Denver ? 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.