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Cigarette Smoking and Heart Disease The Tobacco Institute 1875 I Street, Northwest Washington, D.C. 20006 r 1983

, Cigarette Smoking and Heart Disease Introduction Eighteen years ago, the first Surgeon General's report reached a narrow and simple conclusiomabout smoking and heart disease*: "Male cigarette smokers_ have a higher death rate from coronary artery disease than non-smoking males, hut it is not clear that the association has causal significance." And: : "..mhe basic cause or causes of coronary heart disease are obscure..."1 Four years ago, in his 1979 report, the Surgeon General revised those conclusions: "...It can be concluded that smoking is causally related to coronary heart disease in the common sense of that idea and for the purposes of preventive medicine." *For the purpose of this paper, heart disease, coronary heart disease (('HD) and ischemic heart disease (TAD) are assumed to be synonymous. With the exception of direct quotation, the text uses "heart disease" only. i

And in another passage from the same report: "There is no reasonable doubt that cigarette smoking as a risk factor for...cardiovascular diseases has been proven."2 „ :. .. . . ,• . .,. . , _ _ ,x. Farly in 19R3, the Surgeon Ceneral is expected to issue a further report, devoted entirely to this subject. While we can speculate on what it may say, it seems proper to consider the sig- ,nificance and meaning of what has already been said and to indicate some of the subsequent contributions to scientific knowledge. The operative words in the previous conclusions are "associa- tion," "causally related," "cause" and "risk factor." A few com- ments on these are appropriate. , , On the first of those words, the 1964 Surgeon General's report said that "results of investigations must be considered to deter- mine first whether an association actually exists between an at- tribute or agent and a disease.... The causal significance of an association is a matter of judgment...."'1 ,, , _~. . ., . . , . That first report listed "consistency of the association" as a major criterion for such a judgment. As will be seen, there are many inconsistencies in results of investigations of smoking and heart dilsease. - The meaning of the phrase "causally related" is obscure. The iii

advisory committee that prepared the first SurgeoniGeneral's report said the meaning of "cause" was "discussed vigorously" in "debates" among the members, and that no member "used the word 'cause' inian absolute sense." The concept of "risk factor," perhaps the most gentle of these operative words in heart and other diseases, arose mainly from the Framingham study.. „ In iA49, the ti.5. Public Health Service began a close surveil- lance of more than 5y(D00 adult men and womeni in the community of Framingham,_Nassachusetts. Its major objective was to attempt to determine why individuals would develop evidence of heart disease. The Framingham researchers were to utilize direct observation and questionnaires to record the variables -- genetic traits, environ- mental characteristics, lifestyle and any other factors -- believed to be related to heart disease. They were to look at which of these variables were most common in those persons who did develop symptoms of heart disease. And they would attempt to determine statistically the relative importance of each in the occurrence of those symptoms. Those deemed important would be called "risk fac- tors,"n in the sense of common presence, not necessarily cause. The Frami'lngham study originally found "relationships" between heart disease and high serumicholesterol level, high blood pres- sure, obesity, low lung capacity and cigarette smoking.S' These were adjudged to be "risk factors." iii 1 i c ~

;-.;;,; ,-. Sixteen years later, the Framingham director, William Rannel, wrote that elevated bloo&pressure had been confirmed as the "dom- ,inant contributor" to heart disease in the study, hut that re- searchers were continuing to study the possible role of other "risk factors" in the development of heart disease.4 • .. . ,,. , _ 2 •"It must he remembered that by 1978 "risk factors" were no longer thought of merely as statistical "relationships"'by many in the medical community. In the years between the publication of -these two Framingharn reports, the role of high blood pressure in heart disease had been eLevated to "dominant contributor." The possible role of smoking as one "risk factor" among many was con- tinuing to be studied. In 1979, the author of a chapter in a medical textbook wrote that all known "risk factors"'taken together could account for • approximately 50 per cent of an individual's "risk" of developing heart disease in the United States. He added that important risk determinants remained to be discovered.5 ; _In 1979, the Surgeon (:eneraL's report said that relatively little was known about the mechanisms by which smoking was alleged to enhance atherosclerosis* or to increase the "risk" of heart attack. 1 . . .. • . li.. *Atherosclerosis, a form of arteriosclerosis, or thickening of the arteries is thought to be a principal factor in the development of heart disease. iv

