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CONTROVERSY Lung cancer and the 'safer' cigarette PETER N LEE MA Consultant in Statistics and Honorary Research Fellow, Divison of Epidemiology, Institute of Cancer Research, London years ago, when the evidence relating cigarette smoking to lung ~cer first started to appear, nearly all British smokers Smoked unripped (plain) Narettes with a tar yield of Today, more than of cigarettes smoked have and average tar yields are 15rag. Even the tar yields cigarettes have declined ~y so that hardly any garettes nowadays are above le 'middle tar' (17 to 22rag) ~nge while 'low tar' (0 to 10mg) lter cigarettes have captured rare than 15% of the market in ~last ten years. Similar trends ~e OCcurred in most developed .a developing countries (Lee, ~3). Although this suggests a ~uCtion in 1~ r'~neer c~uld l~u~(the tar ~ cffrcinouenic) it is ~h Considering a ~mber of .~ ~i,Rant~N points "sk of lung ~.~N~~ ~-$i~t, since the n dent on ~r is strongly depen ~--~d2tion of smoking (Doll and ~~, 1981), past exposure to ~~ettes is relevant, so that the ~~i~re of the effect of lower tar cigarettes is likely to take many years to emerge; early findings are likely to under- estimate the true benefit. Second, it does not necessarily follow that halving the dose of tar received by the smoker from each cigarette has the same effect on risk as halving the number of cigarettes smoked per day. Only for the. latter dose-response relationship is good evidence available. Third, changes in cigarette de- sign have resulted in chang6s in tar 'quality' as well as tar quanti- ty. Studies by Wynder and Hoff- man (1979) have shown that the mouse skin carcinogenicity of tar per unit dose has been steadily reducing. Fourth, reductions in risk will only be expected if smokers do not increase the number of cigarettes they smoke to 'com- pensate' for the reductions in nicotine yield that tended, at least until about ten years ago (Lee, 1976), to occur con- comitantly with the reductions in tar. Although consumption of .cigarettes per smoker has in- creased nationally, some studies suggest that changes in con- sumption are in fact essentially independent of changes in the tar/nicotine yield of the brand smoked (Garfinkel, 1979; Wald et al., 1980). Given that people currently smoking low tar cigarettes consume ten to 15% fewer cigarettes than middle tar smokers (Lee, 1983), the rise in consumption seems di~e to other causes such as lighter smokers giving up, or changes in price. Smokers may possibly compensate by altering the way they smoke their cigarettes, so the amount of tar they receive may bear little relation to the published yields, which are based on machine smoking under stan- dard conditions. A number of studies have investigated the relationship between machine nicotine yield and nicotine up- take. None of these studies is of the large, long-term 'within- smoker' type needed to provide reliable conclusions, and there is considerable variation in their findings, but all are consistent .with the theory of 'partial corn- September 1983 Vol. 227 1459 0 0

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CONTROVERSY that is a person smok- a reduced nicotine brand ~educes his nicotine intake, t~0ugh not proportionately by so large a factor. Russell et al. 11980) claimed support for the mnflicting viewpoint of corn- but re-analy- by Kozlowski et al. I1982) showed a clear trend to- wards reduced blood nicotine Nels in those smoking lower arettes. ~, now at the epidemiol- 0gy, four prospective and five ~ective studies have speci- investigated the relation- between lung cancer and smoked. Of the Separate comparisons made studies and sexes, 19 smokers of lower tar or clgarettes to have a lower lung cancer than smokers ~er tar or plain cigarettes, eXception being a non-sig- increase based on a re- small sample. Overall, reduction in mortal- 25 to 30%. It should be that in all these studies COmparison was between of the old high tar plain and smokers of filter of the middle or mid- tar group, typical of some vears ago. bach et a'l. (1979) com- legree of lung changes dying in 1955-60 dying in 1970-77 and the results show a marked differ- ence. If the lesions he studied are directly related to lung cancer, one cigarette of the past seems to be equivalent {o perhaps three or four modern cigarettes and life- time exposure to lower tar cigarettes may involve markedly tess risk than lifetime exposure to higher tar cigarettes. The changes in national mor- tality rates seem superficially rather unpromising, with male rates fairly static and female rates rising quickly. However, study of trends in total lung cancer rates gives a deceptive picture because in old men and in old and middle-aged women the average number of years smoking is sub- stantially greater now than for men and women of comparable age in earlier years. Since risk is related to the fourth or fifth power of duration of smoking, this increased duration will over- whelm any reduction in risk per cigarette smoked. To gain a more valid picture of potential benefits of tar re- ductions it is necessary to look at young and middle-aged men and young women, where changes in duration of smokir~g will not confound the picture. Over the last 20 years risk in men has fallen at all ages below 60 and has been halved in those aged 45 or less, and risk in women has fallen at ages below 45, and has been halved in the 30 to 34 age group. Although it is possible that reductions in air pollution fol- lowing the Clean Air Act are partly responsible, the magni- tude of the fall is too large to-be wholly due to this. Since average cigarette consumption per head has changed relatively little over the period, the trends are all consistent with tar reduction being the major factor. The fall in the lung cancer rate could be greater in years to come with cigarettes having even lower tar levels. References Auerbach O, Hammond EC, Garfinkel L. (1979): 'Changes in bronchial epithelium in relation to cigarette smoking 1955-1960 vs. 1970-1977". N Engl J Med. 300, 381-386. Doll R, Peto R. ( 1981 ): 'The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today', J Natl Cancer lnsr 66, 1191-1308. Garfinkel L. (1979): "Changes in the cigarette consumption of smokers in relation to changes in tar'nicotine content of cigarettes smoked', Am J Pub Hlth. 69, 1274-1276. Kozlowski LT, Frecker RC, Lei H. (1982): "Nicotine yields of cigarettes, plasma nico- tine in smokers and public health'. Prev Med, I1,240-244. Lee PN. (1976): Statistics of smoking in the United Kingdom. Tobacco Research Coun- cil Research Paper I, 7th ed. Lee PN. (1983): Lung cancer incidence and o'pe of cigarette smoked. Int Lung Cancer Update Conference, New Orleans. Russell MAH, Jarvis M, Iyer R, Feyerabend C. (1980): 'Relation of nicotine yield of cigarettes in blood nicotine level of smok- ers', Br Med J. 280, 972-976. Wald N J, Idle M, Boreham J, Bailey A. (1980): 'Inhaling habits among smokers of different types of cigarette', Thorax, 35, 925-928. Wynder EL, Hoffmann D. (1979): 'Tobacco and health: a societal challenge', New Engl J Med, 30t1, 854-903. 0 The Practitioner 1461 ~0 o 0~ o~ o o