In order to find out where the butylparabens in the pregnant women’s urine came from in the first place, the researchers combed through the questionnaires completed by the participants in the LINA study for details of the cosmetics used during pregnancy. “Using the ToxFox app developed by BUND enabled us to easily and quickly check whether parabens were among the ingredients of the respective cosmetics products”, Polte explains. “And high concentrations of parabens in the mothers’ urine were indeed associated with the use of cosmetics containing parabens – particularly those that remained on the skin for a protracted period of time, such as creams or body lotions.”
But how does the use of creams containing parabens by expectant mothers tie in with the child’s future overweight? To track down the underlying mechanisms, the team of researchers firstly used cell cultures to examine whether fat cells themselves react to high concentrations of butylparaben. “Butylparaben did not cause an increase in the size of the fat cells or the stored fat”, Lehmann reports. “It was evident that the differentiation of fat cells was not impacted by the parabens.” Something else had to be behind the children’s weight gain. In collaboration with colleagues from the Medical Faculty at Leipzig University, the researchers used a mouse model to simulate exposure to parabens during pregnancy. In this model, mice absorbed butylparabens through the skin. “Just as in the LINA study, the female offspring here also demonstrated increased weight gain”, says Polte. “And they ate significantly more than the offspring of mice from the control group.” Consequently, the researchers suspected that parabens might exert an influence on how hunger is regulated in the brain, and performed a closer examination of key genes in the hypothalamus of the mouse offspring.
It became apparent that a gene by the name of proopiomelanocortin (POMC) that is decisive in controlling the feeling of hunger was down-regulated in the brains of the young mice. Further investigations at a genetic level revealed that an epigenetic modification was responsible for this by preventing the corresponding POMC gene from being read. “The influence of parabens during gestation obviously gives rise to epigenetic modifications in the offspring that permanently disrupt the regulation of the natural feeling of satiety. This means that they have a higher food intake”, Polte explains. Therefore, parabens seem to constitute as a risk factor during pregnancy for the occurrence of children`s overweight. However, also other factors play an important role in weight gain, such as a hypercaloric diet and lack of exercise.
So far, the researchers have not been able to come to any conclusions on how stable the epigenetic modifications are or whether they can be passed on to the next generation. However, they are already able to make an unambiguous recommendation based on the findings so far: “Bearing in mind the future health of their children, expectant mothers really should use paraben-free products during the sensitive periods of pregnancy and breastfeeding”, says Lehmann. Many cosmetic products are already declared to be paraben-free; otherwise, this information can be obtained from the list of ingredients or using the ToxFox app, for instance.” The researchers will continue to search for further potential effects of parabens in future investigations. “Epigenetic modifications that relate to the regulation of satiety are only one possible end point”, says Polte. “Intergenerational effects of environmental factors have often been underestimated to date. We hope that our research will help to focus greater attention on such factors in future.”
Beate Leppert, Sandra Strunz, Bettina Seiwert, Linda Schlittenbauer, Rita Schlichting, Christiane Pfeiffer, Stefan Röder, Mario Bauer, Michael Borte, Gabriele I. Stangl, Torsten Schöneberg, Angela Schulz, Isabell Karkossa, Ulrike E. Rolle-Kampczyk, Loreen Thürmann, Martin von Bergen, Beate I. Escher, Kristin Junge, Thorsten Reemtsma, Irina Lehmann, Tobias Polte (2020): Maternal paraben exposure triggers childhood overweight development, Nature Communications; doi: https://doi.org/10.1038/s41467-019-14202-1