New research indicates exposure to low levels of a flavoring chemical called diacetyl in combination with a mild case of influenza can cause serious lung damage. The findings, in mice, suggest those with occupational exposure to the chemical should be cautious of working while sick with respiratory infections.
Diacetyl is a naturally occurring chemical often found in cultured dairy products. Contributing to that characteristic “buttery” aroma and flavor, food manufacturers have long used the chemical as a flavoring in products such as microwave popcorn.
In the early 2000s it was discovered chronic exposure to high levels of diacetyl fumes can lead to a serious lung disease known as bronchiolitis obliterans. A number of high-profile lawsuits from factory workers suffering lung damage led to increased protections surrounding use of the chemical in industrial contexts.
More recently, researchers have started investigating the effects of lower-levels of exposure to diacetyl. Of particular interest have been contexts such as coffee manufacturing, where diacetyl fumes are generated as a natural byproduct of the bean roasting process.
In a new study, researchers from the University of Rochester Medical Center modeled in mice the kind of diacetyl exposure someone working in coffee roasting factories could face. The mice were exposed to diacetyl fumes for just one hour a day for five days.
No significant lung damage was detected in the mice following this kind of mild diacetyl exposure, but the results were completely different when the mice were given the same exposure while experiencing a mild influenza infection.
Within days of the “double hit,” the mice displayed significant lung impairments. Two weeks after exposure, around half of the influenza/diacetyl animals had died, whereas all animals in the control groups exposed to just diacetyl or influenza survived.
“We found that a single exposure to diacetyl for short periods of time did not result in much lung damage,” explained Matthew McGraw, lead author on the study. “But when mice are exposed to another common environmental exposure, like flu, the double hit can cause airway disease similar to what we see with high-dose, long-term exposures to diacetyl.”
It’s important to note these findings are only reported in animal studies at this stage. The researchers are planning to investigate lung disease in humans exposed to these lower levels of diacetyl, starting with those working in coffee roasting factories.
McGraw said one of the important takeaways from these findings is the concept of double-hit exposure. These are environmental exposures to chemicals that have been shown to be safe in low levels but when combined with other factors can cause long-term health problems.
"Our study shows that common environmental exposures that seem harmless on their own can have very serious impacts on lung function and long-term respiratory health when combined," said McGraw.
The study was published in the American Journal of Physiology – Lung Cellular and Molecular Physiology.
