We're accustomed to hearing that too much couch time can make us fat. But it's not just sitting around that's making us fat, it may be the couch itself.
Researchers at the University of New Hampshire say that synthetic flame retardants used in couches and other furnishing and home electronics have been found to cause metabolic and liver problems that can lead to insulin resistance, which is a major cause of obesity.
"Being obese or overweight increases one's risk of many diseases including Type 2 diabetes, high blood pressure, coronary heart disease, stroke, gall bladder disease, osteoarthritis, sleep apnea and certain cancers," said Gale Carey, professor of nutrition and the lead researcher.
Carey and her team of researchers found that laboratory rats exposed to polybrominated diphenyl ethers, or PBDEs, experienced a disruption in their metabolism that resulted in the development of metabolic obesity and enlarged livers.
"Despite the plethora of resources devoted to understanding the roles of diet and exercise in the obesity epidemic, this epidemic continues to escalate, suggesting that other environmental factors may be involved. At the biochemical level there is a growing body of experimental evidence suggesting certain environmental chemicals, or 'obesogens', could disrupt the body's metabolism and contribute to the obesity epidemic," she said.
In Carey's research, fat cells isolated from rats dosed with high levels of flame retardants daily for one month developed a sensitivity to hormones that was similar to the sensitivity experienced by people who are overweight: the fat cells became more sensitive to epinephrine and less sensitive to insulin.
"One of the hallmarks of somebody who is becoming diabetic - and often this accompanies weight gain - is that their fat cells become sluggish in their response to insulin. With epinephrine, the fat cells more easily release the fatty acids into the blood stream and if those fatty acids are not used, they promote insulin resistance," Carey said.
"Those two features - insulin resistance and epinephrine sensitivity - are two features of fat cells from people who are above normal weight. And that's what we were seeing in our rats. Even though our rats had not gained weight, they were experiencing 'metabolic obesity'," she said.
The cause of the flame retardant-induced insulin resistance is unknown but one possibility is the suppression of a key metabolic enzyme in the liver. Carey and her students found that the activity of the enzyme, which is responsible for sugar and fat metabolism, dropped by nearly 50 percent in livers of rats exposed to flame retardants for just one month, compared to controls.
For more than 10 years, Carey and more than a dozen graduate and undergraduate students have collaborated with researchers from several universities and industries across the nation to examine the persistent organic environmental chemicals that could impact human health.
"The average person probably has about 300 chemicals in her body that are manmade," she said.
In a previous study, Carey and a graduate student examined the amount of flame retardant chemicals in breast milk. They found that the levels of these chemicals in breast milk are about two orders of magnitude greater than in European countries that do not allow the use of flame retardant chemicals.