Occupational risk: Popcorn is at the centre of a new occupational lung disease, according to findings presented at the European Respiratory Conference, in Glasgow.
Dr Kathleen Kreiss, of the Centre for Disease Control (CDC) in Atlanta, said medical research discovered that a substance called diacetyl - a ketone that gives popcorn a buttery flavour - caused one in three workers at a popcorn factory in Kansas to develop a rare lung disease.
Bronciolitis obliterans is a rare inflammatory condition of the small airways in the lung. It causes a fixed airways obstruction, leading to symptoms such as shortness of breath and cough.
In the most severe cases, sufferers may require lung transplants.
In 2000, an occupational physician informed the Missouri health authorities of eight suspected cases of airways obstruction in young people working in a popcorn factory in Kansas.
Following a lengthy investigation, the workers in the "mixing" section of the factory - who mix the flavouring with the soya oil used in popcorn manufacture - were found to have the highest frequency of the condition, as well as the highest direct exposure to diacetyl.
The second most exposed category was the "packagers", whose job was to put the maize grains in microwaveable bags with the oil and the flavouring mixture. It emerged that the original eight workers were only the tip of the iceberg.
Dr Kreiss told the conference the factory's 122 workers had two-and-a-half times more respiratory problems than the general population with much reduced lung function.
"All workers in popcorn factories should use respirators supplied with purified air," she said. "The internal organisation of the plants must be reviewed to provide better ventilation and double doors separating the mixing area from the rest."
Pointing out that only 15 per cent of smokers develop obstructive lung disease and 20 per cent of patients with chronic bronchitis have never smoked, she said doctors must be vigilant for work-related causes of lung disease. "I suspect other cases will be found in the food industry, especially where flavourings are subjected to heat," Dr Kreiss said. "There can be little doubt that there are many more 'popcorn cases' waiting to be discovered in a wide range of industries where too little attention has been paid to the harmful effects of reactive, volatile substances," she concluded.