The study, published today in the Environmental Health Perspectives journal, is the first to show this link between fetal exposure to bisphenol-A (BPA) and body fat in children at age 7. While there are a number of factors in obesity—genetics, diet, exercise, disease—the study adds to evidence that environmental chemicals may be playing a role in the health crisis costing the U.S. lives and dollars.
Chemicals Impact Body Weight
“For years when we thought of obesity we thought of eating and exercise, but we’re learning that it’s more complicated than that,” said Kim Harley, associate director of the University of California, Berkeley Center for Environmental Research and Children’s Health.
“There are clues that there are chemicals that also impact later body weight,” said Harley, who was not involved in the current study. “BPA is one we’re really concerned about.”
From pregnancy through early childhood, researchers checked the urine and children body sizes of 369 mother-child pairs in New York City. They found that higher exposure to BPA before birth—estimated by looking at the mothers’ third trimester urine—meant the children at age 7 had higher body fat masses and waist sizes.
Researchers did not see an association between body fat and BPA levels in the children themselves at ages three or five. That finding, the scientists said, suggests fetal exposure may be a time of heightened vulnerability to the chemical.
“The prenatal window is a time when there really should be caution exerted for unnecessary exposures,” said lead author Lori Hoepner, an investigator at the Columbia Center for Children’s Environmental Health and assistant professor at SUNY Downstate Medical Center.
Child Obesity Crisis
Health officials for years have been warning about the child obesity crisis in the U.S. An estimated 17 percent of children and teens aged 2 to 19 years old are obese, according to the U.S. Centers for Disease Control and Prevention.
BPA can leach out of can linings and into the food and studies show that just about everyone has traces of the chemical in their body—researchers believe diet is the major exposure route. Ninety-four percent of the women in this study had the chemicals in their urine.
The study doesn’t prove prenatal exposure to the chemical causes obesity, but BPA—used to make plastic hard and shatterproof—mimics the hormone estrogen and acts as an endocrine disruptor. Properly functioning hormones are crucial to reproduction, as well as development, brain function and immune systems. “Our fat is an endocrine organ and hormonally active,” Harley said. “The fat in our body produces hormones, is regulated by hormones, and hormones tell our body how to lay down fat cells, and regulate our hunger and how we mobilize fat,” she said.
Animal studies have found prenatal BPA exposure linked to offspring obesity.
“There are clues that there are chemicals that also impact later body weight. BPA is one we’re really concerned about.”-Kim Harley, University of California, Berkeley “When you dose pregnant rats, BPA is associated with increased fat mass in offspring, even later in life. As the offspring reach adulthood, there’s more fat tissue, heavier body weight, and insulin resistance in rats,” Harley said.
Strong Link Between BPA and Obesity
Other human studies have found a similar link between BPA exposure and signs of child obesity, but have focused on children’s exposure. The few studies looking at prenatal exposure and children’s body mass have been mixed.
“Some will say the human [research] isn’t completely consistent, but with human health science it often never is,” said said Dr. Leonardo Trasande, an associate professor and researcher at the NYU School of Medicine who was not involved in the study. “We have to decide whether we should act based on the evidence before us. The FDA consistently chooses to not act to limit BPA in food uses, despite bans in baby bottles and sippy cups.”
Trasande pointed to the crushing economic impact of obesity. In a series of papers over the past couple years, he and others have been slapping price tags on health issues due to exposures to endocrine disrupting compounds, including BPA, pesticides and phthalates.
In the U.S. alone, Trasande estimated BPA exposure was linked to more than 12,000 cases of childhood obesity in 2008, along with 33,800 cases of new heart disease, another suspected health impact from exposure. The total cost of that additional obesity and heart disease? An estimated $2.98 billion.
“The type of exposure-response relationship we used in those studies is similar to what they found in this study,” he said, adding that BPA replacements, such as bisphenol-S (BPS), are another area of emerging concern as many seem to have the same endocrine disrupting effects.
The American Chemistry Council, which represents chemical manufacturers, has repeatedly defended BPA’s safety. In response to Hoepner’s study, Steve Hentges, a representative from the council, said in an emailed response that “statistical associations are not the same as causation, in spite of cleverly-worded headlines designed to imply otherwise” referring to the study’s press release.
BPA Does Not Break Down Safely In The Body
Industry has long assured the public that BPA breaks down safely in the human body. But last year, in a study of mice, Health Canada researchers reported rather it seems the body transforms it into a compound that might spur obesity.
The exposure-body fat link was a bit stronger in girls than boys in Hoepner’s study, and she said more studies are needed to tease out whether there are different gender vulnerabilities.
Beginning in 1999, researchers have been studying this cohort of mothers and children since the mothers’ third trimester of pregnancy. Hoepner said they would follow the children up to age 18 to see if this effect persists into later childhood and adolescence.
Though the study is not definitive, mothers-to-be should take note, Hoepner said.
“This is one of potentially many exposures, and pregnant women should try to reduce their exposure to BPA,” Hoepner said. “Exposure could be a preventable factor potentially involved in childhood obesity.”