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'Risk Factors' and Heart Disease
From: Cambridge University Press
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Robert A. Aronowitz |
EDITOR'S INTRODUCTION |
The notion that diet, exercise and lifestyle have an important bearing on susceptibility to heart disease has become commonplace. Yet, the idea of risk factors in heart health is a relatively recent development, and one that that is now largely unquestioned. By making the assumptions explicit, Dr Robert A. Aronowitz hopes to open them to healthy debate and analysis. In this extract from his book, Making Sense of Illness, he looks at the emergence of our knowledge of the role of risk factors in heart disease. |
 s late as the early 1950s, many researchers and clinicians believed that coronary heart disease (CHD) was a chronic, degenerative disease, a particular way of aging that did not lend itself to specific, preventive measures. For example the Commonwealth Fund Commission on Chronic Illness in 1957 concluded that atherosclerosis was "not preventable at the present time." Writing in 1976, Thomas Dawber and William Kannel, the longtime leader of the Framingham study, an epidemiological project that began in the late 1940s and that ushered in the risk factor era as much as any specific event, recollected that prior to that study "atherosclerosis was considered an 'aging process' and that people who tried to seriously investigate it were part of H. L. Mencken's 'cult of hope,' who strive to find solutions to insoluble problems" (Circulation 44, 4, p. 553). |
Then and now
In contrast to this fatalistic view of CHD, contemporary approaches stress that CHD is preventable by identifying and intervening in any number of modifiable risks such as smoking, high blood pressure and high cholesterol level. Moreover, contemporary biomedical investigators are no longer content to study only those factors traditionally understood to be modifiable. Nothing could be further from the older conception of CHD as an inevitable degenerative process than the contemporary race to identify--and perhaps manipulate--the "gene" for CHD. |
Although the case finding paradigm in which the general population was screened to find individuals with heart disease was sometimes promoted by analogy to tuberculosis in the first decades of the century, no major cardiac control campaigns were launched prior to the risk factor era. Unlike the earlier tuberculosis model of prevention, which focused on identifying individuals who either did not know they had disease or did not seek medical attention, risk-factor-based public health practices have aimed to identify individuals who are at risk for the disease. The distinction is important because, according to risk factor logic, everyone is potentially at some risk, suggesting a rationale for screening whole populations, a formula for mass behavioral change, and a new way for individuals to understand their responsibility for, and contribution to, disease. |
While angina pectoris and CHD were not the focus of major prevention efforts in the first half of the twentieth century, there was a great deal of speculation about individual predisposition and life course contribution to disease. Although some of the influences cited by observers as predisposing the individual to angina pectoris in the early decades of this century--other medical conditions such as diabetes mellitus, worry and stress, habits and behavioral choices such as smoking--we now think of as risk factors for CHD, these influences arose in a different context and thus had a different meaning. These predisposing influences were discovered and accepted on the basis of clinical experience. The seemingly "correct" associations from today's vantage point were just a few of the many observations drawn from clinical practice, none of which were subjected to rigorous epidemiological or clinical validation. Even the wisest clinician--then or now--could not see many of these gradual, complex, and subtle interactions in everyday practice. Thus, creating a consensus about a select number of correct associations was impossible in the earlier era even if there had been a desire to create one. |
In contrast, risk factors have been legitimated by large-scale epidemiological studies. Consensus has been reached (although not without controversy) that a small set of clearly identified factors contribute independently to CHD risk. This process has been aided by the determined efforts of national organizations such as the American Heart Association to create panels of experts who review this literature and make clinical and public policy recommendations. |
In the earlier era, predisposing or inciting causes were often listed as names of different types of angina pectoris, for example, alcohol angina. This speculative classification based on the individual's contribution to disease was a practice that continued through the late 1950s. It was perhaps easier to identify how people's individual circumstances led to their pain and therefore identify many different types of angina because angina pectoris was defined as a particular chest pain syndrome rather than an anatomic abnormality. |
The situation today
In contrast, today's system of classification does not distinguish different types of angina pectoris and CHD on the basis of what the individual contributes to disease. However, contemporary risk factors are often talked about as diseases in their own right, especially hypertension and hyperlipidemia, defined by (often arbitrary) statistical cutoffs. The meaning of such factors to particular patients and their clinicians lies solely in their probability of contributing to disease. The specificity of the diagnosis derives from the ability of the clinician or laboratory to assign a precise number to blood pressure or serum cholesterol level and the epidemiologist to correlate that number with the probability of developing disease. Such probabilistic reasoning was not part of most physician and patient thinking about the etiology and prevention of CHD in the pre-risk-factor era, although it was already prominent among actuaries who helped life insurance companies predict risk and set premiums early in the century. |
