe said.
Another problem is that there were large variations in the results beween individual animals, making reproducible results questionable. A third issue was the suggestion that BPA works by interfering with the female hormone oestrogen, as oestrogen levels are much higher in pregnant women than in pregnant mice, Professor Sharpe said.
“If the effects described work through an oestrogen mechanism, they are unlikely to be human relevant because pregnancy levels of oestrogens in humans are far higher than in mice and would swamp any weak oestrogenic effects of bisphenol A,” he said.
BPA, which can interfere with the female sex hormone, is found in small quantities in most people but the levels of exposure are thought by most experts to be too low to result in biological effects. However, some researchers, particularly in the US, have disagreed with this assertion.