The presence of highly carcinogenic tobacco-specific nitrosamines (TSNA) in snuff has been a matter of serious concern. However, the levels of TSNA in such products may differ by orders of magnitude depending on origin and manner of processing, and the mere presence of such agents at low levels does hardly constitute a meaningful prerequisite for classifying all types of snuff as human carcinogens. Reviewing available epidemiological evidence, a wide discrepancy is found for estimated cancer risk associated with snuff dipping derived from on one hand previous investigations conducted in the United States and on the other from recent extensive Swedish epidemiological studies. In spite of the fact that approximately 20% of all grown-up Swedish males use moist snuff, it has not been possible to detect any significant increase in the incidence of cancer of the oral cavity or pharynx-the prevalence of which by international standards remains low in this country. Further, there is insufficient evidence for a causal link between the use of Swedish snuff and increased risk for cardiovascular disease. Dissimilarities in the content of TSNA in oral snuff products may represent one important reason for the different outcomes of the epidemiological surveys conducted in the United States and Sweden. Bioassays using pure TSNA in rodents appear to give exaggerated risk estimates for humans, a discrepancy that could be ascribed to species-related differences in the relation between exposure and DNA target dose and/or adduct repair rates, as well as to the presence of anticarcinogens in snuff. Although a small risk cannot be excluded, the use of smokeless tobacco products low in TSNA which now are available on the market entails a risk that at any rate is more than 10 times lower than that associated with active smoking. Nevertheless, due to the decisive role of potent TSNA in determining possible cancer risks in users of smokeless tobacco, and due to the fact that large variations in the concentrations may occur, adequate control measures should be taken to keep the levels of these nitrosamines in smokeless tobacco products as low as is technically feasible.
Copyright 1998 Academic Press.