Clinicians in the pre-risk-factor era used knowledge about an individual's predisposition to frame diagnostic and prognostic information in a flexible manner appropriate for the individual, as well as the disease. They employed commonsense frameworks to understand the interaction and relative importance of various contributing influences. One clinician, for example, reasoned typically that tobacco might not be a primary cause of heart disease but a marker for the kind of personality predisposed to the disease, writing, "There is some indication that very heavy smokers are predisposed to coronary disease, but heavy smoking may be simply a demonstration of temperament and evidence of the tension of the individual who develops coronary disease" (W. G. Smillie, Preventative Medicine and Public Health, 2nd edn, 1954, p. 437). Common sense also meant finding reasons why habits that were prevalent among physicians and magazine editors of the day might not be so bad. A 1957 Time article on scientific progress in CHD reassuringly reported that "tobacco is no longer banned in all cases--there is little point in forbidding a tense patient to smoke a little, if it serves to relax him ... if one or two drinks a day serve to relax an otherwise apprehensive person, it would be unwise to prohibit them" ("Angina then and now," Time 69, Jan 7, 1957, pp. 69-70). Physicians and patients shared values and beliefs that allowed both groups to understand and manipulate questions about the individual's responsibility for CHD. In contrast, any connection between contemporary risk factor insights and widely held attitudes and beliefs about responsibility for disease is generally understood to be accidental. Contemporary risk factor practices are based or are believed to be based on objective and value-free epidemiological and clinical studies, not shared values or insights from the clinical care of individual patients. Risk factor knowledge is individualized according to quantitative parameters such as the degree of hypertension and the number of pack-years of cigarettes smoked, not according to the clinician's gestalt of his or her patient. In fact, guidelines promoted by national organizations for the screening and treatment of hypercholesterolemia leave little room for the individual physician and patient to negotiate. Intervals for screening, cutoffs for different degrees of risk, and thresholds for starting medical treatment have been determined by consensus panels for the average patient. |
The form in which knowledge about individual predisposition and contribution to disease is expressed has changed greatly in the past half century. At the turn of the century William Osler described the typical angina pectoris patient in a narrative that combined historical, personal, genetic, and social details. In contrast, the preferred forms to express contemporary risk factor knowledge are complicated risk factor equations derived from the logistic regression analysis of large, epidemiological data sets. Using these equations, the late-twentieth-century physician might offer a quantitative estimate of the patient's risk of developing CHD from the patient's serum cholesterol and glucose levels, blood pressure, tobacco exposure, and family history. |
Prognosis
In the era before risk factors, perhaps the most important application of knowledge about individual predisposition and contribution to disease was to understand the patient's prognosis better. Prognosis was more important in the pre-risk-factor era partly because there were few if any clinical trials comparing a particular therapy to a placebo or comparing different therapies. Inasmuch as quite different therapies or temporizing might be considered by clinicians, educated guesses needed to be made about the consequences of such choices. Knowledge about prognosis was usually derived from general clinical experience, although there were some attempts to determine more systematically the results of long-term follow-up of patients. Such clinically derived prognostic knowledge could not and did not form the basis of large public health efforts at primary prevention of CHD; rather, it helped physicians make clinical decisions and frame their advice to patients. |
In contrast, risk factor knowledge today serves many functions besides prognosis. Risk factors serve as the basis for national efforts to prevent CHD through lifestyle change and therapy for abnormalities found by risk factor screening. Risk factor knowledge also guides government policy toward new drugs and food labeling. Insurance companies use risk factor data to compute the actuarial risk of individuals and populations in order to determine premiums. Precise quantitative relationships between risk factors and disease derived from epidemiological studies are used to predict disease prevalence and incidence in other populations. Such predictions are used to formulate health policy and plan new clinical studies (especially to determine appropriate sample size). In sum, risk factors are a central part of modern clinical, public health, and financial strategies for predicting and managing individual variation in disease predisposition and experience. |
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