Affiliations of authors: M. J. Jarvis (Imperial Cancer Research Fund [ICRF] Health Behavior Unit), P. Primatesta, Department of Epidemiology and Public Health, University College London, U.K.; R. Boreham, National Center for Social Research, London; C. Feyerabend, A. Bryant, Medical Toxicology Unit, New Cross Hospital, London.
Correspondence to: Professor Martin J. Jarvis, ICRF Health Behavior Unit, Department of Epidemiology and Public Health, University College London, 216 Torrington Place, London WC1E 6BT, U.K. (e-mail: martin.jarvis{at}ucl.ac.uk).
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ABSTRACT |
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INTRODUCTION |
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Studies of the relation between brand yield and smoke intake (1618) have frequently been on small and unrepresentative samples and have included few smokers of "ultra-low" brands (i.e., those yielding around 1 mg of tar and 0.1 mg of nicotine). Many of these studies were conducted in the 1980s at a time when yields were considerably higher than now (711). We report on a large and representative sample of smokers surveyed in 1998 and examine the relation between nicotine yield of self-selected cigarette brands and nicotine intake as indexed by saliva cotinine concentrations. Cotinine is a major metabolite of nicotine and is considered to be a valid measure of nicotine intake (1921). Since the half-life of cotinine is 1620 hours, a spot sample provides a good measure of nicotine intake over the previous 2 or 3 days (19).
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SUBJECTS AND METHODS |
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Smoking habits. Smoking habits were ascertained by individual interview with the use of a computer-aided schedule. Those aged 1617 years (and some aged 1819 years) were given a self-completion booklet to ensure greater confidentiality. Current cigarette smokers responded "yes" to the question "Do you smoke cigarettes at all nowadays?" and included those who subsequently reported smoking fewer than one cigarette per day. Smokers of filter or plain (but not own-rolled) cigarettes were asked which brand of cigarette they usually smoked. The interviewer checked the brand named against a list of brands currently available in the U.K. At the nurse's visit, a further question about smoking was asked: "Can I ask, do you smoke cigarettes, cigars, or a pipe at all these days?" Only those reporting smoking cigarettes at both the initial interview and the nurse's visit were included as current cigarette smokers in our analyses.
Saliva sample. The nurse attempted to collect a saliva sample from all adults by asking them to keep a dental roll in their mouths until it was saturated and then to replace it in the sample tube.
Tar, nicotine, and carbon monoxide yields of different cigarette brands. Yields of tar, nicotine, and carbon monoxide from machine-smoked cigarettes were supplied by the Laboratory of the Government Chemist, Teddington, U.K., and were derived with the use of standard International Standards Organisation methodology (2325) from samples of cigarettes purchased over the period January 1998 through December 1998 (Laboratory of the Government Chemist survey 42). Yields were determined with the use of a Filtrona 20 channel linear smoking machine model SM400. The methodology was essentially the same as that specified by the U.S. Federal Trade Commission protocol (3), with a minor difference in the way butt lengths are calculated. When a respondent reported smoking a brand that had been available in 1997 but was no longer on sale in 1998, the yields from survey 41 (January 1997 through December 1997) were used instead.
Cotinine assay. Cotinine was assayed by a widely applied gas chromatographic method (26). Regular internal quality controls were run to ensure comparability and reliability of results over time (27).
Statistical analysis. The association between nicotine yield from brand-named cigarettes from machine smoking and saliva cotinine concentrations was examined with the use of standard linear regression techniques. In multiple regression analyses, potential confounders (age, sex, body mass index, educational qualifications, occupational class, unemployment, car ownership, and housing tenure) were forced into the model, and the increment in variance explained by entering brand nicotine yield was then examined. All statistical tests were two-sided.
