Overeating and obesity can explain many of the medical disorders that have been blamed on a plastics chemical found at low levels in the human body, scientists said today.
A number of studies have suggested a link between bisphenol A (BPA), which is widely used in the plastic packaging, and illnesses ranging from diabetes to infertility, but the association does not mean that the chemical actually causes these disorders, they said.
A more likely explanation is that obese people who overeat - and who develop chronic illnesses as a result - are also more likely to have raised levels of BPA in their bloodstream from plastic food packaging, said Professor Richard Sharpe of the Medical Research Council’s Centre for Reproductive Health in Edinburgh.
“Studies consistently show an association between higher BPA exposure and Western disorders such as obesity, type-2 diabetes, liver and cardiovascular diseases,” Professor Sharpe said.
“There are numerous such studies, so numerous that we have to accept that the associations are real but this does not mean they represent cause and effect,” he told the American Association for the Advancement of Science meeting in Boston.
“None of these studies actually shows that bisphenol A exposures causes the disorders, the exposure is simply associated with occurrence of the disorders,” he said.
“If this association was due to cause and effect, it would mean that bisphenol A was incredibly potent and toxic, and this does not agree with published studies. This possibility therefore seems illogical,” he added.
An alternative explanation is that there is a third element that is actually responsible for the health problems and that it is associated with an increase in exposure to bisphenol A, Professor Sharpe told the meeting.
“I will suggest that this third factor is diet, or more accurately a modern Western diet, because we know that such as diet is associated with all the disorders [linked with BPA],” he said.
Studies have shown that diet accounts for about 95 per cent of the BPA levels in the body but these can be lowered by two thirds if people eat food that is freshly sourced rather than wrapped in plastic packaging, he said.
“My hypothesis is that a modern Western diet determines the level of BPA exposure – the more of it you eat, the more BPA you're exposed to – with the result that over-eating causes obesity etc, but also causes higher BPA exposure,” Professor Sharpe said.
“If this interpretation is correct, it means that a Western, poor diet is responsible on the one hand for causing the disorders and on the other hand for causing increased exposure to bisphenol A, [which is] innocently associated with the disorders as a result,” he said.
“The attraction of this hypothesis is that it fits the available facts whereas the possibility of bisphenol A causing the disorders does not fit the facts - it fails because of our exceedingly low exposure level,” he added.
Some scientists have suggested that BPA has an effect on the human body by mimicking the effect of female oestrogens, which could account for increase in infertility and other reproductive problems in men, they have argued.
However a review of 150 published studies on BPA has concluded that the concentrations of the chemical found in the human body are far too low for them to mimic oestrogens, said Justin Teeguarden of the Pacific Northwest National Laboratory in Richland, Washington.
“At these exposure levels, exposure to BPA can’t be compared to giving a baby the massive dose of oestrogens found in a birth control pill, a comparison made by others,” Dr Teeguarden said.
“Human internal exposures to BPA are below levels we would expect to cause toxicity in the general population and children,” he said.