At least one man who ate several bags of butter-flavored microwave popcorn each day has developed a life-threatening lung disease possibly caused by an additive in the popcorn, his doctor says, and US regulators have launched an investigation.

The US Food and Drug Administration said it received a report from a Denver doctor saying the man has the lung disease similar to an illness affecting workers in plants where microwave popcorn is made, FDA spokesman Michael Herndon said in an e-mailed statement.

'We are currently evaluating the recent information on the association of inhalation of the food additive diacetyl with lung disease, and are carefully considering the safety and regulatory issues it raises,' Herndon said.

'This is the first time we're being made aware of a potential consumer case. We're taking (the doctor's) report very seriously,' said Bernadette Burden, a spokeswoman for the U.S. Centers for Disease Control and Prevention.

ConAgra Foods, maker of Orville Redenbacher and Act II microwave popcorn brands, said it will drop diacetyl from its butter-flavored microwave popcorn in the 'near future' to safeguard its employees.

The additive, which gives microwave popcorn a buttery taste, has long been linked with a rare lung disease, bronchiolitis obliterans, found in plant workers.

 In April, the CDC said workers at factories that make food flavorings as well as popcorn factories are at risk of contracting the hard-to-treat condition, which causes symptoms such as cough and shortness of breath, but steadily worsens.

ConAgra spokeswoman Stephanie Childs said that after months of deliberations, the company now expects to remove diacetyl 'within a year' to protect employees who are exposed to large amounts of the additive.

 'We made that decision in order to provide our employees with the safest work environment possible, but also to eliminate even the perception of concern for consumers,' Childs said.

Last month, Weaver Popcorn Co, maker of Pop Weaver microwave popcorn, said it had removed diacetyl from its microwave popcorn, in part to address consumers' concerns about the ingredient.

Dr Cecile Rose, of the National Jewish Medical and Research Center in Denver, has reported that a patient has contracted the disease from the daily consumption of several bags of butter-flavored microwave popcorn for several years.

Rose, in a July 18 letter to the FDA, described a patient who developed progressively worsening respiratory symptoms that resemble the ones described by workers affected by bronchiolitis obliterans, which has been linked to inhaling the food additive diacetyl.

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

No other details about the man were immediately available.

The Flavor and Extract Manufacturers Association of the US said it is concerned about the new development.

'This new information ... suggests a possible association between inhaling the fumes from the preparation of several bags of heavily butter-flavored microwave popcorn each day when the butter flavor contains the flavor ingredient diacetyl and the development of the patient's severe respiratory illness,' it said in a statement

'The information does not suggest a risk from eating the popcorn,' the group said.

Deirdre Flynn, executive director of Popcorn Institute, which represents US popcorn makers, could not say exactly where the flavor ingredient is used.

'To my knowledge it's used worldwide,' she said.

It could not be immediately determined how many bags of the popcorn are sold each year. Reuters