Better Keep Plastic Out of the Microwave

It might be easier to just microwave leftovers in the plastic container you left them in, but new studies suggest you might want to invest the time to wash an extra dish. Zapping a burrito in a plastic wrapper, or storing food in plastic containers that have been washed in the dishwasher, could increase the likelihood that you’ll ingest phthalates, a group of chemicals used in some plastics.

Phthalates are often used in consumer products like soaps, cosmetics, plastic pipes, and shower curtains, among others. While the National Institutes of Health says that “the human health effects of phthalates are not yet fully known,” they are thought to be endocrine disruptors, meaning they could interfere with the body’s glands, metabolism, reproduction, and other functions of the endocrine system. Exposure to some phthalates has also been linked to preterm birth and neurobehavioral problems in infants exposed in the womb. According to the Centers for Disease Control and Prevention, phthalate exposure is widespread in the U.S. population.

A 2014 report by the U.S. Consumer Product Safety Commission found that “food, beverages, and drugs via direct ingestion…constituted the highest phthalate exposures to all subpopulations” in the United States. Phthalates can easily leach from plastic into food, so some kinds of plastic food packaging or even plastics used in food processing at factories could increase the risk of the chemicals being ingested.

Now, a pair of recent studies by researchers at the New York University School of Medicine have found some additional associations between phthalate levels in urine and troubling health outcomes in children. One, published Wednesday in the journal Hypertension, found a link between three kinds of phthalates and higher blood pressure. Another, published in Endocrine Society in May, linked two of those phthalates to increased insulin resistance, a characteristic of diabetes (if high enough).

“There has been some increasing attention to one particular phthalate called DEHP that’s been used until recently in food wraps and other food contact surfaces. [DEHP is] increasingly being replaced by two chemicals called DIDP and DINP,” says Leonardo Trasande, the lead study author and a professor in the department of pediatrics at NYU.

The first study linked higher blood pressure to DEHP—“of particular interest because industrial processes to produce food frequently use plastic products containing DEHP,” the study reads—as well as DINP and DIDP. The second found a connection between insulin resistance and DEHP and DINP.

In both of these studies, the effects persisted even after controlling for socioeconomic and other demographic factors, and for things like diet and physical activity, which are also obviously big factors in the complex interplay between obesity, blood pressure, and insulin resistance.

“Clearly, diet and physical activity are the major contributors to metabolic disorders in children and adolescents but increasingly evidence suggests that chemicals [are] a potential third contributor to the epidemic,” Trasande says. “In contrast to diet and physical activity, which can be hard to modify, exposures to chemicals can be actively regulated and managed.”

For people wanting to stay on the safe side, Trasande suggests not putting plastic food containers in the microwave or the dishwasher, which can increase leaching from the plastic into food; not drinking from plastic containers with the recycling numbers 3 (for polyvinyl chloride), 6 (for polystyrene), or 7 (for, uh, whatever else doesn’t have its own number), “which indicate they’re manufactured with chemicals of concern,” he says. And when plastic containers get scratched up, maybe just throw them away—that could mean the protective coating has broken down.

These are some of the first studies looking at the potential effects of DIDP and DINP. The CDC’s factsheet on the chemicals still says, “More research is needed to assess the human health effects of exposure to phthalates.”

“Yet the current regulatory structure in the United States assumes the chemicals are innocent until proven guilty,” Trasande says. “I’m certainly not suggesting we move back to an 1890s lifestyle. Clearly there are many chemicals that do not pose problems to daily living, but insofar as chemicals can be regulated, there's an opportunity to reduce disease and disability that can be traced back to these chemicals.”