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U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE Public Health Service

The Health Consequences of SMOKING 1968 SUPPLEMENT TO THE 1967 Public H~alth S~rvic~ R~vi~w U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE Public Health-Service

Foreword Section1 5 (ct) (1) of Public Law 89-92, the Federal Cigarette Label- lug a~d Advertising Act, requires the Secretary of Health~ Educa- tion, a.nd ~Velfal'e to submi~ a.n annua.1 report, to the Congress 1968 Supplement to "concerning (A) current information on the health consequences of smoking and (B) sucll recommendations for legislation as he may deem appropriate." This 1968 Supplement to the 1967 Public Health Service Public Health Service Publication :No. 1696 review, "The Health Consequences of Smoki~xg", was prepared for the Secretary pursuant to this section. The Secretary's report was delivered to the Congress on July 1~ 1968. It is printed below. The information presented in the accompanying report, "The Health Con- sequences of Smoking, 1968 Supplement," confirms or strengthens the conclu- sions of two previous studies published by this Department--the 1964 :Report of the Surgeon General's Advisory Committee on Smoking and Health, and the 1967 Report on the Health Consequences of Smoking. These conclusions are that smoking is a serious health hazard in this counl:ry, Library of Congress Catalog No. 68-60025 one which is bringing about much unnecessary disease and death within our population. In the words of the 1964 Report, adequate remedial action is re- quired. In my opinion, the remedial action taken uutil now has no~ been adequate. I therefore recommend: 1. The warning statement required by the :Federal Cigarette Labeling and Advertisiug Act should be s'trengthened. This Department would support the wording recommended last year by the :~ederal Trade Commission, or a suitable paraphrase of the wording.* 2. This warning should be required to be placed not only on the cigarette package but on cigarette vending machines and in all advertisements. 3. Levels of "tar" and nicotine in cigarette smoke should be published on cigarette packages, on cigarette vending machines, and in all advertisements. Authorization is also needed to make it possible to add other harmful agent~ to this listing. 4. Appropriations should be made to the Federal Trade Commission to pe~aait the (.'ommission to test all cigarette brands on a quarterly basis for "tar" and nicotine and other harmful agents in cigarette smoke. Secretary. For ~]e by the Supcr~nte~udent ofDocument~, O,S. Government Printing O~ce * The wording recommended by the Federal Trade Commission (Report to W~hi~g~o,, D.C. ~o4o~. Prlcn SS c¢~t, Congress, Juim 30, 1967) was "Warning : Cigarette Smoking is Dangerous to Health and May Cause Death from Cancer and Other Diseases."

Preface The following pag'es provide a review of current information on the ~_~ health consequences o~ smoking. As will be seen, the evidence at~t~ting ~ to the h~rmful effect of smoking on health h~ condiment to mount ~ during the p~st year, with new research find, il~gs col~rming the clini- ~ ~'al~ e.xl)er~me~ca~~ a~d epidemiologiea] relationships bet~veen tobacco - smoking aud ma.ny forms of illn~s related to it. Tlm convergence of research findings continues wit]~out sub~ant:iul negative scientific e~'idence, h~ew considerations are presented concerning some bio- mechanism involved in the pathogenesis of cardiovascular and bron- chopulmonary diseases. This 1968 Supplemental Report reviews fhe recent research literature on c~rd~ovascu]a~" d~e~ chronic bronchopu]mona~T disease and can- cer that has become ~vuil~ble s~nce Tl~e gea~th ~owsegue~ces of Smolc- ing~ A Pub~iv Health Service Review: 1967 was published. This publication in turn was a review of the research literature which had appeared in the 3~ years since the Surgeon General's Advisory Com- mittee issued ~ts monumental report in 1964. The current research findin~ should be considered in the perspe~i~e of the research evi- den~ previously presented ~n the 196~ a~d 1967 reports. Proble~ cre~ted by ~ig~tte smoking haw made this ~ difficult health issu~ Effective prevel~tive programs must be created if we ~re to meet smoking's gr~ve challenge to truman health succe~fully ~nd reduce ~he burden of suffering and ~onomic loss involved.

