Lab tests performed in Minnesota on illicit THC vaping products have solidified the role of vitamin E acetate in an outbreak of severe lung injuries among e-cigarette users across the nation this year.

The tests found vitamin E in illicit vaping products that were seized by Minnesota law enforcement agencies in 2019, at the height of the outbreak, but not in products seized in 2018, before the outbreak, the Minnesota Department of Health reported on Tuesday.

The state’s findings were circulated nationally on Tuesday by the U.S. Centers for Disease Control and Prevention, which has monitored the outbreak nationally and has reported 2,290 cases of vaping-associated lung injuries this year and 47 related deaths.

“We now have evidence of vitamin E acetate in the lungs of Minnesotans and in illicit THC products from Minnesota during the outbreak,” said Jan Malcolm, state health commissioner. “We have more work ahead, but every bit of evidence gets us closer to a resolution.”

Minnesota has reported 125 confirmed or probable cases of the lung illness, including three deaths and multiple cases in which otherwise young, healthy people required intensive care and mechanical breathing assistance for treatment.

Vitamin E acetate came under suspicion after it was discovered in fluid samples from the lungs of injured patients. Health officials have speculated that vitamin E was added to illicit vaping products this year as a thickener or to dilute the concentration of THC, the psychoactive component of marijuana.

“It is something that one can put the THC into, and because it’s thick, it still gives the appearance that you’re getting a good product,” said Dr. Ruth Lynfield, state epidemiologist and co-author of the CDC report.

The acetate was found in all 20 THC products seized by law enforcement agencies in Minnesota in 2019, but in none of the 10 products seized in 2018.

It also was found in samples of illicit THC vaping products provided to state health authorities by 11 of 12 lung-injured patients.

Lynfield said the finding is preliminary and based on a small number of product samples, and she said other compounds could be playing a role. Research now needs to move beyond the association between vitamin E and vaping injuries to prove how exposure to one causes the other, she said.

The discovery in some ways conflicts with findings by Mayo Clinic doctors in Arizona, who used imaging scans to conclude that vaping lung injuries were caused by inhalation of toxic chemicals.

Lynfield said it’s possible that vitamin E is interacting with inhaled chemicals or other substances in a way that causes the injuries. CDC studies of biopsies from lung-injured patients, including patients who died, should help reconcile differences in the research findings, she said.

“It will be very important to understand how their results and their findings compare with the results from Mayo,” she said.

Lynfield said it will also be important for researchers to determine if there is a dose level of vitamin E that leads to injury.

While research continues to identify illicit THC and vitamin E acetate as culprits in the outbreak, health officials still discourage broader forms of e-cigarette usage.

Children, young adults and pregnant women are discouraged from vaping any products, including legal nicotine forms. All people are discouraged from vaping illicit THC.