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March 13, 2008 -- A new study shows signs of lung damage in mice exposed to diacetyl, a chemical used in artificial butter flavoring.
Leading popcorn makers say they no longer use diacetyl in their products. But diacetyl is still used in other processed foods.
In the new study, mice developed lung damage when exposed to levels of diacetyl fumes found in flavoring factories.
Previous research has linked diacetyl fumes to a rare, life-threatening lung disease called bronchiolitis obliterans in workers in the flavor industry.
Bronchiolitis obliterans makes it difficult for air to flow out of the lungs. Excessive exposure to diacetyl in flavor factories could raise the risk of developing bronchiolitis obliterans.
Last September, one case of bronchiolitis obliterans was reported in a man who ate two or more bags of microwave popcorn daily.
The FDA?classifies diacetyl as being "generally recognized as safe."?Last September, the FDA?received a citizens' petition to revisit diacetyl's safety status. An FDA?spokesperson says the FDA isn't aware of any evidence that consuming diacetyl is unsafe.
Researcher Daniel Morgan, PhD, of the National Institute of Environmental Health Sciences, spoke with WebMD about the new study.
"The consumer would not be exposed to these concentrations," Morgan tells WebMD. "The amounts in these factories are much higher. They're using the concentrated butter flavoring, and they're heating it, and they're getting the concentrated vapors.
"There's a lot of concern about whether it's safe to eat microwave popcorn at home. I think we have to understand that the amounts of diacetyl present in foods and in the microwave popcorn is very low. And to my knowledge, there are no data showing it's unsafe to consume food containing diacetyl. This is primarily an occupational-type hazard," says Morgan.
Morgan notes that rodents, unlike people, only breathe through their noses, which may have affected the study's results.
"The nose cleans and humidifies air we inhale before it gets to the lungs. probably do a much better job than humans do of taking out the diacetyl before it gets to the small airways," Morgan says.
The mice in Morgan's study didn't develop bronchiolitis obliterans. More research is needed to see if longer exposure to diacetyl fumes causes bronchiolitis obliterans.
"What we're seeing in our study that we published was perhaps just early stages," says Morgan. "We don't know for sure."
Morgan notes that diacetyl is "used in a number of snack foods -- chips and things like that. And I think there's probably a problem there also with worker exposure. That hasn't been investigated to any great extent."
Morgan's study recently appeared in the advance online edition of Toxicology Sciences.
ConAgra Foods, General Mills, American Pop Corn Co., and Weaver Popcorn Co. say they no longer add diacetyl to their microwave popcorn products, which include Orville Redenbacher, Act II, Pop Secret, Jolly Time, and Pop Weaver.
Last September, the U.S. House of Representatives passed a bill calling for stricter standards to protect workers exposed to diacetyl in popcorn plants. The Senate hasn't yet voted on that bill.