ENDICOTT, KENNET~ ~[., M.D.--Director, National Cancer Institnte, National Institutes of Health, Bethesda, Md. EPSTEIN, FREDERICK H., M.D.--Professor of epidemiology, Department of Epidemiology, University of Michigan, School of Public Health, Ann Arbor, Mich. FALK, HANS L., Ph. D.--Associate scientific director for carcinogenesis etiology, National Cancer Institute, National Institutes of Health, Bethe~da Bid. Acknowledgments FA~,,E~ EMMANUEL, M.D., Ph. D.--Professor and chairman, Departmen~ of Pathology, University of Pittsburgh, Pittsbnrgh, Pa. The National Cle~ringhouse for Smoking and Hea.lth, D~i61 Horn, Fz~zs, BEN~,',MIN G., Jr., M.D.--Professor, Department of Physiology, Harvard Ph. D., Director, was responsible for the preparation of this report; School of Public Health, Harvard Univer.~ity, Boston, Mass. Albert C. Ko]bye, Jr., M.D., M.P.H., LL.B., was senior editor and Fox, S,~.MUE~. M., III, M.D.--Chief, Heart Disease and Stroke C~ntrol Program, David G. We~ber, M.D., was staff director. National Center for Chronic Disease Control, U.S.P.H.S., Arlington, Va. FREDEI~.IOKS0N, DONALD S,, M.D.--Chief, Laboratory of Molecular Disease, Na- The p~vf~ssional staff of the National Clea.ringhou~ for Smoking .tional Heart Institute, National Institutes of Health, Bethesd,n, Bid. and He,~lth owes a debt of grat.itude to the ma.~y exl~e~ in the scien- F~o.~, A~THUg H., M.D.--Heart Disease aud Stroke Control Program, National tifiC and technical fields, both in and outside of the govermuent who Center for Chronic Disease Control, U.S.P.H.S., Applied Physiology Labora- have provided much ad~,ice and assistance. Their contributions are tor~, Georgetown University, Washington, D.O. gratefully ~clmowledg~d. GELLER, H,~aVEY--0hief, Operational Studies Section, Cancer C~ntrol Program, Special thanks are due the following: National Center for C'hr~nic Disease Control, U.S.P.H.S., Arlington, Va. Gr~r~soH~, AL~.~N, Ph. D.--Johns Hopkins University, School of Public Health, ~.r~n~eH, 0sc~, M.D.~Senior medical in~te~tigator, Veterans Administration Bal.Hmore, Hospital, East0range, N. $. GUDB~AtlNAs0N, SIG.~V~DU~, Ph. D.~Department of Medicine, Wayne State A~s, S~HEr~ M., M.D.--Director, Cardiopulmonary Laboratory, Saint Vin- University, Detroit, Mich. cent's Hospital and Medical Center of New York, New York, N.Y. H~,M~0ND, E. CuviEr, Sc. D.~Vice president, epidemiology and statistical re- B~.ss% S~Mv~_~, M.D.~Director, Division of C~rdiology, Philadelphia General search, American Cancer Society, New York, N.¥. Hospital, Philadelphia, Pa. Hsss, CX$HEaINE B., M.D.--Assistant to the chief, ~ancer Control Program, Silo, RIoH~a~ ~., M.D.--Professor and chairman, Departa~ent of Medicine, National Conter for Chronic Disease Control, U.S.P.H.S., Arlington, Va. "Wayne State University, Detroit, Mich. HI,GINS, I.T.T., M.D., M.R.C.P.~Professor, Department of Epidemlology, Uni- B0CK, FI~ED G., Ph. D.~Director, Orchard Park Laboratories, Roswell Park versity of Michigan, School of Public Health, Ann Arbor, Mich. Memorial Institute, Orchard Park, N.Y. HOFFMANN, DIEWaIcH, Ph. D.--Associate member, Environmental Carcinogene- BOEI~TH, ROBEaT, Ph.D., M.D.--National Heart Institute, National Institutes of sis, Sloan-Kettering Institute for 0ancer Research, New York, N.Y. Health, Bethesda, Md. IMBODEN, C~Ncs A., Jr., M.D.--Division of Regional Medical Programs, Na. Bom~, Ho~sIs, M.D.~Clinical investigator, Veterans Administration Hospital, tional Institutes of Health, Bethesda, Md. Denver, Colo. ISH~I, KANF.0, M.D.--Chief, Serology Division, National Cancer Center, Research BRAUNWALD, EUGENE, M.D.--Department of Medicine, University of 0alifornia Institute, Tokyo, Japan. ~anDiego, San Diego, Calif. KANNEL, WISL~,~M B., M.D.~Medical ~director, Heart Disease Epidemiology BRU~N~,'TTI, IDA L.~Health educator, Adult Heart-Preventive Programs Sec- Study, National Hear~ Institute, National Institutes of Health, Framingham, tion, Heart Disease and Stroke Control Program, Nation.al Center for Chronic Mass. Disease Control, U.S.P.H.S., Arlington, Ya. KELS~, ANDrCEW Z., D.M.D., M.P.H.~Chief, Research in Geographic Epidemi- GH,~nwIcK, DON,~L~ R., M.D.