Carcinogens from smoking and smokeless tobacco use (1)
The authors are correct in this conclusion, as some forms of smokeless tobacco have been shown to be associated with oral cancer, other oral lesions, and may also increase some cardiovascular risks. The idea that smokeless tobacco is not safe is unlikely to be surprising to many people. But given that many of the major cigarette manufacturers are currently test-marketing smokeless tobacco products it may be worth examining the types and risks from smokeless tobacco in more detail, and also looking at how the epidemiological data relates to the recent findings from Hecht and colleagues.
The first thing that needs to be said about smokeless tobacco is that it is not just one thing. The extremely wide variety of different types of smokeless tobacco can be viewed on an excellent website produced by the U.S. National Cancer Institute and Centers for Disease Control, online at: www.cancercontrol.cancer.gov/tcrb/stfact_sheet_combined10-23-02.pdf.
Secondly, smokeless tobaccos vary enormously in the amount of toxins (including carcinogens) they deliver, and (not surprisingly) the ones containing higher concentrations of toxins (like carcinogenic tobacco-specific nitrosamines, or benzo(a)pyrene), appear to be more likely to have adverse health effects. To give an idea of the range of concentrations of toxins, Professor Brad Rodu at University of Louisville published data on the concentration of carcinogenic Tobacco-Specific Nitrosamines (TSNAs) in various smokeless tobacco products. Some examples are as follows (the units of measurement are parts per million based on dry weight):
Ariva (new powdered tobacco lozenge): <0.1 ppms
Ettan (Swedish snus): 2.0 ppms
Red Man (US chewing tobacco): 1.8 ppms
Copenhagen (leading US moist snuff): 12.1 ppms
Red Seal (US dry snuff): 1096 ppms
So we have here over a thousand-fold difference in the concentration of certain toxins in different types of smokeless tobacco! There are a few additional problems. Most of the smokeless tobacco products sold in the United States use fermentation in their production. This facilitates the development of carcinogenic compounds in the tobacco. In fact there is evidence to show that in these fermented products, they continue to ferment in the can, such that the concentration of carcinogens may increase in the can as it sits on the shelf. The method of production used for Swedish snus does not include fermentation, but rather uses a pasteurization-like process that treats the product with steam and appears to kill the microbes required for fermentation. This is thought to be the reason why Swedish snus has lower levels of carcinogens than US Smokeless tobacco. It may also be the reason that Swedish snus does not appear to cause oral cancer. However, the problem remains in the United States that the tobacco manufacturers can adjust the way they produce their products and the ingredients included in them without telling anyone. That is part of the reason why many experts support the pending legislation that would give the FDA the power to regulate tobacco products. This legislation appears to enable the FDA to require maximum permissible levels of harmful toxins in both smoked and smokeless tobacco products. With cigarettes the problem of what happens when you burn the product and inhale the smoke remains, but for smokeless there is a real prospect of offering a product that contains and delivers a known maximum level of toxins – and potentially a level that would be extremely unlikely to cause cancer. But for now, as demonstrated in Hecht and colleagues study, US smokeless tobacco delivers more toxins than necessary and there is little we can do about it.
In my next post I’ll discuss the relationship between the concentration of toxins in smokeless tobacco products and their harmfulness to health.
If you are interested in the views of tobacco and cancer experts on this topic you can learn more by reading the article linked below: