Is there a connection between in utero chemical exposure and obesity?

Some common chemicals ingested during pregnancy could be associated with obesity in offspring, according to a new study.

Dr. Joseph Braun, assistant professor of epidemiology at Brown University, conducted an observational study that found that some children born in the Cincinnati area downstream from an industrial dumping site have more fat as young children if their mothers had high levels of the chemical perfluorooctanoic acid in their blood during pregnancy.

Scientists cannot purposely expose people to toxic chemicals, but inadvertent chemical exposures from dumping can provide epidemiologists with unique opportunities to investigate the possible effects chemicals and other products can have on human health.

In this case, the chemical dump site and the people who lived downstream on the Ohio River presented Braun with such an opportunity.

A DuPont plant in Parkersburg, West Virginia, had been manufacturing fluoro polymers. They're used in industrial processes as a surfactant, stain and water repellant and in some food packaging. They are also used in firefighting foams.

The manufacturing process for these chemicals uses perfluorooctanoic acid, or PFOA. Until 2000, DuPont was releasing PFOA into the environment.

As is often the case in observational studies, Braun can’t be certain that this is how the women in the study were exposed to the chemical. He can only infer based on the available evidence.

“We suspect that the vast majority of exposure to these chemicals [actually] comes from the diet,” Braun explains. "[But] we speculated that the elevated levels of perfluorooctanoic acid in these women could be related to the ingestion of contaminated drinking water. However, we were not able to show that in this study, and this is something we're trying to look at in our future work.”

PFOA is in a class of chemicals scientists have labelled obesogens. Scientists speculate that exposure to these chemicals may increase the risk of obesity or other diseases related to obesity, like diabetes or cardiovascular disease.

“Obesogens may work by affecting hormonal systems that are involved in programming fetal growth, or growth in the [born] child,” Braun says. “They may also affect the programming of our appetite or metabolism. Or they could affect how our genes are expressed.”

In the study, Braun and his colleagues measured the concentration of several perfluoroalkyl substances in the blood of pregnant women, including perfluorooctanoic acid. Then they looked at the relationship between levels of these chemicals in the women's blood during pregnancy and their children's adiposity at age eight. Adiposity is the polite, scientific term for fat.

Braun took measurements of body mass index, waist circumference and an estimate of total body fat percentage. He found that, compared to children born to women in the lowest third of exposure to PFOA, the children born to women with higher concentrations of PFOA had .9 to 2.4 pounds more body fat at eight years of age.

“We worry about this for a couple of reasons,” Braun says. “One is that any increase in body fat is bad because it's very difficult to lose fat once you gain it. We can get children to lose weight, but it's difficult to get them to sustain that weight loss, and the decreases in weight aren't as big as we'd like.

“In addition,” he continues, “increases in body fat — any increase, even these small amounts — can be associated with later life risk of disease like some cancers, cardiovascular disease and diabetes.”

Levels of PFOA have been dropping for the past few years, because they are voluntarily being phased out of commerce by the manufacturers that use and make them. They are still detectable in over 90 percent of people in the US, however.

This concerns Braun and other scientists because they have long half-lives in the environment and they have a long half-life — years or more — in the human body.

“We don't know for certain that PFOA or this class of perfluoroalkyl substances is responsible for the obesity epidemic,” Braun says. “Nor do we know if the broader class of chemical obesogens is responsible for the epidemic. However, we do know that some chemical exposures, some of which we suspect are obesogens, could increase an individual's risk for obesity or increase their body fat.”

“So we have only begun unpacking these associations between obesity and genetics, environment and other factors that we think contribute to obesity, like diet or lack of exercise,” Braun concludes.

This article is based on an interview that aired on PRI's Living on Earth with Steve Curwood