Could plastic bottles and metal food-can liners be contributing to the American asthma epidemic? A study presented at the Pediatric Academic Societies meeting this past weekend suggests so, finding that pregnant women exposed to bisphenol A (BPA)—a chemical building block of plastics from polycarbonate to polyester—gave birth to children with a higher risk of respiratory problems. That finding seems to confirm earlier studies that found such a link in mice—and BPA exposure at low levels during pregnancy has already been linked to future health problems, such as cancer, in children.

BPA is present in more than 90 percent of Americans young and old, according to the U.S. Centers for Disease Control and Prevention, although at levels below those considered unsafe by government regulators. But the new study adds yet more cause for concern surrounding BPA.

As a result of a growing body of scientific studies, various countries have begun to investigate the plastic building block. Canada has classified it as a toxic substance and banned it from baby bottles while the European Union has placed it on a list of "Substances of Very High Concern," due to its capacity to mimic the human hormone estrogen, where it is joined by other substances, such as plastic softeners phthalates, boric acid and lead chromate. The U.S. Food and Drug Administration, for its part, still holds that BPA has not been proven to cause harm but nevertheless recommends avoiding plastic baby bottles and the U.S. Environmental Protection Agency calls BPA a "chemical of concern," which could ultimately lead to regulation of the substance in future.

Endocrine disruptors such as BPA are chemicals that bond to the same receptors as natural hormones, in the case of BPA: estrogen. Potential effects include developmental issues, obesity, heart disease, diabetes and cancer. Most troublingly, such chemicals appear to work in concert and may prove even more harmful at low doses than high.

In this latest study, researchers followed 367 mothers and their infants, taking urine samples 16 and 26 weeks into the pregnancy to measure BPA levels. Almost all the babies—99 percent—were born to mothers who had detectable levels of BPA in their urine at either or both of these points.

Then the mothers were asked every six months for three years whether their child wheezed. At 6 months of age, women with the highest levels of BPA in their urine had babies more likely to wheeze—though those differences disappeared by the time the children were three years old. BPA levels at 16 weeks into the pregnancy seemed more important in determining future infant wheezing than those later in the term.

Of course, correlation is not causation and there are plenty of other risk factors for asthma, such as the particulate matter spewing from car and truck tailpipes or pollen allergies. Perhaps as a result, Coca-Cola shareholders voted last week to continue using BPA-based epoxy resin in its can linings, the position advocated by the beverage company's executives.

For that reason, among others, it remains difficult to avoid BPA and its fellow chemicals of concern. After all, BPA is also in products ranging from toys to cash register receipts. Nevertheless, the FDA, EPA and others continue to investigate the potential effects of a chemical that's been in use for more than 40 years.