Vol. 41 Epidemiological Approaches to Heart Disease: The Framingham Study* THOMAS R. DAWBER, M.D., GILCIN F. MEADORS, M.D., M.P.H., AND FELIX E. MOORE, JR. National Heart Institute, National Institutes of Health, Public Health Service, Federal Security Agency, Washington, D. C. THE use of the word " epidemiology " cal diagnosis. Thus, today, the epidemi- and the concept of what epidemi- ological approach is used to explore ology as a discipline may encompass has certain relationships in health and disease varied widely since the days of Peter which, with present technological meth- Panum and John Snow. There are today ods, cannot be observed directly. In many differing definitions of the word, addition to the many studies of the infec- but nearly all workers in the field will tious diseases, there have been epi- agree on one element of the definition: demiological studies in the fields of The word " epidemiology " by etymology nutritional imbalance, metabolic dis- refers to the study of something " which orders, occupational hazards, accidents, is thrust upon the people." There are cancer, and rheumatic fever-to mention still some who insist that epidemiology only a few. deals only with epidemics of infectious In the field of cardiovascular diseases, diseases, but current usage suggests that studies using the epidemiological method most workers would now agree that epi- have led to findings of considerable prac- demiology deals with " the fundamental tical importance for prevention and questions as to where a given disease is treatment. Mention may be made, for found, when it thrives, where and when example, of the studies of nutritional it is not found . in other words it is diseases, such as beriberi, pellagra, and the ecology of disease " 1 without regard scurvy, and of the infectious diseases to whether the disease is believed to be such as syphilis, hemolytic streptococcal infectious. infections, and streptococcus viridans Frost gave an analytical definition bacteremia. Rubella and other virus when he wrote that epidemiology " in- diseases have been implicated as etio- cludes the orderly arrangement of facts logical factors in congenital malforma- into chains of inference which extend tions of the heart, but further epidemio- more or less beyond the bounds of direct logical study is still required to establish observation."2 His definition might be these relationships beyond the possibility called the essence of the " epidemiological of reasonable doubt.3 Even in rheumatic method " except for the fact that it has fever, where fundamental etiology is still been used by the physician since the obscure, epidemiological studies have time of Hippocrates to arrive at his clini- helped to demonstrate the relationship of streptococcal infection to subsequent rheumatic activity, and this has led to * Presented at a Joint Session of the Epidemiology, Health Officers, Medical Care, and Statistics Sections the adoption of control measures which of the American Public Health Association, at the show Seventy-eighth Annual Meeting in St. Louis, Mo., great promise:4 November 3, 1950. It should be pointed out, however, [279] 280 AMERICAN JOURNAL OF PUBLIC HEALTH March, 195f that except for rheumatic fever, the dis- At this point it is well to present in eases mentioned above account for only outline the principal considerations a very small proportion of morbidity or which guided the development of the mortality from cardiovascular disease. study, and led ultimately to its location Of the epidemiology of hypertensive or in Framingham, Mass. arteriosclerotic cardiovascular disease al- The study is focused on arteriosclerotic most nothing is known, although these and hypertensive cardiovascular disease, two account for the great bulk of deaths because these are the most important of from cardiovascular disease. The scanty the cardiovascular diseases and the least epidemiological knowledge of these dis- is known about their epidemiology. As a eases which does exist is based either on working hypothesis it is assumed that the study of mortality statistics, which these diseases do not each have a single in the investigation of long-term diseases cause (as is the case in most infectious are often not very revealing, or on clini- diseases), but that they are the result cal studies, which have the disadvantage of multiple causes which work slowly from the epidemiologist's point of view within the individual. It is recognized of being based on the study of those who that, for the most part, specific and un- already have the disease. Clearly, what ambiguous tests for precise diagnosis of is required is the epidemiological study the early stages of these diseases are- of these diseases based on populations of lacking. normal composition, including both the Based on these general considerations, sick and the well as they are found in the following research plan was devel- the community. oped. A group of randomly selected per- These facts have long been recognized. sons in the ages where arteriosclerotic- Sir James Mackenzie, one of the great and hypertensive cardiovascular disease pioneers in cardiology, over 30 years ago are known to develop is selected for began what was intended to be a long- study. Based on as complete a clinical term study of disease in the entire popu- examination as feasible, there are selected lation of the town of St. Andrews, out of this initial group those persons Scotland.5 Because of Mackenzie's re- who are free of definite signs of these tirement a few years after the start of diseases. These persons will be termed the study, it was never completed, how- the normals, and they will be observed ever, and since that time there have been over a period of years until a sizable no other attempts to study heart disease number are found to have acquired the- in a large population of normal composi- diseases. At that time a search is made tion over any long period of time. The for the factors which influenced the expense of such a study and the necessity development of disease in the one group of guaranteeing its operation for a span and not in the other. of many years puts it beyond the ca- As one by-product of this investigation pabilities of the individual investigator. it will also be possible to study the effi- If such a study is to be done, it is clear ciency of various diagnostic procedures that it must be carried out by the com- in finding heart disease or as indicators munity health agencies. In the light of of the subsequent development of heart this situation, and with the g'rowing disease. (These findings, of course, have interest in chronic diseases, the U. S. important bearing on the question of Public Health Service began in 1947 to including tests for heart disease in mass lay plans for setting up an epidemio- screening programs.) A second by-prod-- logical study of the cardiovascular dis- uct will be data on prevalence and eases in cooperation with state and local incidence of cardiovascular diseases. health agencies. With these aims set up, it was then Vol. 41 FRAMINGHAM STUDY 281 necessary to define the population on State Health Commissioner for Massa- which the study would be carried out. chusetts, offered to cooperate with the Ideally, perhaps, epidemiological investi- U. S. Public Health Service in setting up gations of cardiovascular disease should the study in that state, and after con- be set up in a number of widely separated sideration of a number of possible areas areas simultaneously, so that various the Town of Framingham was selected. racial and ethnic groups will be repre- Framingham, lying 21 miles west of sented, and a variety of geographic, Boston, is an industrial and trading socio-economic, and other environmental center of 28,000 population, and is al- factors can be considered. The results of most independent of Boston from the a study of a single area will have gen- standpoint of providing suburban resi- erality only in so far as the population dence for the city. As is true of New of the area is representative of some England towns, it includes not only the larger population. Many thousands of built-up business and residential areas persons should be included to allow for but also the outlying rural area within numerous axes of analysis, and it would the town limits. Other points of interest be profitable to follow a cohort of indi- are that Framingham has the town- viduals from birth to death. Because of meeting form of government and the the expense of examination and follow- people are accustomed to and well versed up, however, it is not practicable to carry in the group approach to their problems. on studies simultaneously in several It was in Framingham that the first com- areas, nor to observe more than a few munity study of tuberculosis was under- thousand persons for a limited number taken-a program sponsored by the of years. It was concluded, therefore, National Tuberculosis Association and that the study should be set up in a the Metropolitan Life Insurance Com- single area, and that coverage would pany, which began in 1917 and continued have to be limited to approximately successfully for six years.6 This latter 6,000 persons in a limited age range, who fact, together with an indication of would be observed for a period up to 20 interest in response to the initial ap- years. A town of 25,000 to 50,000 popu- proach influenced to some extent the lation will supply this number of adults, selection of the town. and it was felt that a town of this size The problems involved in setting up would be more desirable than a larger the study fell into four categories: pro- city for the type of community approach fessional, administrative, organizational, required to secure full co6peration and and technical, and all will be discussed coverage.