Exposure to hazardous chemicals in the womb may be linked to rapid childhood weight gain, study finds

Babies exposed to a set of common chemicals while in the womb may be at higher risk of gaining weight rapidly during early childhood, a recent study suggests.

The research, published last week in the journal Environmental Health Perspectives, identified a link between exposure to endocrine-disrupting chemicals in utero and a rapid increase in a child’s body mass index from birth to 9 years of age.

The category of chemicals studied includes per- and polyfluoroalkyl substances — better known as PFAS or “forever chemicals” because of how slowly they degrade — as well as some compounds used in or derived from fungicides and pesticides. Such chemicals can be found in everyday items including nonstick cookware, cosmetic products and plastic food containers, as well as in some meat and fish if the animals were exposed to contaminated land or water. They are thought to interact with humans’ endocrine systems by mimicking natural hormones.

The new findings are based on data from more than 1,900 pairs of mothers and children in Spain, gathered from 2003 to 2008. The women, whose racial breakdown was not described, gave blood and urine samples during pregnancy, from which the researchers measured the concentration of endocrine-disrupting chemicals in their bodies. Then the scientists measured their children’s BMIs at several points up to age 9. (BMI is a measure of body fat based on one’s height and weight, though the metric is not necessarily a good indicator of individual health.)

The results of the analysis showed that babies with more exposure to endocrine-disrupting chemicals before birth were more likely to be born smaller than the study group’s average, then experience rapid growth during their early years of life. Exposure to two chemicals in particular was also associated with a higher risk of rapid BMI gain after a baby was born larger than average.

A possible reason for this correlation, according to the study’s lead author, Parisa Montazeri, is that endocrine-disrupting chemicals can mimic or block hormones involved in the process of breaking down food for energy, which can in turn alter the body’s hunger cues or sensitivity to sugar and fats.

“This is what can cause some of those weight issues,” she said.

Montazeri, who works as a scientific coordinator at the Barcelona Institute for Global Health, said a rapid increase in BMI during childhood is linked to health issues into adulthood, including obesity, fatty liver disease, cardiovascular disease and diabetes. So pinpointing early factors that can contribute to those health issues may better enable doctors to intervene to mitigate the risk of disease later in life.

“It also contributes to explaining a piece of the puzzle as to why obesity is on the rise,” Montazeri said, though she noted that endocrine-disrupting chemicals are just “one aspect that helps explain this phenomenon, along with the typical sedentary lifestyle and eating.”

She said the most concerning chemicals are those that don’t degrade for decades, such as PFAS — found in stain- or water-resistant products — and polychlorinated biphenyls, which are used as lubricants in electrical equipment and in some oil-based paints and floor finishes.

Other endocrine disruptors, such as phthalates and parabens, don’t stay in the body much longer than a day, Montazeri said, but people can be regularly exposed through personal care products such as shampoo and hair spray.

Exposure to chemicals during pregnancy is particularly concerning, several experts said, because a fetus’ organs are still forming.

The exposure can therefore “have a larger effect on a baby or a person developing at this time than they would at other points in your life,” said Dr. Brigid Gregg, an assistant professor of pediatric endocrinology at the University of Michigan who wasn’t involved in the new study.

Past research has similarly found a link between endocrine-disrupting chemicals and weight gain in childhood. A June study found that exposure to PFAS in the womb was slightly associated with a risk of obesity in children and adolescents, and research published in 2021 found that exposure to a type of pesticide in utero was linked to a higher risk of infants becoming overweight. A 2020 study, meanwhile, found that prenatal exposure to phthalates and bisphenols — another endocrine-disrupting chemical found in plastic items like water bottles — was linked to increased fat around the heart in children.

However, most studies on the topic so far have looked at the health effects of just one or two types of chemicals, according to Dr. Leonardo Trasande, a pediatrics professor at New York University. The new study examines how a broader combination can affect childhood development, he said.

“We’re not exposed to one chemical at a time,” said Trasande, who wasn’t involved in the research. “We’re probably exposed to tens of thousands, at least, of chemicals at any given time, of which a smaller subset are probably the most problematic.”

Can pregnant women reduce their exposure?

Montazeri said pregnant women can make adjustments to limit exposure to endocrine-disrupting chemicals.

A mother of two herself, Montazeri said that when she was pregnant, she avoided storing food in plastic containers and did not heat plastic in the microwave. She also cooked with stainless steel pans or cast-iron skillets instead of nonstick pans, which can contain PFAS. And she avoided eating large fish such as swordfish or tuna, which can contain higher concentrations of mercury and chemicals.

She further suggested that pregnant women eat organic food when possible, since that limits pesticide exposure, and check for parabens and phthalates on the ingredient labels of personal care products such as lotion or nail polish.

In the long run, Trasande said, he hopes to see the United States enact new regulations that reduce people’s exposure to endocrine-disrupting chemicals.

“We’ve been unwitting participants in an unnatural experiment,” he said. “And so the implications are very clear that we need to be more proactive about reducing exposures to these chemicals.”