They’re genetically the same, raised in the same lab and given the same food and chance to exercise. Yet the bottom one is svelte, while the other looks like, well, an American.
The only difference is that the top one was exposed at birth to just one part per billion of an endocrine-disrupting chemical. The brief exposure programmed the mouse to put on fat, and although there were no significant differences in caloric intake or expenditure, it continued to put on flab long after the chemical was gone.
That experiment is one of a growing number of peer-reviewed scientific studies suggesting that one factor in the industrialized world’s obesity epidemic (along with Twinkies, soda and television) may be endocrine-disrupting chemicals. These chemicals are largely unregulated — they are in food, couches, machine receipts, shampoos and other personal care products — and a raft of new studies suggest that they can lead to the formation of more and larger fat cells.
Endocrine disruptors are a class of chemicals that mimic hormones and therefore confuse the body. Initially, they provoked concern because of their links to cancers and the malformation of sex organs. Those concerns continue, but the newest area of research is the impact that they have on fat storage.
Bruce Blumberg, a developmental biologist at the University of California, Irvine, coined the term “obesogen” in a 2006 journal article to refer to chemicals that cause animals to store fat. Initially, this concept was highly controversial among obesity experts, but a growing number of peer-reviewed studies have confirmed his finding and identified some 20 substances as obesogens.
The role of these chemicals has been acknowledged by the presidential task force on childhood obesity, and the National Institutes of Health has become a major funder of research on links between endocrine disruptors and both obesity and diabetes.
Just this month, a new study in the journal Environmental Health Perspectives found that endocrine disruptors that are sometimes added to PVC plastic cause mice to grow obese and suffer liver problems — and the effect continues with descendants of those mice, generation after generation.
Another study found that women with a pesticide residue in their blood bore babies who were more likely to be overweight at the age of 14 months. That’s a common thread: The most important time for exposure appears to be in utero and in childhood so the greatest impact seems to be on fetuses and on children before puberty. However, limiting or eliminating exposure to these chemicals at any age seems the smart thing to do.
The magazine Scientific American recently asked whether doctors should do more to warn pregnant women about certain chemicals. It cited a survey indicating that only 19 percent of doctors cautioned pregnant women about pesticides, only 8 percent about BPA (an endocrine disruptor in some plastics and receipts), and only 5 percent about phthalates (endocrine disruptors found in cosmetics and shampoos). Dr. Blumberg, the pioneer of the field, says he strongly recommends that people — especially children and women who are pregnant or may become pregnant — try to eat organic foods to reduce exposure to endocrine disruptors, and try to avoid using plastics to store food or water. “My daughter uses a stainless steel water bottle, and so do I,” he said.
For all the uncertainty, these latest studies are one more reason to worry that endocrine disruptors may be the tobacco of our time. Science-based decisions to improve public health — like the removal of lead from gasoline — have been among our government’s most beneficial public policy moves. In this case, a starting point would be to boost research of endocrine disruptors and pass the Safe Chemicals Act. That measure, long stalled in Congress, would require more stringent safety testing of potentially toxic chemicals around us.
After all, which mouse would we rather look like?
