Parabens are used as preservatives in cosmetics. If pregnant women use cosmetics containing parabens that remain on the skin for protracted periods, this may have consequences for their child's subsequent weight development. This is demonstrated in a study published in the journal Nature Communications by researchers from the Helmholtz Centre for Environmental Research (UFZ) in collaboration with colleagues from Leipzig University, Charité University Hospital in Berlin and the Berlin Institute of Health (BIH). Based on data from the LINA mother-child study, they were further able to identify epigenetic modifications that are triggered by parabens and interfere with the natural regulation of satiety in the brain.
Methylparaben, propylparaben, butylparaben - these and similar are the names of parabens commonly used as preservatives. Substances that are used in creams and body lotions to combat microbes can have an undesirably side-effect, however. "If pregnant women absorb parabens through the skin, this can lead to overweight in their children", says UFZ environmental immunologist Dr Tobias Polte. The starting point for the investigations was the LINA mother-child cohort study, a long-term study conducted by the UFZ to examine the significance of environmental factors in sensitive periods of childhood development for the later occurrence of allergies and respiratory diseases or overweight.
We initially wanted to find out whether the parabens detected in urine from expectant mothers from the mother-child cohort had an impact on the development of their children's weight". In doing so, we discovered a positive correlation between the concentrations of butylparaben in the mothers' urine and a higher body-mass index of their children - particularly of the daughters - until their eighth birthday."
Prof. Irina Lehmann, former UFZ researcher, currently at the Berlin Institute of Health (BIH) and at Charité - Berlin University Hospital
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 bring about an increase in the size of the fat cells, nor did the fat cells store more fat than otherwise", 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 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 cosmetics 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."
Leppert, B., et al. (2020) Maternal paraben exposure triggers childhood overweight development. Nature Communications. doi.org/10.1038/s41467-019-14202-1.