Andy Ho, Straits Times 8 Nov 08;
BACK in August, the United States Food and Drug Administration (FDA) declared the chemical used to make plastics hard 'non-toxic'. Called bisphenol-A or BPA, the chemical is used in baby bottles, bottles for water and beverages, the coatings of cans used to pack infant formula and other foodstuff, the linings of medical devices and water supply pipes, and so on.
Studies by the Centres for Disease Control and Prevention show that BPA is found in the bodies of an amazing 93 per cent of US residents over the age of six years. If it is really non-toxic, then many can heave a sigh of relief.
In coming to its conclusions, however, the FDA passed over 100 studies. The National Toxicology Programme, a US government-funded initiative tasked to provide unbiased evaluations of the scientific evidence on a particular issue, then re-examined all BPA studies.
The FDA had used only three studies, all funded by the chemical industry, clearly an interested party. It was also revealed that the chair of the FDA panel reviewing BPA safety had failed to disclose a US$5 million (S$7.5 million) gift from the founder of a medical equipment-making company.
The chairman - a professor of toxicology at the University of Michigan, Ann Arbor - had been repeatedly told by that interested party that BPA was 'perfectly safe'. An inquiry into the matter was initiated by the US Congress.
Last Wednesday, the National Toxicology Programme reported that its review had led it to conclude that BPA might lead to brain damage as well as heightened risks of cancer. And last Friday, a panel of scientists the FDA itself had convened to review its August report concluded it was in agreement with the programme's assessment of the matter.
The panel noted that studies not funded by industry did show that BPA might harm children, even at levels 10 times lower than what the FDA had deemed safe. But the FDA stood its ground, insisting that BPA was non-toxic. More studies were promised but, meanwhile, BPA would continue to be allowed on the shelves.
The National Toxicology Programme noted that exposure to BPA was widespread - in Europe and Asia, as well as in the US - frequent and continuous. As the chemical does not remain in the body for long, its widespread discovery means that people's exposure to it is recurring. Moreover, the levels are also rising, with median levels of exposure having doubled between 1994 and 2004.
Recognising that the data was by no means complete, comprehensive or completely consistent, the programme concluded that 'the possibility that bisphenol-A may alter human development cannot be dismissed'. This was so especially because BPA can be found in high levels in the blood of pregnant mothers, the placenta, cord blood and breast milk.
In the lab, the chemical can permanently reorganise brain circuits in female rats to make them more male-like in their non-reproductive behaviour. These include how they deal with stress or anxiety, seek novelty, and respond to attention or motivation. Female lab rats apparently differ in such behaviours from male ones.
Without long-term observational studies in humans, it is hard to say whether BPA causes equivalent changes in the human infant brain. Overall, the programme concluded that there was cause for 'some concern' that exposure in the womb and in early infancy might lead to changes in infant brain structure and behaviour.
Elsewhere, in other tissues, BPA may act like a weak female hormone instead. In this connection, the programme was a bit concerned that some of the lab studies showed BPA might lead to pre-cancerous changes in the breast glands of females.
Other studies on lab animals also caused the programme to express concern that BPA might also induce pre-cancerous changes in the prostate in males.
All these are animal studies from which the programme has drawn conclusions about the chemical's probable impact on human health. But the state of knowledge about the effects of BPA in humans is much more rudimentary.
The first epidemiological study of BPA in humans has only just been just published in the Journal of the American Medical Association in September. But in this study, other diseases than those the animal studies had pointed to were implicated instead.
The study found that BPA exposure in the US population exceeded the upper limit set by the US Environmental Protection Agency. These high BPA levels were found to be significantly associated with heart disease and diabetes.
People exposed to a lot of BPA tripled their risk for heart disease. They were also 2.4 times more likely to develop diabetes. And their liver function tests tended to be abnormal as well.
One lesson that can be drawn at this juncture is that animal models suggest BPA may cause significant health problems while more epidemiological studies in humans might point to the same or other problems. All in all, the balance of evidence makes it hard to agree with the FDA that BPA is assuredly non-toxic to humans.
In April, Canada banned the use of BPA in infant milk bottles. Perhaps its lead is worth following as soon as possible.
