A study recently published in the journal Cancer Epidemiology Biomarkers & Prevention found "similar exposures to the potent tobacco-specific carcinogen NNK in smokeless tobacco users and smokers." This is how The New York Times interpreted that finding:
Smokeless tobacco, the kind users put between cheek and gum, is one way to satisfy a craving for nicotine without offensive smoke. But a new study has found that it may be almost as effective as cigarettes in delivering nicotine and carcinogens….
Countering suggestions that smokeless tobacco might be a less harmful alternative for people unable to give up tobacco, the researchers wrote that smokeless tobacco is very risky, and should be discouraged.
Ignore the part about nicotine, which is a red herring: Nicotine is not a carcinogen, and effective nicotine delivery is an advantage, not a drawback, for a cigarette substitute. But the Times is suggesting that smokeless tobacco poses nearly as big a cancer risk as cigarettes, which would be cause for concern. The headline is even scarier: "Hazards: Smokeless Tobacco on Par With Cigarettes." In other words, using smokeless tobacco is no safer than smoking cigarettes.
In reality, the study dealt with a single carcinogen, not with the overall risks posed by smokeless tobacco vs. cigarettes. The researchers note that "cigarette smoke contains, in addition to NNK, multiple carcinogenic combustion products which are not present, or present in only low amounts, in smokeless tobacco." (They also note that Swedish-style smokeless tobacco, which is increasingly available in the U.S., contains about half the NNK of the traditional American brands used by the subjects in the study.) They never say the hazards of smokeless tobacco are "on par" with the hazards of cigarettes, or anything like that. In fact, that assertion in the Times headline is contradicted by the article under the headline, which quotes the study's lead author, University of Minnesota researcher Stephen Hecht, as saying (emphasis added):
The main message of this study is that smokeless tobacco cannot be regarded as safe, because it delivers just as much of one of the carcinogens in cigarette smoke as cigarettes do. While it may be safer than cigarettes, it is not nearly safe enough.
No one who recommends smokeless tobacco as a harm-reducing alternative to cigarettes says it's completely safe—only that it's much safer, as you might surmise from the lack of combustion products. Hecht himself does not dispute this fact, which has been confirmed by studies comparing disease rates among cigarette smokers and smokeless tobacco users. When he asserts that smokeless tobacco "is not nearly safe enough," he is not stating a scientific fact; he is making a value judgment.
The journal article likewise mixes data with moralism. "NNK exposure in smokeless tobacco users as shown in this study presents an unacceptable risk and should not be encouraged," Hecht and his colleagues declare. Unacceptable to whom? This judgment should be left to individual consumers, with the scientist's role limited to researching and reporting the risks. In Hecht's view, perhaps, no risk is acceptable, but the people whose health is at stake may disagree.
[Thanks to Brad Rodu for the tip.]