Obesity's Hidden Trigger
by Emily Main
The Green Guide
July/August 2007 Issue
If you've ever suspected that there's a reason you can't burn off those last five pounds, you may be on to something. Recent studies on certain hormone-disrupting and environmentally persistent compounds are leading researchers to believe there's a plausible link between these ubiquitous chemicals and our ever-expanding waistlines.
The World Health Organization estimates that 1 billion of the world's nearly 7 billion citizens are overweight, 300 million of whom are defined as clinically obese. "People want to blame 40-ounce Cokes--and that's important--but there's reason to believe there are other things in play," says Richard Stahlhut, M.D., M.P.H., preventive medicine resident at the University of Rochester Medical Center.
Stahlhut and his colleagues wondered if a group of hormone-disrupting chemicals called phthalates (pronounced "thay-lates"), found in a wide array of everyday products, might be adding to this epidemic. Analyzing data from the Centers for Disease Control and Prevention's most recent National Health and Nutrition Examination Survey, Stahlhut and his colleagues compared six phthalate metabolites (phthalates processed by the body) found in men's urine samples to their corresponding waist circumferences. Two of the phthalates targeted were DEHP, used in synthetic fragrances and polyvinyl chloride (PVC) products (i.e. floor tiles, shower curtains and hospital IV bags), as well as DBP, used in nail polishes, floor finishes and paints.
The results, published online last March in Environmental Health Perspectives (EHP), revealed that American men with abdominal obesity or insulin resistance (a precursor to diabetes) were more likely to have high levels of the metabolites in their urine than men without those problems. Stahlhut is quick to point out that there's no definitive link proving that excessive phthalate exposure causes obesity, but the study does suggest a possible connection. "[These results are] what you would expect if phthalates are lowering testosterone levels," Stahlhut says, and "low testosterone in adult men, from whatever cause, is known to cause abdominal obesity and insulin resistance." Past research has demonstrated the effects of phthalates on testosterone; a 2006 Danish study of infant boys found that those exposed to phthalates via breast milk had lower testosterone levels and abnormal reproductive development.
Fredrick vom Saal, Ph.D., a developmental biologist at the University of Missouri, is currently studying the obesity-inducing effects on pregnant mice of BPA, a hormone-disrupting chemical found in #7 polycarbonate bottles, dental sealants and can linings. Presenting preliminary results at the American Association for the Advancement of Science's annual meeting last February, he discovered that these mice, which had been fed very low doses of BPA, had offspring that exhibited abnormal growth later in life. While it's not clear that BPA is linked to obesity, says vom Saal, "we do know that it makes animals bigger. It doesn't categorize them as obese, but obesity is a very particular aspect of growth."
In yet another study in press online at Environmental Science & Technology, researchers from the Johns Hopkins Bloomberg School of Public Health tested cord blood taken from newborns for ten environmentally persistent perfluorochemicals (PFCs), including perfluorooctanoic acid (PFOA), used in the manufacture of non-stick pans and in microwave popcorn bags, and the now-banned perfluorooctanoic sulfonate (PFOS). High levels of both were associated with low birth weight, itself a risk factor for obesity later in life. "We do know, in the case of animals, that some of these chemicals have effects later in life," says Lynn Goldman, M.D., one of the study's lead authors.
While all these links are preliminary, the studies point to "where folks need to focus effort," says Stahlhut. "There's some exposure or combination of exposures that everybody thinks is okay but isn't."
Fortunately, awareness is being raised. In California, a ban on phthalates in children's toys reached the senate floor before defeat and Maine's legislature is considering a bill that would bar the sale of any children's product containing BPA or phthalates. Until such legislation reaches your state, "People have to protect themselves," says Stahlhut. Vom Saal's research points out that BPA is harmful even before children are born, so such laws may not offer the highest level of protection. "This is a very, very complex problem, and it will take many years to get to the bottom of it," Stahlhut adds. "The organic approach--avoiding complex chemicals you don't really need, and otherwise being 'zen' about it--may be a reasonable strategy."
The Green Guide
July/August 2007 Issue
If you've ever suspected that there's a reason you can't burn off those last five pounds, you may be on to something. Recent studies on certain hormone-disrupting and environmentally persistent compounds are leading researchers to believe there's a plausible link between these ubiquitous chemicals and our ever-expanding waistlines.
The World Health Organization estimates that 1 billion of the world's nearly 7 billion citizens are overweight, 300 million of whom are defined as clinically obese. "People want to blame 40-ounce Cokes--and that's important--but there's reason to believe there are other things in play," says Richard Stahlhut, M.D., M.P.H., preventive medicine resident at the University of Rochester Medical Center.