The 1979 report also said~that smoking was not a necessary condition for atherosclerosis and heart attack, as these occur in '' nonsmokers, and that correlation is not synonymous withicausation. E , ;. It is generally recognized that statistical correlates derived~ from studies such as Framingham could identify certain characteris- tics that might possibly be related to aniindi'vidual's risk of de- veloping heart disease. Identification of so-called "risk factors" does not necessarily mean that the cause or causes of heart disease have been discovered. Although the 1979 report alleged smoking is "causally related" to heart disease in the common sense of the idea and for the pur- pose of preventive medicine, it suggested that additional research on mechanisms and on a more precise quantificationlof certain "risk factors" through epidemiological, studies* wa:s an important topic for medical science.9- . It would be difficult to find fault withithese suggestions for additional research. Without understanding of and'knowledge about disease mechanisms, there can he no certainty about what causes disease. In fact, the entire concept of "risk factors" might well deserve reevaluation by the medical and other scientific communities. *FpidemioDogy is a statistical science in which a group of people is studied to determine how oftenia disease occurs and what factors might be related to or associated with it. v

;.;The material that follows examines whether smoking has, in fact, been established scientifically as "causally related" to heart disease. It looks also at whether support for the claim that smoking is an important "risk factor" is as strong as some have suggested -- all in light of some of the scientific evidence presented mainly since 1979 and reviewed here. i ;r ~' V

11 Multiple Risk Factor Intervention Trial (MRFIT) ducing them in people presumably shoulid lower the mortality rate. If elevated cholesterol leve3,, hypertension* andicigarette smoking were "risk factors" for heart disease mortality„** then re- However, results'reported from recent intervention studies, such as AfRFIT, raise doubts as to whether the concept of "risk factors" carries the significance the medical community has ascribed to it , , . .. up to this time.'` The results of thi'ls "massive, expensive, and lengthy cli'~nical investigation termed 'Multiple Risk Factor Intervention Trial (MRFIT)"'6 were reported in the Journal of the Association in September 1982. American Medical vr. ' MRFIT was designed to test the effect of "risk factor" reduc- tion. tion. From among more than 300,000 volunteer American men,, 12,966 healthy but "high risk" subjects were assigned at random to one of two groups. "High risk" was determined by smoking history, serum cholesterol levels and diastolic blood pressure readings. *Hypertension is high blood pressure. **Mortality rate and death rate are used synonymously in this paper. - 1 - I y

Figure 1: Results from Multiple Risk Factor Intervention Trial (MRFIT) Percentage Reported Smoking at Beginning and End of Study 63a3"/a 63.5"ru 45.6°/ Beginning! G Death Rates per 1000 at 72 Months All Causes CV D' Including CHW' CHD E0 SI is Special Intervention group 'Cardiovascular Disease QUC Is Usual Care group~ "Coronary Heart Disease Source: From Multiple Risk Factor Intervention TriallResearch Group, "Multiple Risk Factor Intervention Trial: Risk Factor Changes and Mcrtality Results," JAMA 248(12): 1465-1477, Sept. 24; 1982 The special, intlervention group (SI) received special treatment for high blood pressure and physician counseling on smoking,and, diet. Members of the usual care group (UC) were left to their of six years the death rate from heart disease in the special intervention group would be reduced by 26.9 percent below that of the usual care group. regular sources of health care. Ilt was anticipated that at the end among the UC group, there was no significant difference in mortali- Although there was, after almost six years, a 46 percent re- duction in smoking among the SI group and a 29 percent reduction - 2 -