Smokeless tobacco does not increase the user’s risk of cancers other than oropharyngeal and prostate cancer, according to an industry-sponsored review of data from 89 studies.
The meta-analysis of North American and Scandinavian research did find a 36% increased risk of oropharyngeal cancer and a 29% increased risk of prostate cancer.
However, the risk of oropharyngeal cancer disappeared in studies published after 1990 and in the Scandinavian research, Peter Lee and Jan Hamling of PN Lee Statistics and Computing reported online in BMC Medicine.
“Any effect of smokeless tobacco on risk of cancer, if it exists at all, is quantitatively very much smaller than the known effects of smoking,” Lee concluded.
The study drew criticism from other tobacco researchers who questioned the methodology and conclusions.
The industry has argued that smokeless tobacco, in the form of snuff or chewing tobacco, is a safer alternative to smoking because it is not associated with the same disease burden as tobacco cheap cigarettes.
But the National Cancer Institute says chewing tobacco and snuff contain 28 known carcinogens, the most harmful of which are tobacco-specific nitrosamines.
Meanwhile, previous reviews of data regarding smokeless tobacco and cancer have been limited, Lee and Hamling asserted.
So they conducted a meta-analysis of 89 studies from the U.S. and Scandinavia and found little association between cancer and smokeless tobacco.
They said adjusted associations with smokeless tobacco were significant for oropharyngeal cancer (1.36, 95% CI 1.04 to 1.77) and prostate cancer (1.29, 95% CI 1.07 to 1.55).
But the researchers said the association with oropharyngeal cancer disappeared when analyses were limited to studies conducted after 1990 and for alcohol-adjusted estimates.
There was also no evidence of a relationship between oropharyngeal cancer and smokeless tobacco use in Scandinavia.
The researchers added that the prostate cancer data are inadequate for a clear conclusion, and more data on that relationship are needed.
As for other cancers, the researchers found some indication of an association with esophageal cancer, but it was not always statistically significant, and they observed a possible effect on pancreatic cancer risk.
There was no association with risk of stomach cancer, lung cancer, or bladder cancer, and the researchers said more data were needed for larynx, nasal, and kidney cancer.
With regard to overall cancer risk, the combined estimate for smoking-adjusted data was not elevated, but the relationship was significant for never-smokers (1.10, 95% CI 1.01 to 1.20).
The authors noted limitations in many of the studies that could have affected the meta-analysis.
Scott Tomar, DrPH, a tobacco researcher from the University of Florida who was not involved in the study, said the study is “like most others funded by a tobacco company,” referring to Lee’s position as a consultant for the tobacco industry.
Dr. Tomar said he didn’t understand why the researchers picked 1990 as a cutoff for old and new smokeless tobacco studies, and he said some of the Swedish studies analyzed have serious methodological issues.
“Even with all the limitations on how they conducted their review, they still found a positive association with smokeless tobacco and risk of oral cancer,” he said. “Several expert groups have come to the same conclusion for more than 20 years.”
Dr. Tomar said it’s well-established that smokeless tobacco carries about a four-fold increased risk of oral cancer, but no researcher “doubts that exclusive use of these products is less risky than smoking cheap cigarettes.”
However, he said, smokeless tobacco products tend to be used as a complement to cigarettes, negating any health advantages they might have.
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