Stahlhut and his colleagues wondered if a group of hormone-disrupting chemicals called phthalates (pronounced "thay-lates"), found in a wide array of everyday products, might be adding to this epidemic. Analyzing data from the Centers for Disease Control and Prevention's most recent National Health and Nutrition Examination Survey, Stahlhut and his colleagues compared six phthalate metabolites (phthalates processed by the body) found in men's urine samples to their corresponding waist circumferences. Two of the phthalates targeted were DEHP, used in synthetic fragrances and polyvinyl chloride (PVC) products (i.e. floor tiles, shower curtains and hospital IV bags), as well as DBP, used in nail polishes, floor finishes and paints.
The results, published online last March in Environmental Health Perspectives (EHP), revealed that American men with abdominal obesity or insulin resistance (a precursor to diabetes) were more likely to have high levels of the metabolites in their urine than men without those problems. Stahlhut is quick to point out that there's no definitive link proving that excessive phthalate exposure causes obesity, but the study does suggest a possible connection. "[These results are] what you would expect if phthalates are lowering testosterone levels," Stahlhut says, and "low testosterone in adult men, from whatever cause, is known to cause abdominal obesity and insulin resistance." Past research has demonstrated the effects of phthalates on testosterone; a 2006 Danish study of infant boys found that those exposed to phthalates via breast milk had lower testosterone levels and abnormal reproductive development.
Fredrick vom Saal, Ph.D., a developmental biologist at the University of Missouri, is currently studying the obesity-inducing effects on pregnant mice of BPA, a hormone-disrupting chemical found in #7 polycarbonate bottles, dental sealants and can linings. Presenting preliminary results at the American Association for the Advancement of Science's annual meeting last February, he discovered that these mice, which had been fed very low doses of BPA, had offspring that exhibited abnormal growth later in life. While it's not clear that BPA is linked to obesity, says vom Saal, "we do know that it makes animals bigger. It doesn't categorize them as obese, but obesity is a very particular aspect of growth."
In yet another study in press online at Environmental Science & Technology, researchers from the Johns Hopkins Bloomberg School of Public Health tested cord blood taken from newborns for ten environmentally persistent perfluorochemicals (PFCs), including perfluorooctanoic acid (PFOA), used in the manufacture of non-stick pans and in microwave popcorn bags, and the now-banned perfluorooctanoic sulfonate (PFOS). High levels of both were associated with low birth weight, itself a risk factor for obesity later in life. "We do know, in the case of animals, that some of these chemicals have effects later in life," says Lynn Goldman, M.D., one of the study's lead authors.
While all these links are preliminary, the studies point to "where folks need to focus effort," says Stahlhut. "There's some exposure or combination of exposures that everybody thinks is okay but isn't."
Fortunately, awareness is being raised. In California, a ban on phthalates in children's toys reached the senate floor before defeat and Maine's legislature is considering a bill that would bar the sale of any children's product containing BPA or phthalates. Until such legislation reaches your state, "People have to protect themselves," says Stahlhut. Vom Saal's research points out that BPA is harmful even before children are born, so such laws may not offer the highest level of protection. "This is a very, very complex problem, and it will take many years to get to the bottom of it," Stahlhut adds. "The organic approach--avoiding complex chemicals you don't really need, and otherwise being 'zen' about it--may be a reasonable strategy."
What You Can Do
* Exercise regularly.
* Eat less fat. PFOA and PFOS don't build up in fat, says Goldman, but many PFCs do. "As a general precaution, eating less fat and less animal fat is a good idea," she advises.
* Purchase cookware without non-stick features, and avoid microwave popcorn: PFOA released from bags accounts for over 20 percent of the chemical measured in Americans' blood.
* Choose phthalate-free products: See Moisturizers and Flooring product reports (www.thegreenguide.com/reports) and www.greenerpenny.com. When pregnant, ask ahead about your hospital's policy on PVC in medical devices.
* See the Baby Bottle and Plastic Containers product reports for non-polycarbonate bottles at www.thegreenguide.com/reports.
* Avoid canned products that may be packaged in cans lined with BPA. See "The Bisphenol-A Debate: A Suspect Chemical in Plastic Bottles and Cans," and "A Survey of Bisphenol-A in U.S. Canned Foods".
© 2007 National Geographic Society
posted by Swallowtail at 17:57
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