An Informative Study on Tobacco-Specific Nitrosamines

Last week, I noted that University of Minnesota researchers, arguing for additional reductions of tobacco-specific nitrosamines (TSNAs) in moist snuff products (here), complained that “No evidence has been found that Conwood [a Reynolds company] and USST [United States Smokeless Tobacco, an Altria company] took any meaningful steps to reduce the relatively high levels of NNN and NNK in their products.” (The lead author was Stephen Hecht.)

The Hecht allegations are another false alarm, as a new study in Food and Chemical Toxicology (abstract here) provides evidence that, “…since 1997, average TSNA levels have declined by approximately half in USST moist smokeless tobacco products.” The authors, including lead author Michael Fisher, are from Altria.

Fisher et al. provide valuable information about how agricultural and production practices influence TSNA development. They collected samples from thousands of bales of tobacco over the past 15 years, and discovered that “…there is a general relationship between average rainfall during the tobacco curing season and TSNA in cured tobacco.”

Moist snuff is primarily made from dark-leaf tobacco, grown in western Tennessee and western Kentucky, and barn-cured in late-summer and autumn with smoke from hardwood fires. Fisher et al. show that the most important factors in TSNA formation are humid and/or moist curing conditions. Excess nitrogen fertilizer is also a factor, although tobacco needs high concentrations of nitrogen in order to thrive. As Hecht et al. pointed out in their article, American moist snuff has marginally higher TSNA levels than Swedish snus, which is also made with dark-leaf tobacco that is air cured. This suggests that fire curing may also play a minor role in TSNA formation.

In the past manufacturing may have also played a small role in TSNA formation, when particular bacterial strains used some of the nitrogen (in the form of nitrate) to form nitrite. The nitrate-reducing bacteria may be present in harvested tobacco, and in fermentation facilities, but in 2005 USST initiated strict sanitation practices and other programs to inhibit these bacteria. This resulted in TSNA levels in finished products that were consistent with the levels found in the incoming leaf.

As I have noted previously, TSNA levels in moist snuff products from Altria and Reynolds are at historically low levels. This study documents that TSNA levels are mainly influenced by weather conditions during the curing process. Furthermore, it is important to emphasize that there is no evidence that current TSNA levels are associated with ANY significant cancer risks.