Changes in the manufacturing processes of cigarettes have reduced the average tar rating per cigarette in the United States from 37 mg in 1950 to 13 mg in 1990. Consumer interest in low-tar cigarettes has resulted in the current availability of “low-tar” (8 to 14 mg) and “very-low-tar” (7 mg or less) cigarettes that are believed widely to pose less of a health risk than moderate-tar or high-tar brands. No large, long-term, prospective studies have examined the risk of lung cancer associated with low-tar cigarettes since the use of filters became widespread. Harris and colleagues used data from a large, national, prospective cancer prevention study to evaluate the risk of lung cancer in smokers who used cigarettes of different tar ratings.
More than one million adults 30 years or older were enrolled in the cancer prevention study in 1982. The researchers extracted data on 100,868 men and 124,270 women whose smoking status could be ascertained and who had no history of cancer, did not smoke pipes or cigars, and did not use chewing tobacco. Tar ratings were assigned to each participant based on the brand, size, presence or absence of menthol and filter, and number of cigarettes smoked at enrollment. All brands in the very-low-tar and low-tar groups were filtered, as were 99 percent of medium-tar (15 to 21 mg) brands. All high-tar brands (22 mg and higher) were unfiltered. The cause of death of participants as coded on death certificates was checked after six years to reduce mis-classification caused by quitting or change in smoking habits.
Persons who smoked high-tar brands were more likely to be black and less likely to take protective vitamins (i.e., vitamins A, C, and E) than other participants. They also reported lower educational achievements and were more likely to have nonprofessional occupations and to report possible occupational exposure to asbestos. Among participants who re-enrolled in a later cohort of the same study in 1992, those who had smoked low-tar cigarettes were more likely to have quit.
During the six years of follow-up, 2,622 men and 1,406 women died from cancers of the lung, bronchus, or trachea. The risk of lung cancer in smokers of low-tar or very-low-tar brands was indistinguishable from that in smokers of medium-tar brands. The risk of cancer was higher in those who smoked nonfiltered cigarettes, all of which were high-tar brands. Differences between the various brands persisted after adjustment for diet, occupation, medical history, and demographic characteristics. The lowest risk was in participants who quit smoking. Participants who quit smoking before 35 years of age had rates of cancer similar to rates in those who had never smoked.
The authors conclude that low-tar and medium-tar cigarettes are associated with identical risks of lung cancer. They believe that the relationship between tar levels and cancer risk must be nonlinear. Part of the explanation for their findings may be that smokers who switch to lower tar brands smoke more to maintain nicotine intake. This “compensatory smoking” may actually increase the dosage of toxic agent. They caution that switching to low-tar or very-low-tar cigarettes is not a sensible strategy to lower the risk of lung cancer.
editor’s note: In addition to the main message of the study—that switching from medium-tar to low-tar or very-low-tar cigarettes does not reduce the risk of lung cancer—this study is a powerful indictment of nonfiltered, high-tar cigarettes. Use of such brands has interesting patterns. For example, they comprise 20 percent of the Chinese market, 15 percent of the French market, and up to 20 percent of cigarettes sold in eastern Europe. By asking patients and observing public behavior, I have noticed the use of high-tar unfiltered brands by the groups mentioned in the study but also by some very young smokers, who are perhaps seeking the “macho” image associated with these dangerous brands. I know of no scientific evidence to validate my observations. Rates of smoking by young persons, especially women, are uncomfortably high. We need to use every patient visit to urge smokers to quit. From this study, the only benefit from the fallback position of “cutting down” appears to be in helping patients switch to filtered brands and in warning those who switch to low-tar brands about the dangers of smoking more cigarettes (compensatory smoking). Increasingly, it appears that quitting is the only way to reduce lung cancer risk.—a.d.w.