A Spanish research project tracking children from the womb to teenage years showed that most were more likely to be at risk of developing a metabolic disease as adults if their mothers were more exposed to certain pollutants during pregnancy, underscoring the need for policy to better regulate the chemicals.
The findings, published March 9 in Environment International, described a new association between prenatal pollutant exposure and adolescents' risk factors for developing metabolic disease in the future. Looking to an "Environment and Children" birth cohort formed in Spain between 1997 and 1998, the researchers expanded on past work, including their own, to show that this risk can be carried on from childhood.
"Up to now, this association has been studied in children, but it has not been studied in adolescents," study author Nuira Güil, a Ph.D. student at the Barcelona Institute for Global Health, said in an interview with The Academic Times.
Past work regarding this association in humans focused on children partly because they are the most vulnerable. The new work similarly looked to measure exposure to these chemicals in pregnancy, one of the most critical time periods for studying developing diseases, as organs have not yet been formed.
"This time window is very vulnerable," Güil added.
Similarly, adolescence is a sensitive period during which there are many hormone changes and rapid increases in fat mass. Güil, a human biologist, argued that results could be further translated to adulthood.
That's because adolescent cardiometabolic status examined in the study, including factors such as blood pressure levels, also "tend to track from adolescence into adulthood," Güil said. This status is "an indicator to see whether these adolescents are at risk of, maybe in some years or decades, developing metabolic syndrome diseases," including obesity, hypertension and Type 2 diabetes, she added.
The study assessed the presence of the persistent organic pollutants hexachlorobenzene and dichlorodiphenyltrichloroethane, also called "forever chemicals" because they are resistant to environmental degradation via chemical, biological and photolytic processes.
It builds on evidence, such as experimental studies with cells and animals in the laboratory, showing that the chemicals have an impact not just on obesity, especially in the areas of adipose tissue, but also in blood pressure. These chemicals mimic or block hormones' natural actions because the body identifies them as hormones.
The study also coincides with increases in the prevalence of metabolic diseases in adults and children globally, with obesity, insulin resistance, high blood pressure and hypertension being the main risk factors for adult metabolic syndrome.
The cohort included 405 women on the Spanish island of Menorca who were at least 16 years old and in their first pregnancy. Researchers analyzed cord blood samples to examine the history of exposure to one or more of the chemicals, mainly pesticides. They then followed the children until they were 18 years old.
The researchers measured markers for body mass index, waist-to-height-ratio, body fat percentage and blood pressure, examining how pollutant exposure affected these factors.
"What was surprising was that we had used many markers, and we see that the results are consistent," Güil said. Risk of adverse outcomes was greater among all those whose mothers had been more exposed to the pollutants.
Prenatal exposure to some of these chemicals was associated with higher body mass index and body fat percentage in childhood and adolescence. It was also associated with higher systolic and diastolic blood pressure levels, cardiometabolic risk and cholesterol levels in adolescents.
"Results are similar across these different health outcomes," Güil said.
The results established a connection between children's exposure to the pollutants in their prenatal stage and a higher risk of developing adult metabolic syndrome as adolescents, with 379, or 78.6% of the children displaying at least one of the measures, such as high blood pressure.
The children were between the ages of 4 and 18 when they displayed at least one measure. This means that the pollutants had affected their mothers to such an extent that they were exposed to this increased risk that remained constant until reaching adolescence, with some showing elevated risk at an earlier age than others.
This higher-risk group of teenagers is more likely to develop Type 2 diabetes, obesity or hypertension in adulthood, the researchers said, although exactly how much higher the group's risk is remains unclear due to study limitations. The team detected statistically significant associations, despite the sample size.
"These chemicals were banned in Spain when this information was collected because they are persistent," Güil noted. However, she added, "They can stay in our body for 20 years, 30 years because they accumulate in fat tissue."
However, the chemicals have been banned in most countries, including most of Europe and the U.S., and a 2001 United Nations convention in Stockholm led to a prohibition on their use and production. Güil cited studies showing the toxicological effect of these chemicals on the human body, with some relating them to cancer.
Yet they remain prevalent today.
"We are still being exposed, and they are still detected in human biomonitoring population studies," Güil explained. She noted that these chemicals are still present in food, particularly in imported food from countries where they are still being used, such as South Africa. Dichlorodiphenyltrichloroethane is used for controlling mosquito transmission of malaria, and the levels of exposure to this chemical are reportedly higher in South African populations.
Another challenge relates to landfills.
"There's a problem with some landfills in some low- and middle-income countries where we can get these chemicals, and they are accumulated in some landfills," Güil said. There is either no control of these chemicals in these landfills whatsoever, "or they just burn them and they are released in the environment," she said.
"But we find them everywhere, even in the arctic areas, in the desert, in the oceans," she continued, "and they stay in the tropic chain within animals, so we find them in soils." The main source of exposure to these chemicals for humans is diet, particularly food from animals because they accumulate in fat tissue.
But there is increasing concern about the effect of these chemicals in the European Union. The Green New Deal for Europe aims to limit the exposure to them, and, "It is trying to find substitutes that are less harmful to humans," Güil said. She stressed that her study "is important in terms of future environmental policies to keep track of these chemicals that are still in all ecosystems and the environment."
Güil is now studying non-persistent organic pollutants like parabens, which are found in personal care products.
The study, "Prenatal exposure to persistent organic pollutants and markers of obesity and cardiometabolic risk in Spanish adolescents," published March 9 in Environment International, was authored by Nuria Güil-Oumrait, Raquel Garcia-Esteban, Monica Guxens, Jordi Sunyer, Maribel Casas and Martine Vrijheid, Barcelona Institute for Global Health; Damaskini Valvic, Icahn School of Medicine at Mount Sinai; and Maties Torrent, Ib-Salut.