NIEHS rodent study shows diacetyl is harmful to lungs

by Eric Schroeder
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WASHINGTON — New findings from researchers at the National Institute of Environmental Health Sciences (NIEHS) and Duke University show that exposure to diacetyl may be harmful to the nose and airways of mice. Diacetyl, which is naturally occurring in a variety of foods, including butter, milk, cheese, fruit, wine and beer, has been investigated as a possible cause of popcorn plant workers developing bronchiolitis obliterans (OB). Respiratory symptoms of the disease include cough and shortness of breath, according to the National Institute for Occupational Safety and Health.

According to the study’s findings, when laboratory mice inhaled diacetyl vapors for three months, they developed lymphocytic bronchiolitis — a potential precursor of OB. None of the mice were diagnosed with OB, though.

"This is one of the first studies to evaluate the respiratory toxicity of diacetyl at levels relevant to human health," said Daniel L. Morgan, Ph.D., head of the Respiratory Toxicology Group at the NIEHS and co-author on the paper that appeared on-line in the journal, Toxicological Sciences. "Mice were exposed to diacetyl at concentrations and durations comparable to what may be inhaled at some microwave popcorn packaging plants."

The authors concluded that workplace exposure to diacetyl contributes to the development of OB in humans, but cautioned that more research is needed.

The NIEHS said exposure of laboratory animals by inhalation closely duplicates the way humans are exposed to airborne toxicants, but some anatomical differences between mice and humans may account for why the nasal cavity of mice is more susceptible to reactive vapors than that of humans. Another reason may be that mice breathe exclusively through their noses, the NIEHS said.

The researchers also said the extensive reaction of diacetyl vapors in the nose and upper airways of mice may have prevented toxic concentrations from penetrating deeper in the lung to the bronchioles or tiny airways where obstruction occurs in humans.

The National Toxicology Program, headquartered at the NIEHS, said it plans to do a larger set of studies to provide inhalation toxicity data on artificial butter flavoring. The studies are expected to help pinpoint more definitively the toxic components of artificial butter flavoring and potentially help identify biomarkers for early detection. The data then will be shared with public health and regulatory agencies so they may establish safe exposure levels for the compounds and develop guidance to protect the health of workers in occupations where the chemicals are used.

Late last year, ConAgra Foods, Inc., Omaha, reformulated its Orville Redenbacher’s and ACT II microwave popcorn brands with a new butter flavoring that has no added diacetyl. In August, Weaver Popcorn Co., Inc. eliminated diacetyl from its products.

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