The findings were presented at the American Chemical Society's annual meeting in Philadelphia.
The newly identified cancer-causing culprit in these products is (S)-NNN. It is part of a larger family of chemicals called nitrosamines. Nitrosamines are also found in such foods as beer and bacon. They form naturally in the stomach when people eat foods containing high levels of nitrite. Nitrosamine levels in smokeless tobacco are far higher than in food, according to a prepared statement.
Researchers fed rats a low dose of two forms of chemicals found in smokeless tobacco for 17 months. The doses were about equivalent to a person who used half a tin of smokeless tobacco every day for 30 years. (S)-NNN seemed to cause large numbers of oral and esophageal tumors in the rats, the study shows.
"There is a very specific oral carcinogen in smokeless tobacco and it is potent," says researcher Silvia Balbo, PhD. She is a cancer researcher at the Masonic Cancer Center of the University of Minnesota in Minneapolis.
This compound is found in all smokeless tobacco products, including those that look like breath mints, strips, or candy, and “snus,” which are pouches filled with tobacco that are placed between the upper lip and gum. E-cigarettes or vapors do not contain tobacco and do not fall into this category.
Is Smokeless Tobacco the Lesser of Two Evils?
Traditional cigarettes also have this cancer-causing chemical, but the risk for oral cancer may be related to what smokeless tobacco products do when they sit in the mouth versus when they are burnt and inhaled.
Balbo says the next step is to understand how, or if, the study findings apply to humans.
Many people may view smokeless tobacco products as safe as or safer than cigarettes. "We see more and more advertising for these products and they are not as badly viewed as smoking, but they are not harmless,” she says.
"Is jay walking safer than jay walking blindfolded?" asks Nathan Cobb, MD. He is a research investigator at the Schroeder Institute for Tobacco Research and Policy Studies at the American Legacy Foundation and a pulmonologist at Georgetown University, both in Washington D.C.
"You are not going to get lung cancer from them, but you will be at higher risk for other types of cancer,” he says.
We knew it was harmful, but we didn't know exactly how until now, says Richard B. Hayes, PhD. He leads the division of epidemiology at New York University Langone Medical Center in New York City.
"This study identifies an agent in smokelesss tobacco that causes cancer in animal models,” he says. But this is not to say that it's the only one. Hayes likens this to earlier hopes that adding filters to cigarette tips would lower smoking risks. Unfortunately, that didn't quite pan out.
"I would be concerned that people will think that taking this ingredient away would eliminate all risks and we do not know if that is true.”
Gilbert Ross, MD, medical director of the American Council on Science and Health in New York City, is an advocate of harm reduction and can see a use for smokeless tobacco, though. "Allowing smokers to get help in quitting their lethal addiction via safer nicotine delivery systems such as snus or e-cigarettes will reduce the huge toll of smoking,” he says.
Ninety-eight percent of tobacco-related disease is caused by smoking cigarettes, Ross says via email.
These findings were presented at a medical conference. They should be considered preliminary, as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.