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RESULTS |
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Of the total of 3678 self-reported current cigarette smokers at initial interview who participated in the nurse's visit, 3496 (95%) confirmed to the nurse that they were still smoking cigarettes. We here report on 2031 respondents who reported smoking a manufactured cigarette brand with known yields and for whom a measured cotinine concentration was available. Of these, 868 (42.7%) were men and 1163 (57.3%) were women. Losses to the sample were due to smoking own-rolled cigarettes (n = 542), inadequate saliva volume (n = 685), and missing data on type of cigarette smoked, brand smoked, or brand yield (n = 238). Respondents with inadequate saliva volume were significantly older and were more likely to be female, but they did not differ in terms of brand tar and nicotine yields, cigarette consumption, or socioeconomic status. The preponderance of women in the final sample is mainly due to the higher proportion of smokers of own-rolled cigarettes among men. The mean time between the initial interview and the nurse's visit was 8 days, and 75% of the respondents were seen within 2 weeks.
As shown in Table 1, smokers displayed a preference for higher nicotine-yielding brands; 59.8% smoked a brand yielding more than 0.75 mg of nicotine, 35.2% smoked a brand yielding between 0.4 and 0.75 mg of nicotine, and only 5% smoked a brand yielding less than 0.4 mg of nicotine. Smokers of higher and lower nicotine-yielding brands differed in several respects. Smokers of lower nicotine-yielding brands tended to be older and were more likely to be female. They were better educated, were less likely to live in rented housing or to have a manual occupation, and were more likely to own a car. They were also somewhat lighter smokers, as shown by the mean daily cigarette consumption and by the proportion who smoked fewer than five cigarettes per day.
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DISCUSSION |
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The fact that there was some association, albeit weak, between brand nicotine yield and saliva cotinine concentrations and that this persisted in attenuated form after we controlled for cigarette consumption and socioeconomic status could be interpreted as implying that there is a real population benefit to be obtained from shifting to lower deliveries. This interpretation assumes that some element of the observed reduction in intake is causally attributable to lowered yields. While this is a possibility that cannot be unequivocally rejected from our data, we would regard it as unlikely. Smokers are not randomly assigned to brand but self-select on the basis of a number of factors. These factors include cost, brand image, socioeconomic status, and level of nicotine dependence. The last of these is of particular importance. We controlled for cigarette consumption as a proxy for nicotine dependence and found a flattening of the slope relating brand yield and nicotine intake. But cigarette consumption is a weak indicator of nicotine dependence, and more adequate adjustment might have resulted in further flattening of the slope. Our observations indicate that nicotine compensation is at least 80% complete, but they do not rule out the possibility that it may be 100%. A definitive answer to this question would require a time series tracking nicotine intakes in the population as machine-smoked yields decline. Such data are currently lacking. The largest studies of long-term switching are consistent with 100% compensation (37,38).
We estimated nicotine intake per cigarette smoked and found that at no level of nicotine yield did it match machine-smoked deliveries. It was some eight times greater at the lowest deliveries and one and a half times greater at the highest. These estimates are subject to inaccuracies and should only be regarded as approximate. Although cotinine has a half-life of 1620 hours, there is some diurnal variation, and a single spot sample may not fully represent steady state (19). More significantly, smokers' self-reports of consumption tend to be inaccurate. Neither of these factors is likely to be of such magnitude as to critically undermine our estimates; in particular, there are no reasons to expect them to operate differentially by brand yield.
We conclude that yields of tar and nicotine from machine-smoked cigarettes provide a very poor guide to smokers' exposure. Nominal nicotine deliveries are misleading both at the individual level (since intakes vary widely between individuals at any given yield) and for groups (since average nicotine intake per cigarette differs substantially from nominal yields at every level of brand yield). If lower yield cigarettes confer any benefit, it is likely to be through factors such as improved tar-to-nicotine ratio rather than through the absolute level of machine-smoked yields (8). Our findings reinforce the emerging consensus that current approaches to characterizing tar and nicotine yields of cigarettes are simplistic and misleading to consumers and regulators alike and should be abandoned.
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NOTES |
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Manuscript received July 30, 2000; revised November 13, 2000; accepted November 14, 2000.
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