Smokeless tobacco is used far less than cigarettes, primarily among men and young people, but it has become a cause for concern due to links with adverse health effects and identification as a cause of cancer.

Survey results and biomarkers published in Cancer Epidemiology, Biomarkers&Prevention, a journal of the American Association for Cancer Research, find 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 only used cigarettes.

 Brian Rostron, PhD, an epidemiologist in the Center for Tobacco Products at the U.S. Food and Drug Administration (FDA)
, and colleagues analyzed data on biomarkers of exposure to seven tobacco constituents, including nicotine and tobacco-specific nitrosamine, available from 23,684 adults who participated in NHANES [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 non-tobacco 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.

"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," said Rostron. "Our analysis of data from NHANES, a large, nationally representative study of U.S. health behaviors and outcomes, generated results consistent with those from previous smaller studies. 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.

However, the nature of the data collected in NHANES is a limitation to the study. For example, because NHANES is a general health survey, there is no detailed information on the type of smokeless tobacco product used; there is no information on the quantity of the smokeless tobacco product used; and there is no information on duration or former use of smokeless tobacco products.