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

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 flavored microwave popcorn from daily heavy preparation has caused his lung disease," cautioned Dr. Cecile Rose. "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 flavoring.

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

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

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, spokesman for the National Institute for Occupational Safety and Health, said it is the first case the institute has seen of lung disease apparently linked to popcorn fumes outside the workplace.

The occupational safety arm of the Centers for Disease Control and Prevention said it is working on a response to the letter.

William Allstetter, 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.

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 flavored 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.

David Michaels, of the George Washington University School of Public Health, who first published Rose's letter on his blog, The Pump Handle, said the finding is another reason for federal regulators to crack down on diacetyl exposure by workers and consumers.

"This letter is a red flag, suggesting that exposure to food flavor chemicals is not just killing workers, but may also be causing disease in people exposed to food flavor chemicals in their kitchens," Michaels wrote on his public health policy blog

If you can't eat popcorn, what the hell can you do?