Users of smokeless tobacco products have higher nicotine and carcinogen levels than those who smoke cigarettes, according to a recent study.

Researchers found that U.S. adults who used only smokeless tobacco products had higher levels of biomarkers of exposure to nicotine and a cancer-causing toxicant -- the tobacco-specific nitrosamine NNK -- compared with those who used only cigarettes.

"Levels of biomarkers of exposure to nicotine and the cancer-causing tobacco constituent NNK were higher among exclusive smokeless tobacco users than exclusive cigarette smokers. This continues to put smokeless tobacco users at risk for adverse health effects, including cancer," Brian Rostron, an epidemiologist in the Center for Tobacco Products at the U.S. Food and Drug Administration (FDA), said in a statement.

: Even though smokeless tobacco is used less than cigarettes, it continues to be used among several population groups, particularly men and young people, which is a cause for concern because it has been found to have several adverse health effects and identified as a cause of cancer.

"Previous small studies have found high levels of toxic constituents including carcinogens [cancer-causing agents] in smokeless tobacco users, but analyses of nationally representative data have been generally lacking to date," Rostron said.

For the study, researchers collected and analyzed data from more than 23,600 adults who participated in the [National Health and Nutrition and Examination Survey] from 1999 to 2012. Participant-reported cigarette and smokeless tobacco use was used to categorize individuals into four groups. There were 16,313 nontobacco users, 488 exclusive smokeless tobacco users, 6,791 exclusive cigarette smokers, and 92 dual cigarette and smokeless tobacco users.

The geometric mean serum level of cotinine, the biomarker of nicotine exposure, was higher in exclusive smokeless tobacco users compared with exclusive cigarette smokers: 178.9 nanograms per milliliter (ng/ml) versus 130.6 ng/ml. The geometric mean urine level of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), the biomarker of NNK exposure, was also higher in exclusive smokeless tobacco users compared with exclusive cigarette smokers: 583.0 picograms per milligram (pg/mg) of creatinine versus 217.6 pg/mg of creatinine.

"Our findings demonstrate the need for continuing study of the toxic constituents of smokeless tobacco as well as their health effects on the individuals who use them," Rostron said." This is why the FDA and CDC [Centers for Disease Control and Prevention] are continuing to analyze and monitor biomarker levels among tobacco users and why the FDA and NIH [National Institutes of Health] are collaborating on the Population Assessment of Tobacco and Health (PATH) Study, a large longitudinal study in which biospecimens such as blood and urine have been collected."

The findings are detailed in the journal Cancer Epidemiology, Biomarkers & Prevention.