Animal study links flame retardant to obesity

Mice fed high-fat diets gained about 30 percent more weight than other mice eating the same foods when they also ingested high doses of a flame retardant, according to a new study out of Japan.

It’s the first study to show that a brominated flame retardant may accelerate weight gain, raise blood sugar, and contribute to metabolic disorders such as diabetes.

The flame retardant, hexabromocyclodecane (HBCD), is used in building materials and insulation. It accumulates in the tissues of animals and humans, and previous animal studies have shown that it may disrupt hormones, metabolism, and immune systems.

Too many calories plus not enough exercise are major obesity drivers, but emerging evidence suggests that exposure to some hormone-disrupting chemicals, particularly in early development, may also play a role.

Some evidence, mostly with lab animals, suggests that prenatal exposure to these “obesogens” can reprogram metabolism, leading to more fat cells and raising the risk of obesity later in life, particularly in those eating high-calorie or high-fat diets.

The findings suggest that HBCD “may contribute to enhancement of diet-induced body weight gain and metabolic dysfunction”, the authors wrote in the study published online last week in the journal Environmental Health Perspectives.

In the study, researchers split 46 adult male mice into groups receiving either a high-fat or normal diet with or without a flame retardant over a 15-week period.

The mice fed a high-fat diet with a high dose of the flame retardant gained an average of 21 grams while mice fed the same diet without the chemical gained about 16 grams. While five grams doesn’t seem like much, to a mouse, the difference is substantial. At the onset, the mice weighed, on average, 21 grams. That means mice fed the high-fat diet plus high levels of flame retardant doubled their weight.

No link to obesity, however, was found in the mice that ate a normal diet, even if they were dosed with the flame retardant. “In contrast, no alterations in body and liver weight were observed in normal-diet–fed mice with or without HBCD,” the authors wrote.

The daily doses of HBCD associated with the increased weight gain were substantially higher than the average estimated dietary intake of people. Diet is considered the most important route of exposure for people, although they also are exposed through indoor dust and air, the study authors wrote.

The mice fed the flame retardant also had higher blood sugar and higher insulin levels than the unexposed mice. Their livers also weighed more and their adipose tissues were inflamed. Changes also were noted in the gene expression of their glucose transporters.

The authors said this metabolic dysfunction can accelerate obesity. “These results suggest that HBCD may contribute to metabolic dysfunction via an interaction with diet, i.e., HBCD may be an ‘enhancer obesogen’,” they wrote.

The mice on the high-fat diet got more than 60 percent of their daily calories from fat. For people, it’s recommended that 20 percent to 35 percent of daily calories come from fat. The high-fat diet was also higher in calories than the normal diet.

The U.S. is investigating alternatives to HBCD, and the United Nations has recommended that it be phased out. However, it is still used in large volumes. The U.S. Environmental Protection Agency estimates that 10 to 50 million pounds were manufactured or imported in the U.S. in 2005.

[A November 2011 Environment Canada screening-asssessment report said: “It is concluded that HBCD is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.” In May 2013, the Stockholm Convention on Persistent Organic Pollutants voted for a global ban of the flame retardant, aiming for its elimination by treaty members by 2019.—GS]

Other chemicals linked to obesity or diabetes in animal or human studies include phthalates, perfluorinated chemicals, bisphenol A, arsenic, tributyltin and chlorinated compounds such as dioxins, PCBs, and DDT.