Getting To The Heart Of The 40-Year-Long Framingham Study

In 1948, a group of government researchers arrived in a small New England city to begin a long-term epidemiologic study of its residents. In the ensuing 42 years, their research has come to have considerable impact on health care in the United States. The project, the Framingham Heart Study, conducted by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health, has provided surveillance of the cardiac health of a randomly selected sample of men and women from Framingham, Mass. (see accompanying story). Its prospective nature has made it possible to define factors that may eventually lead to cardiovascular disease and, as a result, has triggered national health trends geared to intervene and reduce risk. As the data-collecting phase of the study draws to a close (funding is expected to expire in 1992), a look back over the past several decades reveals a body of valuable information that has had significant impact in cardiovascular disease research. "The Framingham Heart Study was created to study the incidence of coronary heart disease and the factors related to its development," explains William B. Kannel, former study director and currently professor of medicine and public health at Boston University School of Medicine. As such, the impact of this study has permeated every realm of cardiology. Perhaps the most important contribution of the study has been the identification of risk characteristics. In fact, a landmark study published in 1961 first coined the term "risk factor" (W.B. Kannel, et al., "Factors of risk in the development of coronary heart disease--six year follow-up experience; the Framingham Study," Annals of Internal Medicine, 55:33-50, 1961). Based on a six-year follow-up of the original cohort members, the study concluded, "combinations of these risk factors (hypertension, elevated serum cholesterol level, and left ventricular hypertrophy by electrocardiogram) were noted to augment further the risk of development of coronary heart disease." Framingham Findings On another front, Framingham data confirmed what researchers had suspected for years: Cigarette smoking is hazardous to the heart's health. A study published in The Journal of the American Medical Association (JAMA) in 1964 (J.T. Doyle, et al., "The relationship of cigarette smoking to coronary heart disease; the second report of the combined experience of the Albany, N.Y., and Framingham, Mass., studies," 190: 886-90) triggered the Surgeon General's later report warning against smoking. According to data compiled by the Philadelphia-based Institute for Scientific Information (ISI) in its Science Citation Index (SCI), this article is one of the 100 most cited articles published in JAMA between 1955 and 1983 (E. Garfield, JAMA, 257:52-9, 1987). Also among major JAMA publications stemming from the study is a 1970 article entitled "Epidemiologic assessment of the role of blood pressure in stroke" (W.B. Kannel, et al., 214:301-10, 1970). Evidence from the Framingham study concerning blood pressure found that elevated systolic pressure is just as dangerous to the cardiovascular system as high diastolic pressure. Furthermore, the study's findings have blurred the line between "normal" and "high" blood pressure. Evidence the researchers found suggested that the risk of stroke and heart disease rises even with a blood pressure level that is on the lower end of the "high" portion of the scale. The Framingham Heart Study also established high serum cholesterol levels as a risk factor, finding that cohort members who developed coronary disease usually had levels above 200 milligrams per deciliter. According to Kannel, the data were later "broadened to indict high levels of low-density lipoprotein as a risk factor of coronary disease." The danger levels defined by the Framingham study fueled the current federal guidelines for serum cholesterol levels. While the data gathered by Framingham Heart Study and other research projects provide undisputed evidence condemning high cholesterol levels, this portion of the study has caused controversy in the medical community. The study's results have led to a public health campaign to change the national diet. But Marvin Moser, a clinical professor of medicine at Yale University School of Medicine, is troubled with the way the data have been extrapolated. He says that often, in studies concerning cholesterol, only the extreme data are presented. "The cholesterol risk as defined by Framingham is not perfectly linear," says Moser. "While those with extremely high cholesterol levels are at high risk, the risks for those with middle-of-the-road levels flatten out considerably. "From a public health view, it is important to get the message out about risks. But public campaigns based on these data may overstate the problem, and worry those that should not be worried." Since it began, the Framingham Heart Study has spawned the publication of more than 480 papers (see accompanying table for a list of top papers from the Framingham study published during the period 1973 to 1988), and its investigators continue to produce about 12 papers a year. Kannel, a principal investigator from the beginning of the study, is the author or coauthor on more than 350 of these papers, garnering in excess of 7,400 citations between 1973 and 1988. He was one of the top 300 cited scientists between 1973 and 1984 (No. 249, with more than 6,250 citations for that period), according to the SCI database. Published findings from the Framingham study can be found at the heart of several research fronts, or specialty areas, as identified by ISI. Briefly, a research front develops when authors cite a paper to indicate its relevance to their own research. Papers that are frequently cited together, or cocited, share common features, such as topics, results, methods, or discussion. In this way, the citing authors themselves categorize papers into subject-related clusters of research. These cocitation groups then identify research fronts. >From the Framingham Heart Study, for example, six of Kannel's papers (see table on page 21) have been identified--along with 22 others from separate research groups--as seminal, or core, articles in the field of hypertension. According to SCI data, these core articles were cited in more than 370 journal articles published in 1989. These papers, along with the 28 core documents, make up ISI's 1989 research front on the relationship between systolic hypertension and coronary heart disease. With the addition of the Offspring Study, the Framingham Heart Study has more than doubled its initial intended follow-up of 20 years. As a result, says Kannel, "we now have some of the best data on the elderly population available." Under the medical directorship of NHLBI's William Castelli, who succeeded Kannel, researchers now are exploiting the data from the aging original cohort in order to learn more about diseases particular to the aging population. These diseases, in addition to coronary problems, include senile dementia, Alzheimer's disease, arthritis, cancer, and hearing and vision problems. Although the study is scheduled to end in a couple of years, the volumes of data collected over the past 42 years will continue to be valuable resources for future researchers. Framingham may be not be the largest city in the state of Massachusetts, but it is a thriving metropolis in the state of cardiology. Lisa Holland is a freelance science writer based in New Milford, Conn.

Getting To The Heart Of The 40-Year-Long Framingham Study

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