The Interplay Between Environmental Chemical Exposures and Obesity Proceedings of a Workshop (2016) / Chapter Skim
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3 Developmental View of the Role of Chemical Exposures and Obesity
3 Developmental View of the Role of Chemical Exposures and Obesity
Pages 21-44
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From page 21... ...
In her research, Valvi focuses on whether early life exposures to environmental chemicals influence children, with a special interest in studying obesity and metabolic diseases. Valvi's presentation detailed evidence from birth cohort studies evaluating the impact of prenatal and postnatal exposures to persistent organic pollutants (POPs)
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From page 22... ...
is a Spanish research network focused on studying environmental pollutants in the air, water, and diets of children and how these pollutants affect children's health, starting during pregnancy and continuing through childhood development until the end of adolescence. For more information, see http://www.proyectoinma.org/presentacion-inma/en_index.html (accessed August 3, 2015)
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From page 23... ...
Animal studies have further shown that POPs, like other endocrine disrupters, may exhibit different effects at lower and higher doses of exposure. From the human studies available, most studies are birth cohort studies that evaluated exposures during pregnancy and looked for associations with childhood obesity; almost none of these studies evaluated postnatal exposure.
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From page 24... ...
The concentrations of POPs in expectant mothers were measured using serum samples collected in pregnancy and cord blood samples collected at birth. Exposure to a wide list of other environmental pollutants was also measured by analyzing biological samples (blood, urine, hair)
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From page 25... ...
The INMA researchers further evaluated the associations between exposures to multiple chemicals, including 27 different endocrine disrupters whose levels were measured in maternal biological samples collected in pregnancy, and child BMI at age 7 years using principal component analyses. The findings from this multipollutant approach showed that associations between POPs and childhood obesity remain robust after accounting in the models for exposure to other chemicals thought to be linked to childhood obesity, including BPA (Valvi et al., 2013)
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From page 26... ...
An advantage of this study is that exposure to POPs as well as other environmental contaminants was measured both prenatally and postnatally by the use of serum samples collected from mothers and children. The study found some evidence that prenatal exposure to POPs is associated with an increased risk of obesity at 7 years of age (TangPéronard et al., 2014)
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From page 27... ...
Valvi answered that they have data on aryl hydrocarbon receptor activity but have not yet finalized the analysis. She also suggested that the effects of dioxin-like compounds may be more complex than what people may think because they act through a number of receptors, not just the aryl hydrocarbon receptor, which has so far been the main focus in human studies.
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From page 28... ...
Estimates of the effect of the associations with prenatal exposures do not usually change when such dietary factors are taken into account, she said, but she indicated that they assessed the diet using food frequency questionnaires, which is not the most accurate method to use for dietary assessment. ENDOCRINE-DISRUPTING CHEMICALS, ONSET OF PUBERTY, AND OBESITY The second speaker was Frank Biro, the director of research in adolescent and transition medicine at the Cincinnati Children's Hospital Medical Center and a professor in the Department of Pediatrics at the University of Cincinnati.
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From page 29... ...
In 1997, Matkovic and colleagues pointed out that the relationship was actually between leptin, a hormone produced by fat cells, and earlier menarche. They reported that for every increase in the serum leptin concentration of 1 nanogram per milliliter, the age of menarche dropped by 1 month (Matkovic et al., 1997)
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From page 30... ...
But, Biro said, later studies confirmed their data indicating the onset of breast development in girls earlier than had previously been thought. Then, in late 2013 Biro and colleagues published the results of a similar analysis done with girls who participated in the Breast Cancer and Environmental Research Program (BCERP)
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From page 31... ...
. In the modell, various expo osures could llead to increaased obesity aand increassed amounts of visceral fat, f includingg exposures cconsisting off a consisttent energy im mbalance, en ndocrine-disrupupting chemiccals, and inadde
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From page 32... ...
Then he recalled that obese women have higher rates of breast cancer and that the mechanism that has been proposed to explain that is that in these women's fat cells, aromatase is converting adrenal androgens into estrogen, leading to higher levels of estrogens and an increased risk of breast cancer. So, Biro said, what he believes that this study shows is that while the overweight and obese girls are not getting a big increase in estradiol levels, they do have high local levels of estrogen because of the conversion of adrenal androgens in their fat cells without elevated serum estrogen levels.
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From page 33... ...
For example, one study found that soy formula consumption during infancy leads to earlier menarche, while two others found that soy consumption in childhood led to a delay in the onset of breast tissue development. The timing may be the critical piece, he said.
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FIGUR RE 3-2 Delay yed appearancce of pubic haair in girls exxposed to higghmolecuular-weight phtthalates. NOTE: DEHP = bis(2 2-ethylhexyl)
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From page 35... ...
Biro responded that he and his colleagues have collected a vast amount of data on the girls in their studies: dietary patterns, anthropometric examinations, urine and serum biomarkers, sex steroids, fasting insulin, and glucose, among others. "Right now, we are dealing with two and three parameters at a time," he said.
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From page 36... ...
The children were up to 6 or 7 years of age at follow-up. The OBELIX epidemiologists worked with researchers across Europe who were carrying out studies on their own birth cohorts to expand the number and breadth of studies.
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From page 37... ...
The complementary animal studies were designed to be very similar in design to the human studies. The mice were exposed to environmental chemicals through their mothers' blood supply during gestation and for another 3 weeks after birth through breast-feeding until the animals were weaned.
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From page 38... ...
The researchers showed that BDE 47 causes a decrease in the methylation of the promoter sequence of the PPARγ2 gene, which leads to increased expression of the gene and increased fat cell differentiation, so this appears to be the mechanism by which BDE 47 leads to an increased number of fat cells. In conclusion, Legler said that the OBELIX project provided evidence that endocrine-disrupting chemicals do indeed play a role in obesity, affecting growth and metabolic pathways.
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From page 39... ...
It is possible to stain a young fish with a lipid stain that causes fat cells to stand out and then watch as the fat tissue develops. The research on the zebrafish has shown that certain environmental chemicals, such as flame retardants and UV filters, disturb both the metabolism and the circadian rhythms in the exposed fish.
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From page 40... ...
Legler responded that in the European studies there were essentially no women who did not breast-feed, so the only related factor that could be examined was the amount of time that the children were breast-fed. Legler added that there was a close relationship between the amount of prenatal exposure to a particular chemical and the amount of postnatal exposure through breast-feeding, so it was impossible to completely isolate the effects of the two types of exposures.
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From page 41... ...
Valvi responded that a number of studies indicate that prenatal exposure to various environmental chemicals may increase the child's risk for diabetes later in life. "And if prenatal exposure can increase the risk during postnatal life," she said, "why would not exposing the mother increase the risk for diabetes appearing during pregnancy?
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From page 42... ...
Food and Drug Administration asked if the method of delivery -- naturally versus by cesarean section -- has any effects on obesity. Valvi responded that the type of delivery has been associated with both birth weight and later metabolic risk.
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From page 43... ...
2012. Birth weight and prenatal exposure to polychlorinated biphenyls (PCBs)
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From page 44... ...
2014. Prenatal exposure to persistent organic pollutants and rapid weight gain and overweight in infancy.
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