By Janet Raloff
A new rodent study finds that even low-dose exposures to bisphenol A — a hormone-mimicking chemical that leaches out of many plastics and food-can liners — can provoke changes during pregnancy that are bad for both moms and their male offspring.
The new data indicate that BPA is a “possible risk factor for gestational diabetes, type 2 diabetes and even cardiovascular disease associated with metabolic syndrome,” authors of the report say. Metabolic syndrome, which may affect up to one-third of adults, consists of a constellation of prediabetic symptoms that can include elevated blood pressure, higher levels of harmful LDL cholesterol and increases in the length of time fats circulate in the blood (SN: 4/8/00, p. 236).
In mice, the new study reports, exposure to BPA during mid- through late pregnancy impaired blood-glucose regulation. The change probably wouldn’t be considered outright gestational diabetes, but it was certainly significant enough to suggest risk for the condition, explains study leader Angel Nadal of Miguel Hernández University in Elche, Spain. The biggest effect, he notes, came from an amount of BPA equal to just one-fifth the dose currently estimated by the U.S. Environmental Protection Agency as being safe for humans.
Four months after giving birth, BPA-exposed mother mice had become 6 percent heavier than unexposed moms, despite eating the same amount of chow. This suggested that metabolism was slowed in the exposed mice. They also had higher levels of fats known as triglycerides circulating in their blood than did the untreated moms. But, still, researchers found no clear-cut disease. The findings were reported May 19 online, ahead of print, in Environmental Health Perspectives.
A dose of 100 micrograms of BPA daily per kilogram of body weight, which is twice EPA’s ostensibly safe limit for humans, also elicited insulin resistance and other blood-sugar–regulation problems during pregnancy. But when these animals were later administered a big dose of glucose and then monitored for evidence of diabetes-like changes, moms with the higher BPA exposures actually performed better than did those mice that had gotten just 10 µg/kg per day, for reasons that remain unclear. Signs of any prediabetic symptoms resolved immediately after pregnancy, but then reemerged four months later.
These data challenge the long-standing assumption that effects of exposure to hormone-mimicking contaminants during adulthood “are reversible” after exposure ceases, Nadal and his colleagues conclude.
Male offspring whose exposures to BPA occurred only in the womb were born healthy, but developed prediabetic changes by the time they were six months old. In human terms, that equates to about age 35.
These findings “are huge,” says Cheryl Watson of the University of Texas Medical Branch in Galveston. “It means we need to start paying attention to BPA exposures in pregnant women.” Not only do they face risks, she says, but the changes that occur during a critical window in fetal development may set the stage for adult disease in their children.
Nadal agrees. Toxicologists have long assumed that because BPA can cross the placenta, any effect of this contaminant comes from direct exposure to the baby. “But what we are showing is that BPA also affects the mother,” he says. “This means we can’t really separate whether effects in the offspring are due to BPA or to the metabolic changes that occur in the moms during pregnancy.”
Earlier studies by Nadal’s group (SN: 1/21/06, p. 36) and others have picked up hints that BPA might trigger diabetes and at least one survey of the U.S. population (SN: 10/11/08, p. 14) found an elevated incidence of diabetes among people with the highest concentrations of the contaminant in their blood. But this is the first to identify blood sugar changes in pregnancy and after, much less a link between such changes and an apparent increased vulnerability to diabetes in the offspring.
One potential limitation endocrinologist Nira Ben-Jonathan of the University of Cincinnati, raised about the study was how the BPA was administered. Moms were injected with it, not given BPA-laced food. Injections bypass the gastrointestinal tract, Ben-Jonathan notes, which might otherwise have broken down some BPA before it could be absorbed.
