Previous Studies on Toxic Effects of BPA Couldn’t be Reproduced, says MU Research Team
Following a three-year study using more than 2,800 mice, a University of Missouri researcher was not able to replicate a series of previous studies by another research group investigating the controversial chemical BPA. The MU study is not claiming that BPA is safe, but that the previous series of studies are not reproducible. The MU study, published in the Proceedings of the National Academy of Sciences, also investigated an estrogenic compound found in plants, genistein, in the same three-year study.
“Our findings don’t say anything about the positive or negative effects of BPA or genistein,” said Cheryl Rosenfeld, associate professor of biomedical sciences in MU’s Bond Life Science Center. “Rather, our series of experiments did not detect the same findings as reported by another group on the potential developmental effects of BPA and genistein when exposure of young occurs in the womb.”
Creating reliable data on the effects of the chemicals on mice is important to human health since people are frequently exposed to BPA and genistein and humans share similar biological functions with mice. BPA is a chemical used in certain plastic bottles and may be found in the lining of some canned goods and receipt paper. Genistein occurs naturally in soy beans and is sold as a dietary supplement. Research by Fredrick VomSaal, professor of biological science at MU, and others suggests the chemicals may have other adverse effects on many animals, including humans.
Researcher who conducted the original series of experiments claimed that exposure to BPA and genestein resulted in yellow coat color, or agouti, offspring that were more susceptible to obesity and type 2 diabetes compared to their brown coat color, healthy siblings. However, Rosenfeld and her team did not obtain the same results when repeating the study over a three-year period.
Bisphenol A (BPA) is an industrial chemical used primarily to make polycarbonate plastic and epoxy resins – both of which are used in countless applications that make our lives easier, healthier and safer, each and every day.
It started in 2008 with plastic bottles. After a report suggested that bisphenol A – used as a sealant in food and beverage containers – might be toxic to humans, some bottle manufacturers cut the chemical out of their products. Since then, the body of research on BPA has grown rapidly but a consensus has not, as evidence has supposedly “proven” both its relative safety and its potential risk.
After failing to repeat the original experiments findings with similar numbers of animals, Rosenfeld’s group extended the studies to include animal numbers that surpassed the prior studies to verify that their findings were not a fluke and to provide sufficient number of animals to ensure that significant differences would be detected if they existed. However, even these additional numbers of animals and extended experiments failed to reproduce the earlier findings. However, the current studies demonstrate that a maternal diet enriched in estrogenic compounds leads to a greater number of offspring that express an agouti gene compared to those that do not, even though equal ratios should have been born.
A new study has reported a statistical association between urinary levels of bisphenol A (BPA) and obesity in children, but the authors acknowledge that the study does not indicate a causal relationship. They further state that their study was “at best hypothesis generating” indicating that the study results are speculative and, at most, might provide the basis for conducting additional studies.
The cross-sectional study, * the results of which were published in the Journal of the American Medical Association (JAMA), analyzed a randomly selected, national sample of 2,838 young people ages 6-19, whose urinary BPA concentration had been measured in the 2003-08 National Health and Nutrition Examination Surveys. After controlling for factors including race, age, income, caloric intake and television watching, the researchers analyzed the connections between urinary BPA concentration and body mass index (BMI). They found that higher BPA levels were “significantly associated” with BMI measures that indicated obesity.
The researchers acknowledge, however, that obesity is a complex disease that develops over time, and that they cannot infer from the study that any level of BPA intake causes obesity. This is not surprising, given the study’s fundamental limitations and that numerous other studies conducted on animals exposed to BPA have found no consistent effect on body weight.
The authors comment extensively on possible explanations for their findings. They state that the time of Urine collection might influence BPA concentration. Furthermore, they concede that they do not know what foods were consumed by the children in the study.
“Obese children may drink more canned or bottled beverages, or eat more canned food, and thus have higher urinary BPA levels,” they write. The researchers also state that the BPA-obesity correlation was found among Caucasian children but not black or Hispanic youngsters - a fact that seems to further cloud the issue of causation.
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Trasande, L, et al. Association Between Urinary Bisphenol A Concentration and Obesity Prevalence in Children and Adolescents. JAMA 2012; 308(11:1113-1121)
“This finding suggests that certain uterine environments may favor animals with a ‘thrifty genotype’ meaning that the agouti gene of mice may help them survive in unfavorable uterine environments over those mice devoid of this gene, Yet, the downside of this expression of the agouti during early development is that the animals may be at risk for later metabolic disorders, such as obesity and diabetes” Rosenfeld said. “In this aspect, humans also have an agouti gene that encodes for the agouti signaling protein (ASIP) that is expressed in fat tissue and pancreas, and there is some correlation that obese individuals exhibit greater expression of this gene compared to leaner individuals. Therefore, the agouti gene may have evolved to permit humans the ability to survive famine, but its enhanced expression may also potentiate metabolic diseases under bountiful food conditions.”
The American Chemistry Council (ACC) issued the following statement today in response to a European Food Safety Authority (EFSA) announcement about consumers and the safety of bisphenol A (BPA):
“For the third time since 2007, and as a result of a comprehensive review of more than 800 recent studies, EFSA has again confirmed that bisphenol A (BPA) is safe for use in products that come in contact with food,” said Steven G. Hentges, Ph.D., of the American Chemistry Council.
“Consumers around the world can be reassured that EFSA’s intense scientific scrutiny continues to reaffirm the safety of BPA in food contact applications, and again concludes that established safe intake levels for BPA provide a sufficient margin of safety for protection of consumers, including for infants and young children,” Hentges said.