A link between obesity and exposure to chemicals found in some plastics has been documented in several recent animal studies, including one released Jan. 15 by the University of

California, Irvine.

The studies, most performed on mice, examined the effect of obesogens—chemicals in the environment that are foreign to the body that can affect how it metabolizes fat—as well as other chemicals that disrupt the endocrine system, which regulates the body’s hormones. This disruption interferes with the body’s ability to develop normally.

UCI researchers exposed one generation of mice to tributyltin, an obesogen, also called TBT, through drinking water. Researchers then studied the impact on the three subsequent generations.Bruce Blumberg, professor of pharmaceutical sciences at UCI and a researcher on the TBT study, said the biggest discovery was the transgenerational effects of TBT on obesity, meaning the increased fat accumulation is passed down to subsequent generations without direct exposure.

“The implication is that what we expose ourselves to doesn’t just concern us,” Blumberg said. “What you’re exposed to not only affects your health but also your child’s health and, potentially, your grandchildren and great grandchildren.”

TBT is found in vinyl and is commonly used as an additive in boat hull paint. Michael Skinner, a biological science professor at Washington State University, conducted studies on the industrial plastic chemical Bisphenol A, commonly known as BPA, and some phthalates. Phthalates are plasticizers found in PVC, detergents and children’s toys, and have been known to disrupt the endocrine system.

Skinner conducted studies on mice by exposing them to these chemicals and discovered that generations succeeding the first exposed generation were at an increased risk for obesity.

Exposure to endocrine disrupters, such as TBT, could lead to health problems including ovarian disease, obesity and abnormalities during puberty, said Rob Lustig, a professor of clinical sciences at the University of San Fransisco, in an email. Lustig has conducted several studies on these chemicals.

In Blumberg’s TBT study, the later generations of mice also had greater fat accumulation but no TBT in their system. Blumberg said this implies that TBT’s effects could be permanent.

Though there is little human data to support these findings, Blumberg said there is reason to believe the conclusions are translatable to humans because they affect the same part of the body. TBT activates a hormone receptor called the PPAR gamma, a type of protein that helps regulate the body’s fatty acids and metabolism, which behaves exactly the same way in humans as it does in mice, Blumberg said.

“There’s correlation, but not causation data,” Lustig said, meaning there is a definite pattern between endocrine disruptors and obesity, but a direct link has not been found.

Another issue surrounding these endocrine-disrupting chemicals, according to Blumberg, is that harmful chemicals in paint, plastic and other household products can seep into the environment. He found that TBT is often present in household dust. Lustig, who conducted his own studies on the obesogen fructose, said the chemicals that enter the environment can stay there forever.

The standard of chemical regulation prevents the ban of these chemicals, Blumberg said. To get a chemical off the market, a scientific study is required to show beyond the shadow of a doubt that it is harmful, a difficult and expensive process, he said.

Both Skinner and Blumberg recommend that pregnant women and young children avoid these chemicals by limiting their use of plastic products, pesticides and cosmetics that contain phthalates. Skinner said effects are greater for fetuses and children because the developmental stage is when endocrine is the most important. It’s also the most vulnerable because it programs bodily development.

Blumberg said few human studies are being conducted on this issue. The process of isolating many endocrine-disrupting chemicals is expensive, and the fact that chemicals are not found in the body after one generation of exposure means more research and funding must be conducted before a human study is feasible, he said.

“We wish someone would monitor levels of TBT and all the chemicals we’re interested in because I want to know [what else they do],” Blumberg said, adding that the TBT study provided a lot of new information but has some

serious implications.

“I’m happy for the sake of science, but I’m unhappy for the sake of people,” Blumberg said.