Black children with high levels of hormone-altering chemicals used in some shampoos and lotions are more likely to be obese, according to research published today.
The study by New York University scientists is the second to link phthalates to obesity in children but the first to use a large sample of children and look for racial disparities.
Black children have much higher levels of the chemicals in their bodies than children of other races, and for every tripling of certain compounds, they were 22 percent more likely to be obese, according to data from 2,884 children aged 6 to 19. No links to obesity were found in white or Hispanic children.
"The takeaway is we need to consider environmental exposures when looking at the obesity problem," said Leonardo Trasande, a professor at New York University School of Medicine and lead author of the study. "Environmental chemicals may contribute independently of diet and exercise."
Phthalates are a large family of chemicals with varied uses. The phthalates associated with black children's obesity were the kind commonly added to personal care products to make fragrances last longer. Other phthalates are used to make vinyl and can be found in food packaging, medical devices and flooring.
Trasande and colleagues checked for a variety of phthalates and only found a link to the kinds used in personal care products.
Both Trasande and other researchers were quick to point out that this doesn't mean phthalates cause obesity.
"It's a big study and nationally representative, which is good," said Joe Braun, an epidemiology professor at Brown University who was not involved with the research. "But since they measure phthalates levels in urine and obesity at the same time, it's a chicken and egg problem. Do phthalates cause obesity or are obese children more exposed?" It's unclear, he said, when they were exposed relative to when they became obese.
Kathryn St. John, a senior director of product communications at The American Chemistry Council, which represents chemical manufacturers, said no conclusions can be drawn from this study about whether a significant increase in childhood obesity can be linked to phthalate exposure.
"Attempts to link our national obesity problem to minute exposures to chemicals found in common, everyday products are a distraction from efforts to address this important national health issue," St. John said.
Previous studies have linked phthalates to hormone disruption—including hormones responsible for fat tissue and development of the brain and reproductive system. Trasande said it's plausible—though not proven by this study—that phthalates could contribute to obesity by messing with receptors that metabolize lipids and carbohydrates.
One previous study linked phthalates to obesity in children. High phthalate concentrations were associated with increased body mass and waist size in Hispanic and black children aged 6 to 8 in New York City. Phthalates also were linked to adult obesity in a 2007 study.
In the new study, it is unclear why there was only a link for black children, but it could be due to their higher concentrations of the chemicals. For the personal care product-type phthalates, black children had levels 81 percent higher than white children, 45 percent higher than Mexican American children and 4 percent higher than other Hispanic children.
"One possibility is that different racial/ethnic groups use phthalate-containing shampoos and lotions differently, or use products containing different [phthalate] mixes," says the study, which was published online in the journal Environmental Health Perspectives.
Researchers didn't see any differences by age groups. And, while the black children had higher levels of phthalates as a whole, the association with obesity happened at relatively low levels of exposure, Trasande said. The study used data from the U.S. Centers for Disease Control and Prevention's 2008 nationwide testing of chemicals in people's bodies.
It's possible black children are simply more exposed, or they metabolize the chemicals differently, said Emily Barrett, a professor at the University of Rochester who studies exposure to environmental chemicals.
Many factors—including nutrition and stress—could alter how different children metabolize chemicals, said Jennifer Adibi, an epidemiology professor at the University of California, San Francisco.
In a study released late last year by Trasande and colleagues, another hormone disrupting chemical—bisphenol A—was linked to obesity in only white children.
Trasande controlled for diet, television watching, gender and age in the phthalate study. Pinning chemicals to weight gain is a challenge, but the study forces some new thinking about obesity, he said.
The next research step is to look at phthalate exposures from fetus to childhood to try to tease out whether the chemicals are contributing to obesity, he said.
Adibi said the findings are "interesting and scary." While it's not enough evidence to spur policy changes, she hopes it will reframe the conversations about risks to disadvantaged communities.
"This is another reason to increase awareness among low income, African American and Hispanic populations and let them know they're at an increased risk of exposure to these chemicals and that we're seeing these associations (with obesity)," Adibi said.