Daily exposure to the fumes from buttery flavoring in microwave popcorn may lead to lung cancer for consumers, according to a warning letter to federal regulators from a doctor at a leading lung research hospital. 

 Dr. Cecile Rose, a pulmonary specialist at Denver's National Jewish Medical and Research Center, has written to federal agencies to say he and colleagues 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."

Written in July, the letter 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.