Consumers, not just factory workers, may be in danger from fumes from the buttery flavouring in microwave popcorn, according to a warning letter to U.S. federal regulators from a doctor at a leading lung research hospital.

'We cannot be sure that this patient's exposure to butter-flavoured microwave popcorn from daily heavy preparation has caused his lung disease ... however, we have no other plausible explanation.'—Dr. Cecile Rose

A pulmonary specialist at Denver's National Jewish Medical and Research Center has written to federal agencies to say doctors there believe they have the first case of a consumer who developed lung disease from the fumes of microwaving popcorn several times a day for years.

"We cannot be sure that this patient's exposure to butter-flavoured microwave popcorn from daily heavy preparation has caused his lung disease," Dr. Cecile Rose cautioned in the letter. "However, we have no other plausible explanation."

The July letter, made public Tuesday by a public health policy blog, refers to a potentially fatal disease commonly called popcorn lung that has been the subject of lawsuits by hundreds of workers at food factories exposed to chemicals used for flavouring.

In response to Rose's finding, the Flavour and Extract Manufacturers Association issued a statement Tuesday recommending that its members reduce "to the extent possible" the amount of diacetyl in butter flavourings they make. It noted that diacetyl is approved for use in flavours by the U.S. Food and Drug Administration.

Weaver Popcorn Co. replacing butter flavouring

One national popcorn manufacturer, Weaver Popcorn Co. of Indianapolis, said last week it would replace the butter flavouring ingredient because of consumer concern. Congress has also been debating new safety measures for workers exposed to diacetyl in food-processing plants.

On Wednesday, ConAgra Foods Inc. said it will stop using diacetyl in its Orville Redenbacher and Act II microwave popcorns out of concern for its workers' health.

The FDA said in an e-mail it is evaluating Rose's letter and "carefully considering the safety and regulatory issues it raises."

Fred Blosser, a spokesman for the National Institute for Occupational Safety and Health, said it is the first case the U.S. institute has seen of lung disease apparently linked to popcorn fumes outside the workplace. The institute, which is the occupational safety arm of the Centers for Disease Control and Prevention, said it is working on a response to the letter.

William Allstetter, a spokesman for National Jewish Medical, confirmed the letter was sent by Rose, a specialist in occupational and environmental lung diseases and director of the hospital's Occupational and Environmental Medicine Clinic.

"There have been no other cases that we know of other than the industrial occupational ones," Allstetter said.

Patient suffered coughing, shortness of breath

Rose acknowledged in the letter that it is difficult to confirm through one case that popping buttered microwave popcorn at home can cause lung disease. However, she said she wanted to alert regulators of the potential public health implications.

Rose said the ailing patient, a man whom she wouldn't identify, consumed "several bags of extra butter-flavoured microwave popcorn" every day for several years.

He described progressively worsening respiratory symptoms of coughing and shortness of breath. Tests found his ability to exhale was deteriorating, Rose said, although his condition seemed to stabilize after he quit using microwave popcorn.

She said her staff measured airborne levels of diacetyl in the patient's home when he cooked the popcorn. The levels were "similar to those reported in the microwave oven exhaust area" at the quality assurance unit of the popcorn plant where the affected employees worked, she said.