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Etiology

Cigarette smoking caused half the deaths in male physician smokers

ACP J Club. 1995 Mar-April;122:48. doi:10.7326/ACPJC-1995-122-2-048


Source Citation

Doll R, Peto R, Wheatley K, Gray R, Sutherland I. Mortality in relation to smoking: 40 years' observations on male British doctors. BMJ. 1994 Oct 8;309:901-11.


Abstract

Objective

To examine the risk for death associated with smoking among British men.

Design

Cohort study with 40 years of follow-up.

Setting

Community-based study in the United Kingdom.

Participants

34 439 male physicians completed questionnaires on smoking habits in 1951; subsequent questionnaires were sent out in 1957, 1966, 1972, 1978, and 1990.

Assessment of risk factors

Smoking habit and age.

Main outcome measures

Causes of death were obtained from death certificates. Mortality rates, standardized for age and calendar period, were analyzed for 48 causes of death and were grouped by smoking habit. Actuarial survival tables were constructed.

Main results

For the 40-year period, deaths from 9 of the 17 types of cancer were related to smoking (P ≤ 0.05). Mortality from cancers of the upper respiratory sites, lung, and esophagus in men who smoked ≥ 25 cigarettes/d was at least 15 times that of men who did not smoke. Mortality from 14 of the 18 respiratory and vascular diseases was related to smoking (P ≤ 0.05), with chronic obstructive lung disease showing an association almost as strong as lung cancer. Of the vascular diseases, death from pulmonary heart disease was most strongly related to smoking, and only 2 examined categories (rheumatic heart disease and venous thrombosis) were not related to smoking. Absolute excess mortality from vascular diseases, mainly coronary heart disease, was greater than that attributed to all cancers. For middle age and early old age, the overall mortality was twice as great in men who continued to smoke as that in men who did not smoke. Men who stopped smoking at 35 years of age had the same survival pattern as those who had never smoked regularly. Men who stopped smoking at any later time were still at less risk for death than were men who continued to smoke. The death rates in men who smoked cigarettes were double those of men who did not smoke throughout middle age during 1951 to 1971 and were triple during 1971 to 1991.

Conclusions

Cigarette smoking was associated with increased risk for death from 25 causes of death: The greatest relative risk was related to respiratory neoplastic disease, chronic obstructive lung disease, and pulmonary heart disease, and the greatest absolute risk was related to coronary heart disease. In the cohort of 35-year-old male physicians who smoked, it was estimated that half of the deaths during the subsequent 35 years were attributed to smoking (40% mortality vs 20% mortality in men who did not smoke).

Sources of funding: Imperial Cancer Research Fund and Medical Research Council.

For article reprint: Professor R. Doll, Imperial Cancer Research Fund Cancer Studies Unit, Nuffield Department of Clinical Medicine, Radcliffe Infirmary, Oxford OX2 6HE, England, UK. FAX 44-1865-5588-17.


Commentary

Modest alcohol consumption decreased total mortality

We already know that smoking is bad for health and that alcohol can be. What, then, do these 2 studies add to our knowledge?

Doll has been observing the consequences of smoking in a cohort of male British physicians for more than 40 years. The first reports from this study (1) were among the most important health research findings in this century; we know what we know about the risks of smoking largely because of Doll's pioneering work. In this article, Doll and colleagues describe the second 20 years of follow-up. Because the study is based on unusually long and complete follow-up, it adds to our understanding of how the duration of smoking affects risk.

The authors show that risk increases with duration of smoking. If smokers stopped smoking before middle age, their pattern of risk did not differ from that of nonsmokers. The benefits of quitting persisted throughout life; even elderly persons who quit had a lower risk than those who did not. As with other studies, the burden of illness from smoking was enormous. For example, two thirds of the deaths in middle-aged smokers were attributable to smoking. These observations remind us of the powerful effects of smoking on health and the value of quitting at any age.

Smoking did not necessarily cause all the deaths associated with it. A limitation of this cohort study is that smokers may have differed from nonsmokers in other ways that may be related to the risk for death; except for age, these other factors were not considered in the analyses. Also, information about the cause of death recorded in death certificates may have been affected by the attending physician's belief about the risks of smoking—for example, by attributing sudden death to coronary disease or calling a cancer of undetermined origin lung cancer. The findings, however, are consistent with those of other studies, and we should behave as if most of the 25 causes of death that were associated with smoking are at least partly caused by it and could have been avoided if the person had not smoked or had quit. Actual cause of death is, however, of secondary importance because all-cause mortality was strongly correlated with smoking.

As for alcohol, we know from many studies that it is harmful. Alcohol causes life-threatening disease of nearly every body system (liver, nervous system, gastrointestinal tract, heart, and others), accidents, and some cancers. Evidence also suggests, however, that moderate drinking may protect against cardiovascular disease (2), perhaps by raising high-density lipoprotein levels (3), decreasing platelet aggregation, and causing favorable changes in coagulation. This study addresses the net effect, how it relates to the alcohol dose, and how it can be explained.

The authors show, as others have (4-6), that in a “U-shaped” dose-response curve, alcohol consumption is related to death, with lower death rates occurring in men consuming 1 to 2 drinks/d than in abstainers or heavier drinkers. The authors also present evidence that the overall curve is the sum of at least 2 different dose-response curves, one for causes of death believed (from other studies) to be from alcohol and the second for cardiovascular disease. With increased alcohol consumption, the alcohol-related death rate increases, but the number of cardiovascular-related deaths decreases (at lower levels of drinking).

The higher death rates among abstainers observed in this and other studies are controversial. It is an unattractive finding for clinicians who have seen so many patients suffering from alcohol addiction and its complications. The observation is also consistent with findings in some alcohol drinkers who stop drinking when they become ill. Doll and colleagues present evidence against this explanation, showing that the association between alcohol and death was at least as strong in men without previous disease as in those with it.

The findings have subsequently been shown to be generalizable to women and older men (7). On the basis of this and other information, clinicians probably should behave as if moderate alcohol intake is, on average, not just harmless but beneficial.

Robert H. Fletcher, MD, MSc
Harvard Medical SchoolBoston, Massachusetts, USA


References

1. Doll R, Hill AB. The mortality of doctors in relation to their smoking habits. A preliminary report. BMJ. 1954;1:1451-5.

2. Rimm EB, Giovannucci EL, Willett WC, et al. Prospective study of alcohol consumption and risk of coronary disease in men. Lancet. 1991;338:464-8.

3. Suh I, Shaten BJ, Cutler JA, Kuller LH. Alcohol use and mortality from coronary heart disease: the role of high-density lipoprotein cholesterol. The Multiple Risk Factor Intervention Trial Research Group. Ann Intern Med. 1992;116:881-7.

4. Marmot MG, Rose G, Shipley MJ, Thomas BJ. Alcohol and mortality: a U-shaped curve. Lancet. 1981;1:580-3.

5. Shaper AG, Wannamethee G, Walker M. Alcohol and mortality in British men: explaining the U-shaped curve.Lancet. 1988;2:1267-73.

6. Klatsky AL, Armstrong MA, Friedman GD. Alcohol and mortality. Ann Intern Med. 1992;117:646-54.

7. Thun MJ, Peto R, Lopez AD, et al. Alcohol consumption and mortality among middle-aged and elderly U.S. adults. N Engl J Med 1997;337:1705-14.