CENTENNIAL, Colo. — Wayne Watson loved microwave popcorn so much he would eat at least two bags each night, breathing in the steam from the just-opened package, until doctors told him it may have made him sick.

Watson, whose case of "popcorn lung" is the sole reported case of the disease in a non-factory worker, said he is convinced his heavy consumption of popcorn caused his health problems.

In an interview with The Associated Press on Wednesday, the 53-year-old furniture salesman had a message to convey: "America: Read the labels, and just be careful about what we put into our bodies and always practice moderation," Watson said. "Don't go crazy."

Popcorn flavouring contains the chemical diacetyl, which has been linked to lung damage in factory workers testing hundreds of bags of microwave popcorn per day and inhaling its fumes. The chemical is a naturally occurring compound that gives butter its flavour and is also found in cheese and even wine, according to the National Institute of Occupational Safety and Health.

It's been approved by the Food and Drug Administration as a flavour ingredient, but hundreds of workers have sued flavouring makers in recent years for lung damage.

There are no warnings from federal regulators, nor is there medical advice on how consumers should treat news of the rare, life-threatening disease, bronchiolitis obliterans, also known as popcorn lung.

Dr. Cecile Rose, a lung specialist at the National Jewish Medical and Research Center in Denver who diagnosed Watson's case in February, told the AP that no definite link has been established between Watson's heavy popcorn consumption and his lung disease, but that "the possibility raises public health concerns."

Doctors tested Watson's home for levels of diacetyl fumes and found that while popcorn was microwaved in the kitchen, peak levels of the fumes were similar to those measured in factories, Rose said.

While she still lets her kids microwave popcorn at home, Rose said she is concerned that the high levels of fumes measured at Watson's home could be present anytime consumers microwave popcorn, and that these high levels -- and not just the cumulative effect of exposures in the factory -- could be a factor in causing the disease.

"We don't know yet. We think it's a possibility," said Rose, who recommended the popcorn bags be tested further.

On Wednesday, the nation's largest microwave popcorn maker, ConAgra, said it would stop using diacetyl within a year out of concern for its workers -- not because of risks to consumers. ConAgra makes Act II and Orville Redenbacher brands.

The Flavor and Extract Manufacturers Association said that Rose's finding does not suggest a risk from eating microwave popcorn.

Watson said he still craves popcorn but has taken his doctors' advice and snacks now on fruits and vegetables. He said his breathing has improved and he's lost 35 pounds. He no longer uses an inhaler or takes steroids.