It had been suggested that diacetyl, one of the compounds that gives butter its distinctive yummy flavor (and a key ingredient in margarines and oils), could pose severe health risks when heated and inhaled for long periods of time.
In fact, workers in several factories churning out artificial butter flavoring have come down with a rare and dire disease of the lungs called bronchiolitis obliterans. Most of the cases have been found in young, healthy, non-smoking men, and there are no known cures for the disease except a lung transplant.
Now a new study confirms that prolonged exposure to diacetyl can be harmful to the nose and airways of mice. When laboratory mice inhaled diacetyl vapors for three months, they developed lymphocytic bronchiolitis -- a potential precursor of obliterative bronchiolitis.
"Mice were exposed to diacetyl at concentrations and durations comparable to what may be inhaled at some microwave popcorn packaging plants," said Daniel L. Morgan, Ph.D., head of the Respiratory Toxicology Group at the National Institute of Environmental Health Sciences (NIEHS) and co-author of the paper that appears online in the journal Toxicological Sciences.
Anatomical differences between mice and people - for instance, mice breathe only through their noses -- might explain why the rodents' nasal cavity was so susceptible to the vapors, preventing toxic amounts from penetrating deeper in the lungs, where the small airways of humans are obstructed.
This study, however, is only the beginning. The National Toxicology Program at the NIEHS plans to do a larger set of studies to gather and compare data on another compound in artificial butter flavoring called acetoin. The studies will help identify with more certainty the toxic components of artificial butter flavoring, and the data will be shared with public health and regulatory agencies to develop guidelines for safe exposure levels.
Still, several watchdog groups have already called for stronger measures to regulate diacetyl. There is one known case of a consumer diagnosed with the same disease afflicting the factory workers, but he ate at least two bags of buttery microwave popcorn every day for a decade, effectively reproducing factory conditions in his kitchen. At the very least, you might want to check the packaging next time you're in the grocery aisle ...