The investigators pointed out that previous studies have already linked diacetyl to respiratory and other health problems among workers at microwave popcorn and food-flavoring plants.

Although diacetyl forms naturally in fermented beverages, such as beer and wine, its chemical structure is similar to a substance that makes beta-amyloid proteins clump together in the brain. This clumping, the study authors noted, is a hallmark of Alzheimer's disease.

In their study, the researchers found that diacetyl also increases the amount of beta-amyloid clumping in the brain. And it worsened the beta-amyloid protein's harmful effects on nerve cells grown in a lab when the cells were exposed to the same levels of diacetyl that factory workers might be exposed to in their jobs.

The study authors pointed out that other experiments revealed that diacetyl also crosses the "blood-brain barrier," which helps protect the brain from dangerous substances. Diacetyl also prevented a beneficial protein from protecting nerve cells.

"In light of the chronic exposure of industry workers to diacetyl, this study raises the troubling possibility of long-term neurological toxicity mediated by diacetyl," Robert Vince and colleagues concluded in a news release from the American Chemical Society.

The study was funded by the Center for Drug Design research endowment funds at the University of Minnesota.

While the study found an association between chronic diacetyl exposure and certain brain protein processes, it did not prove a cause-and-effect relationship.