(CNN) — Children exposed to higher levels of pesticides, fungicides and synthetic chemicals while in the womb are more likely to have a higher body mass index during childhood than those exposed to lower levels of such chemicals, a new study found.
“This is important knowledge given that accelerated growth during childhood has been linked to various health issues during childhood and in later life, including obesity, cardiovascular diseases, and diabetes,” said first author Parisa Montazeri, an epidemiologist and scientific coordinator at the Barcelona Institute for Global Health in Spain, in an email.
All the chemicals examined in the study are suspected “obesogens” — chemicals that may promote obesity by interfering with metabolism and hormones, Montazeri said.
“All children were exposed prenatally,” she added. “Some measurements were below the limit of detection, meaning the sample had too low a concentration of the chemical being measured to register, but this was the minority of cases.”
Earlier studies have shown links between such chemicals and BMI and growth in children as well as higher BMIs and levels of obesity in adults.
“This (study) reinforces the reality that synthetic chemicals do make us fatter,” said Dr. Leonardo Trasande, director of environmental pediatrics at NYU Langone Health, in an email. He was not involved in the study.
The study measured levels of 23 common contaminants in the blood and urine of 1,911 expectant moms taking part in the birth cohort of a longitudinal study conducted in Spain by the INfancia y Medio Ambiente Project. The research network aims to examine the lifetime impact of exposure in the womb to chemical contaminants in air, water and food.
The new study, published Wednesday in the journal Environmental Health Perspectives, followed the children’s growth and development at 6 months and again at 1, 2, 4, 7 and 9 years of age.
A number of the chemicals in the study are considered “persistent” because they are slow to break down, Montazeri said: “They stay in the environment and our bodies for a long time, from years to decades.”
The fungicide hexachlorobenzene, or HCB, is one such chemical. It was banned in the United States in 1984, but “may be created as either a by-product or an impurity in the manufacturing process for certain chemicals and pesticides,” according to the US Centers for Disease Control and Prevention.
“HCB is well absorbed after oral administration, distributes widely throughout the body, and accumulates in fatty tissues where it persists for years,” the CDC noted.
Researchers also measured levels of the pesticide dichlorodiphenyldichloroethylene, or DDE, which occurs when DDT, a pesticide banned in the US in 1972, breaks down in the environment.
“Microorganisms in the soil slowly break down DDT (it can take anywhere from 2 to 15 years to break down half of the DDT),” according to the CDC.
Both DDT and HCB contamination in people occurs “mainly through bioaccumulation in the food chain via fish, fish products, meat (and) dairy products,” Montazeri said.
The study also measured levels of polychlorinated biphenyls, or PCBs, that were banned in the US in 1979 after they were shown to cause cancer in people and a host of other health issues in animals. However, a loophole in the regulations allows some PCBs to be manufactured in certain situations, according to the US Environmental Protection Agency.
Levels of perfluoroalkyl and polyfluoroalkyl substances, or PFAS, were also examined. Known as “forever chemicals” because they can take decades to break down, PFAS have been in use since the 1950s to make products that resist heat, oil, grease, stains and water. A February study found PFAS altered thyroid function in children, while a 300-page report by the National Academies of Sciences, Engineering and Medicine found “sufficient” scientific evidence of an association between PFAS exposure and an increased risk of adult kidney cancer and abnormally high cholesterol levels.
The July 2022 report also found PFAS exposure was sufficiently associated with decreased infant and fetal growth as well as decreased antibody response to vaccines in both adults and children.
Other chemicals in the study, such as phthalates and phenols, are less persistent, living in the body for hours or days before being flushed. Still, a 2021 report found phthalates cause neurodevelopmental harm in fetuses, infants and children. Studies have also linked phthalates to childhood obesity, asthma, cardiovascular issues, cancer and reproductive problems such as genital malformations and undescended testicles in baby boys and low sperm counts and testosterone levels in adult men.
“Phthalates and phenols come from plastics and personal care products,” Montazeri said. “Exposure can come from contaminated food and drink, and exposure via skin contact or even inhalation.”
A more realistic measurement
Researchers measured the chemicals both individually and as a mixture, with the latter offering a more “realistic representation” of how humans are exposed to common contaminants, Montazeri said.
Trasande, who is also a professor of pediatrics and population health at NYU’s Grossman School of Medicine, added, “The study adds to ample literature suggesting that it’s as important to look at mixtures of chemicals because exposures are weight gain by a thousand cuts … and one exposure may make someone more vulnerable for the other.”
Results showed that “persistent” chemicals, such as HCB, DDE, PCBs and one of the PFAS were associated with increased risk of low birth weight, which can delay development, followed by an acceleration in BMI that ranged between 19% and 32%.
“We found this association in both single chemical models and the mixture models,” Montazeri said. “These babies start off smaller, then grow very rapidly, then they continue on this accelerated trajectory so that at the end of our measurements (9 years) they have some of the highest BMIs.”
The study was not able to determine whether children continued to absorb chemicals after birth, via breast milk, food, air, water, soil and household products that contain various contaminants.
“Exposures of the child after the pregnancy may have effects on the child BMI trajectories, but this would not explain the associations we find between exposure in the womb and the BMI trajectories,” Montazeri said. “Our study emphasizes the need for more research to assess the health implications of prenatal environmental chemical exposure over the course of a child’s life.”
How to avoid exposure to possibly toxic chemicals
An expectant mother can take steps to limit exposure to potentially toxic chemicals.
“On an individual level for a pregnant mother, recommendations would be to avoid storing and microwaving food in plastic containers (and to) avoid cooking with non-stick pans,” Montazeri said in an email.
Additional tips from experts include:
• Don’t eat fish known to be high in mercury and PCBs such as shark and swordfish.
• Eat local, organic foods as often as possible to avoid pesticides and other chemicals. For packaged goods, use the Environmental Working Group’s Food Scores database to find foods with fewer additives.
• Check the labels of cosmetics, which often contain phthalates and other chemicals that have been linked to harm in people and animals. Use EWG’s cosmetic database to find options with fewer contaminants.
• Choose ceramic or stainless steel cookware and avoid products with flame retardants.
• Use a wet mop when cleaning floors to remove dust that can contain chemicals.
• Test your water for PFAS and choose a certified filter from the National Sanitation Foundation.
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