~Director, National Center for Chronic Disease ology Research Service, Veterans Administration Cen.tval Office, Department Control, U.S.P.H.S., Arlington, Ya. of BIedicine and Surgery, Washington, D.C. GH~c~', Ih~ITTON, Ph.D., Sc. D.--Director, Johnson Research Foundation, Chair- K~NNS~, H,~aaIs M', M.D.--Medical consultant, Heart Disease and Stroke Con- man, Department of Biophysics and Physical Blochemist~w, School of Medi- trol Program, National Center for Chronic Disease Control, U.S.P.H.S., Arling- c|ne, University of Pennsylvania, Philadelphia, Pa. ton, Va. COO~'E|¢, Tm.:o~om..', M.D.--l)iret.tor, National IIeart Institnte, Natioual Instit||tes KmtS]~I~UAM, ALFREIL hI.D.~Asslstant chh,f, Division of Cardiology, PhiladelI~hia of Iit~||flb Betbesda, Md. Gener~il. Ilosp|t~|l, Philadellfl|ia, l'a. DoYs.~, Josm,~ T., M.D.--Professor of medicine, Albany Medical College, KOTIN, Pd~X~, M.D.--Director, Division of Environmental Health Silences, U.S. Albany, N.Y. P.H.S., Research Triangle Park, N.C. EDEREt~, FaED--Statistician, Biometric Research Branch, National Heart Insti- K~c~ov.z, Rxc~r~v~ A., M.D.~Director, Medical Chest Department and .t~te, Nation~t~ Institu.tes of Health, Bethesda, Bid. monary Function Laboratory, Charles F. Kettering Memorial Hospital, Ketter- E~XOT, R0nE~T S., BLD.~Assoeiate professor of medicine, Department of Medi- ing, Ohio. clue, Division o£ Cardiology, College of Medicine, University of Florida, LILIE~FELD, A~aa~,~M, M.D.--Professor and chairman, Department of Chronic Gainesville, Fla. Diseases, Johns Hopkins School of Hygiene and Public Health~ Baltimore, Md. vi vii

~-~oLEAn, ROSS, M.D.--Professor of medicine (pulmonary disease), Emery Uni- versity, School of Medicine, Atlanta, Ga. MCM~LAn, GAan,~a~ C., M.D.--National Heart Institute, National Institutes of Health, Bethesda, l~Y~a, JoHn S., M.D.--Professor and Chairman, Department of Neurology, College of Medicine, Wayne State University, Detroit, Mich. i~I00~E, GEO~0S E., M.D.--Director, Roswell Park Memorial Institute, Buffalo, Contents MOUNT, FIIANX ~V., 5I.D.--Acting chief, Chronic Respiratory Disease Control :Page 111 Program, National Center for Chronic Disease Control, U.S.P.H.S., Arlington, Foreword ............................................... Ya. Preface ................................................ v ~'IUIIPtIY, EDMOND A., hi.D., St. D.--Associate professor, University of Colorado vi l~Iedical Center, Medicine and Biostatistics, Denver, Colo. Acknowledgments ................... - .................... NADIgL, JAY A., ~I.D.--Cardiovascular Research Institute, University of California Part I. Current Information on the Health Cons3quences of l~Iedical Ceuter, San Francisco, Calif. Smoking ..................................... 1 ~)AYI'~'E, GERALn }I., 5I.D.--Chief, Adult tIeart-Preventive Programs Section, Highlights of the Report ..................... 3 Heart Disease and Stroke Control Program, National Center for Chronic Smoking and Overall h~[ortality ............... 5 Disease Control, U.S.I'.H.S., Arlington, Va. : Part II. Technical Reports on the Relationship of Smoking to PETERSON, WILLIAM: F., M.D.--Chief, Obstetrics and Gynecolog.v Service, USAF 11 Hospital, Andrews Air Force Base, WashingtoD, D.C. Specific Disease Categories ...................... P~,T'r¥, THOMAS L., M.D.--Assistant professor of medicine, l:nivt=rsity of Colorado Chapter 1. Smoking and Oardiovascular Diseases_ 13 Medical Center, Denver, Colo. Chapter 2. Smoking and Chronic Bronchopul- PVl~I, PRITPAL S., M.D.--Department of Medicine, Wayne State University Medical monary Diseases (Non-neoplastic) __ 63 School, Detroit, Mich. Chapter 3. Smoking and Cancer ............... 87 Q~'IINLAN, CARROL B., M.D.--Deputy chief, IIeart Dis(,ase and Stroke Control Pro- gram, National Center for Chronic Disease Control, U.S.I~.tI.S., Arlington, RoBz~s, Mo~wox--Chief, Program Statistics and Analysis Section, Heart Disease ' and Stroke Control Program, National Center for Chronic Disease Control, U.S.p.H.S., Arlington, Va. Ross, WZLL~A.~i L., M.D.--Chief, Cancer Control I'rogram, Natim;al Center for Chronic Disease Control, U.S.P.H.S., Arlington, Va. ScHAettTER, gosEPz.;--Statistician, Adult Heart Activities, Heart Disease and Stroke Control Program, National Center for Chronic Disease Control, U.S. P.H.S., Arlington, Va. SCHUMAn, LEONARD hi., 5LD.