RE: "CHRONIC DISEASE MORTALITY IN A COHORT OF SMOKELESS TOBACCO USERS"

Jon O. Ebbert1, Ping Yang1 and Scott L. Tomar2

1 Mayo Clinic Cancer Center, Mayo Clinic, Rochester, MN 55905
2 Division of Public Health Services and Research, University of Florida College of Dentistry, Gainesville, FL 32610-0405

We read with great interest a recently published article (1) and have several concerns about the design and conclusions of this study.

First, the hazard ratios for causes of death for exclusive smokeless tobacco users were calculated relative to "non-tobacco users." This category included pipe and cigar smokers, the number of which was not reported. National data suggest that 24 percent of US men were cigar or pipe smokers in 1970, approximately the time the First National Health and Nutrition Examination Survey was conducted (2). Data from the American Cancer Society’s Cancer Prevention Study II cohort and other studies suggest that, among men, cigar smoking increases the risk of death from cancer of the oral cavity and pharynx (rate ratio (RR) = 4.0, 95 percent confidence interval (CI): 1.5, 10.3), larynx (RR = 10.3, 95 percent CI: 2.6, 41.0), and lung (RR = 5.1, 95 percent CI: 4.0, 6.6) compared with never smokers (3). Prospective study data have suggested that pipe smoking among men is associated with increased mortality rate ratios for cancer of the oral cavity (range = 2.0–3.5), esophagus (range = 2.0–3.5), and lung (range = 2.1–3.0) (4). If pipe and cigar smoking increased the risk of death in this cohort, one may see no increased risk of death from smokeless tobacco when compared with "non-tobacco users" confounded by the inclusion of pipe and cigar smokers. Indeed, this is what the authors observed. The null effect of smokeless tobacco was more obvious in men than women, which would be expected because more men than women smoke pipes and cigars (2). Further, this study is underpowered for this type of analysis, considering that only two cancer deaths were observed among smokeless tobacco users.

Second, smokeless tobacco use among men in the early 1970s was far more likely to be in the form of chewing tobacco rather than snuff (2). Chewing tobacco appears to have substantially lower levels of tobacco-specific N-nitrosamines than snuff (5) and probably carries lower carcinogenic potential. Female smokeless tobacco users in the early 1970s were more likely to use snuff than chewing tobacco (2). This may explain why the observed hazard ratio point estimate for cancer mortality was greater for women than for men. The contemporary applicability of the study conclusions may be questionable if analysis of the 2000 National Health Interview Survey confirms that snuff is currently more prevalent than chewing tobacco.

Third, one-time smokeless tobacco users were combined with daily heavy smokeless tobacco users. Although the authors address this in the Discussion, their argument does not support their inferences. They use data from a previous report suggesting that, among smokeless tobacco users who report any lifetime use, 26 percent use it daily (6). The authors concluded that "many" of the smokeless tobacco users in this study used smokeless tobacco regularly. We do not agree with the notion that one out of four is "many" and contend that this study does not adequately assess the risk associated with the meaningful exposure of daily smokeless tobacco use.

The most important issue is that the public will be potentially misled by a study suggesting that smokeless tobacco is harmless, a conclusion that cannot be drawn based upon the data.

REFERENCES

REFERENCES

  1. Accortt NA, Waterbor JW, Beall C, et al. Chronic disease mortality in a cohort of smokeless tobacco users. Am J Epidemiol 2002;156:730–7.[Abstract/Free Full Text]
  2. Giovino GA, Schooley MW, Zhu BP, et al. Surveillance for selected tobacco-use behaviors—United States, 1900–1994. MMWR CDC Surveill Summ 1994;43:1–43.[Medline]
  3. Shapiro JA, Jacobs EJ, Thun MJ. Cigar smoking in men and risk of death from tobacco-related cancers. J Natl Cancer Inst 2000;92:333–7.[Abstract/Free Full Text]
  4. Nelson DE, Davis RM, Chrismon JH, et al. Pipe smoking in the United States, 1965–1991: prevalence and attributable mortality. Prev Med 1996;25:91–9.[CrossRef][ISI][Medline]
  5. US Department of Health and Human Services. The health consequences of using smokeless tobacco: a report of the Advisory Committee to the Surgeon General. Bethesda, MD: Public Health Service, US Department of Health and Human Services, 1986. (NIH publication no. 86-2874).
  6. Rouse B. Epidemiology of smokeless tobacco use: a national study. Natl Cancer Inst Monogr 1989;8:29–33.




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