--Professor of epidemiology, University of Minne- sota, School of Public Health, hIinneapolis, Minn. STAI~ILER, JEREMIAII, M.D.~Chicago Board of Health, Health Research Founda- tion, Chicago, Ill. TI.IOM, THOMAS J.--Statistieian, Program Statistics aad Analysis Section, Heart Disease and Stroke Control Program, Natimml Center for Chronic Disease Control, U.S.P.H.S., Arlington, Va. ~'VESTURA, El)WIN E., M.D.--Heart Disease and Stroke Control Program, National Center for Chronic Disease Control, l'.H.l*.II.S., ('hief, Al~plied l~hysiolog.v Laboratory. Gcorgetown University, "Washington, D.C. ~,'~*'~'NI)ER, ERNEST L., 5l.D.--Associate member, Sl~}an-I~:t, tt(q.i~g Institute for Cancer Research, New York. N.Y. ZUKEL, ~rII.LIAM .]'., M.D.--Assistant Dire('lor for ('~fllahorative Sludies, National Hear~ Institute, Natioaal InstitDtes of IIealth, Bethesda, hid. The following proi'essiolml staff of tim National (:learinghouse for Smoking and IIealth contributed to the preparation of this rol)ort: Selwyn 5[. Waingrow~ Dorothy E. Green, Ph. I)., l~oberI S. I Iutchings~ l~ichard ~V. While, Emil ('orwin, aml Robert F. ('larke, Ph. ]). Special thanks are due Jennie 5[. Jennings and Donald R. Shopland. ' *oo VIII

PART I Current Information on the Health Consequences of • , Smoking

Highlights of The Report Previoui .findings repol~ed in 1967 indicate that cigarette smok~g is associated with an increas~ ~n overall mortality and morbidity and leads to ~ suSstantial exce~ of deaths ~n those people who smoke. In a.ddi~ion, e~']de~c~ herein presented shows that lif~ expectancy among young .men is reduced by an average of 8 years in "heavy" cigarette smokers~those who smoke over two packs a day~ and an average o~ 4 years in "light" cigarette smokers, those who smoke less than one-half pack per day. ~q.m, olcing a~d Ca~iovasc~da~ Disea.~'es Current physiological evidence~ in combinatio~ wi~h additional cpidcmiological evidenc% confirms previous findings and suggests ad- ditional biomechanisms whereby cigarette smoking can contrib~c to coronary hear~ disease. Cigarett~ smoking adversely affects tim inter- action between the demand of the heart ~or oxy~n and other nutrients and their supply. Some o~ tlm harmful cardiovascular eff~ts appear ¢o ~ r~verslble aKer cessation'o~.cigarette smoking. Because o~ the increasing convergence of epidemiologicul and physi- ological findings r~lating cigarette smoking to coronary heart dise~e, it is concluded that cigarette smoking can contribute to fl~e develop- ment o~ cardiovascular disease and particularly to death ~rom coro- nary hea~ disease. ~mo~ng and ~hr~nic 05str~wtive B~'onvho~mo~T Dise~es Additional pIwsiologicaI and epidemiologicul evidence confirms the previous findin~ that cigarette smoking is the most important cause o~ chronic non-neoplastic bronchopulmonary disease in the United Stut~. Cigarette smoking can adversely affect pulmonary function and disturb cardiopulmonary physiology. It is suggested that this can lead to curdiopulmonary diseas% notably pulmonary hypertension and cot pu]monale in those individuals who have sever~ cM'onic obstructive bronc]fitls,

o°mol~i~.~7 aqzd £ddifional evidence substantiates the previous findings that ciga- rett~ smoking is the main cause of lung cancer in men. Cigarette smok- ing is causally ~lated to lung cancer in women but accounts for u smaller propolgion of cases than in men. Smoking is a signilican~ factor ~ tlm causation of cancer of the ]a~Tnx and in the development of can- Smoking and Overall cer o2 fl~e oral cavity. Furfimr epidemiological dat~ ~rengthea the ~s~iatioa o~ cigarette smoking w~th cancer o~ the bladder and caner o~ the p~ncreas. The 1964 Advisory Committee's Report (3) clearly and em- phatically outlined the dangers of cigarette smoking to health. The conclusions of the Committee, as outlined in the 1967 Report (2), were as follows: CIGARETTE smoking is associated with a 70-percent increase in the age-specific death rates of males, and to a lesser extent with in- creased death rate of females. The total number of excess deaths causally related to cigarette smoking in the U.S. population cannot be accurately estimated. In view of the continuinK and mounting evidence from ma.ny sources, it is the ~ud~ment of the Committee that cigarette smoking contributes substan(ially to mortality from certain specific diseases and to the overall death rate. " In general, tlm greater the number of cigarettes smoked daily, the higher the d'eath rate: For men who smoke fewer than 10 cigarettes a day~ according to the seven prospective studies, ~-he death rate from all causes is about 40 percent higher than for nonsmokers, l%r those who smoke f~om 10 to 19 cigarettes a day, it is about 70 percent higher than for nonsmokers; for those who smoke t0 to ~9 a day, 90 percent higher, and for those who smoke 40 or more, it is 1~0 percent higher. Cigarette smokers who stopped smoking before enrolling in the seven studies have a death rate about 40 percent higher than non- smokers, as against 70 percent highe.r for current cigarette smokers. l~{en who began smoking before age ~0 have a substantially higher de,~th rate than those who began after age ~5. Compared with non- smokers, the mortality risk of cizarette smokers, after adiustmenb for differences in age, increases with duration of smoking (number of .years ), and is hia'her~ in. thos~ who sto~ed__ after age 55 than for those who stopped at an earher 'age. In two studies which recorded the degree of inhalation., the mor- tality ratio for a ~-ea amount of smoking was greater for inhalers than for noninhalers. The ratio of death rates of smokers to that of nonsmokers is highest at the earlier ages (40-50) represented in these studies, and declines with increasing age. Possible relationships of death rates to other forms of tobacco use were also investigated * * *. The death rates for men smoking less than 5 cigars • day are about the same as for nonsmokers. For men smoking more than 5 cigars daily, de~th rates are slightly higher. There is some indication that thes~ higher death rates occur primarily

in men who have beeu smoking more than 30 years and who inhale the ward trend is reported in lung cancer death rates for the entire group smoke to some degree. The death rates for pipe smokers are little (mnokers, ex-smokers, and those who never smoked, combined) along if at. all hi~her than for nonsmokers, even for meu who smoke 10 or with. a very ~sharp reduction iu cigarette smoking by the phys, ici~? more pipefuls a day and for men who have smoked pipes more than is the best available example of a controlled cessation experiment; w~rn 30 years, reduction of risks resulting from reduction of smokiug. The fiudin~ of this report support the view that epidemiological data showing In fact, the Committee's concern was of such an immediate nature lower death rates amoug former smoket-s than mnong continuing that they recommended : "* * * appropriate remedial action." smokers cannot be dismissed as due to selective bias and that the bent- The 1967 report reviewed the literature of the ,3!.6 years subsequeut fits of Mving up smoking have probal)ly been understated. to the 1964 report and found no evidence to refute the conclusions of 5. Ci~garette smokers have higher rates of disability than nonsmok- ers, whether measured by days lost from work among the employed the latter, population, by days speut ill in bed, or by the most general measure Additional evidence was given which clarified some of the patho- --days of "restricted activity'? due to illuess or injury. Data from the biomechanisms of the diseases associated with smelting. The fiudiu~ ~ National Ilealth Survey provide a. base for estimating that in 1 year of the 1964 report were strengthened and some new ones stated. New i in the United States an additionid 77 million man-days were lost from d,at.~ on the general mortality and morbidity associated with smoking I work, an additional 88 million'man-days were spent ill in bed, and were presented. The highlights of the 1967 report are given below: . an additional 806 million man-days of restricted activity were experi- 1. The previous conclusions with respect to the association between ' enced because cigarette smokers have higher disability rates than non- smelting and mortality are both confirmed and strenNhened by the smokers. For men age 45 to 6£ ~8 percent of the disabilit~ days ex- recent, reports. The added period of followup and aualYsis of deaths perienced represent the excess associated with cigarette smoking. of nonrespondents as well as of respondents in the Do~n Study sug- In the 1967 Report the following questions were emphasized: tests that the earlier reports may have uuderstated the relat!dnship. 1. How much mortality and excess disability are associated with ~. More information is now available for specific age groups than smoking? ~PnreViously. A eomparisou of three ways of measuring the relationship . dicates that cigarette smokin~ is m})st important kmong men aged : ~. How much of this early mortality axd excess disability would ~5 to 54 both in terms of mortality ratios and excess deaths expressed not have occurred if people had not taken up cigarette smoking as a percentage of total deaths. Nevertheless, although both of these : 3. How much of this early mortality and excess disability could be measures decl]ne witl~ advancing a~'e, the increment added to the death " rate, which reflects one's personal chances of being affected, continues averted by the cessation or reduction of cigarette smoking? to increase with age. For men between the ages of 35 and 59, the : 4:. What are the biomechanisms whereby these effects take place excess deaths among curreut cigarette smokers attempt for one out ~ and what are the critical factors in these mechanisms of every three deaths at these ages. For women, with their lower over- The problem of how best. to measure the relationship between smok- ~11 exposure to cigarettes, the comparable figure is about one death out of every 14 at ages 35 to 59. I ing and mortality was presented by three meaningful measures of 3. Women who smoke cigarettes show significantly elevated death i comparison: r~tes over those who have neve,r, smok,e~d regularly. The magnitude of the relation~!~ip varies with se~ eral mcasnres of dosage. B~:'and large i~ 1. Mortality tlatios: Obtained by dividing the death rate for a elas- the same m erall relationships between smoking and m~rtality are sification of smokers by the death rate of a comparable group of no_n- observed for women as had previously been report,e,d for men, l;ut at. smokers * * * A mortality ratio has been considered to reflect the a lower level. Not. ouly are the deatl{ rates for mt n who have never degree to which a classification variable identifies or may account for variations in death rates. As such, it is a measure of relati've risk which smoked regularly higher than those for women who have never smoked indicates the impoi~ance of that variable relative to uncontrolled vari- re~flarly, but the etfeet of smoking a.~ lneasured either by di fferences in aboles--an indicator of l~ote~tial biological signifiea.~we. death rates or by mortality ratios-is greater for men tl{an ~or women. ~. Differences in Mortality Rates: Obtained by subtracting from _At least part of this can be accounted for by the lower ¢xposure of the death rate for smokers, the death rate of a comparable group of female cigarette smokers whether measured l~y number of cigarettes, nonsmokers * * *. This measure reflects the added probability of &lration of smoking, or degree of inhalation. " death in a 1-year period for the smoker over that for the nonsmoker. 4. Previous findings on the lower death rates amoug those who have As such it is a measure of personal health signifieanee, a means for discontinued cigarette smoking are confirmed and stren~hened by the the individual to estimate the added risk to which he is exposed. aclditional data reviewed. Kahn's analysis of ex-smokers in the U.S. 3. Excess Deaths: Obtained by subtracting from the number of veterans study--controlling for age at which they began smoking, deaths occurring in a group of smokers, the number of deaths which amount smoked, and current age ..reveals a dowuward trend in risk would have occurred ~'} that group of smokers had experienced the relative to those who continued to smoke as the duration of time dis- same mortality rates as a comparable group of nonsmokers. In the continued increases. The British physician study, in which a down- example which follows this has been reported as a percentage of all 3~5-181 0--08 2