THE SEVEN COUNTRIES STUDY: THE LESSONS FOR CARDIOVASCULAR SPECIALISTS

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1 194 THE SEVEN COUNTRIES STUDY: THE LESSONS FOR CARDIOVASCULAR SPECIALISTS ALESSANDRO MENOTTI, MD, PhD, for the SEVEN COUNTRIES STUDY RESEARCH GROUP The Seven Countries Study (SCS) is a classical epidemiological observational study that began in the 1950s and was carried out for 25 years. The study had 16 population samples of men, aged 40 to 59 y at entry, who live in seven different countries in three continents (United States, Japan, Finland, The Netherlands, Italy, former Yugoslavia, and Greece). At entry field examination, several individual characteristics of biophysical, biochemical, behavioral, clinical, and nutritional variables were measured. Similar examinations were repeated after 5 and 10 years. Incidence of cardiovascular diseases was measured for the first 10 years of follow-up and vital status and causes of death for 25 years. The SCS was the first study to demonstrate the existence of true differences in prevalence, incidence, and mortality from coronary heart disease (CHD) among different and contrasting populations, with higher rates in North America and northern Europe and lower rates in southern Europe and Japan. A large proportion of these differences could be attributed to population differences in nutrient intake and risk factors. High, positive, and significant correlations and regression coefficients were found in CHD at mean levels, mainly in saturated fatty-acid consumption and serum cholesterol and partly in blood pressure. Moreover, the relationship of risk factors to individual risk ofchd was found within each country. These findings became the empirical and theoretical bases for the population strategy of primary prevention of CHD, having shown the mass origin of mass morbid phenomenon. AFTER THE Second World War, in the 1950s, several investigators discussed their interest of studying a new epidemic which began to affect industrialized countries. The decline in morbidity and mortality from infectious diseases and malnutrition was largely substituted by increasing trends in morbidity and mortality from cardiovascular diseases, particularly coronary heart disease (CHD). However, there were substantial uncertainties about the real dimension of the phenomenon, the existence of real differences in morbidity and mortality from CHD among populations, and the possible causes of the disease and its widespread diffusion. During this time, the era of cardiovascular epidemiology began and some From the Division of Epidemiology, University of Minnesota, Minneapolis, Minnesota, USA, and Cardioricerca, Rome, Italy. Address reprint requests and correspondence to Dr. Menotti: Cardioricerca, Via Adda 87, Rome 00198, Italy. historically classic studies were carried out. Among them, the Seven Countries Study of Cardiovascular Diseases was the first study to pose questions and to seek for answers at the intemationallevel. A group of scientists with different backgrounds, led by Professor Ancel Keys, from the University of Minnesota, promoted this study after years of exploratory and pilot studies and after developing a standardized methodology that had been strictly tested. The Seven Countries Study (SCS) tried to answer the following questions: (1) whether different and contrasting populations suffered real differences in cardiovascular diseases, in general, and CHD, in particular; (2) whether these differences, if any, could be partly explained by lifestyles, eating habits, and other general characteristics of the populations themselves; and (3) whether, within each population, individual characteristics (later named risk factors) were able to predict the occurrence of CHD morbid and fatal events.

2 SEVEN COUNTRIES STUDY Materials and Methods The entry examination of the SCS was held between 1958 and 1964 on 12,763 men, aged 40 to 59 y, in 16 cohorts in seven counties.i.2 Eleven cohorts comprised more than 95% of all men in that age range in geographically-defined rural areas in Finland (2 cohorts), Italy (2 cohorts), former Yugoslavia ( 3 cohorts), Greece (2 cohorts), and Japan (2 cohorts). A statistically-defmed four-ninths sample of all men, aged 40 to 59 y, was enrolled in Zutphen, a small commercial town in The Netherlands. A cohort was provided by a large agroindustrial cooperative in Zrenjanin, Serbia (Yugoslavia) and another was made up of faculty of the University of Belgrade (Yugoslavia). Finally, two cohorts of railroad employees in specific occupations were enrolled, one trom the midwest and northwest of the United States and the second from the Rome Division of the Italian State Railroad. Overall, participation rate was more than 90%, with several cohorts reaching close to 100%.J A number of measurements were taken at entry and subsequent examinations, including information on lifestyle obtained by questionnaire, the measurement of biophysical and biochemical variables, a clinical questionnaire and physical examination, recording of blood pressure, resting and post-exercise electrocardiograms, and data on dietary habits; the information was collected by different methods. 1-5 Similar examinations were repeated after 5 and 10 years, and in some cohorts also after 15,20, and 25 years. Incidence of major cardiovascular diseases was estim'ltf"n for the first 1 0 years in all cohorts. Data on vital status, mortality, and causes of death were collected in all cohorts for 25 years with minimal losses to follow-up (56 subjects, more than 12,000). Details on methods, procedures, and criteria can be found elsewhere.i-j In general, methods and procedures for most measurements were highly standardized, under strict quality control and, when possible, centralized (such as cholesterol measurement, chemical analysis of food composites, ECG readings and coding, final allocation of clinical diagnoses, and causes of death). Analyses for the report followed two different approaches: (1) the ecological approach, when the statistical units were made of single cohorts or pools of national cohorts (inter-cohort comparisons); in this context, for some purposes, former Yugoslavia was split into two components, i.e., Croatia and Serbia, due to their background differences as different nations; and (2) the individual approach, when the statistical units were made of individuals within single cohorts or nations, or within larger pools (inter-individual comparisons). Both univariate analyses and different multivariate models were considered. Differences Among Cohorts in Risk Factor Levels, Incidence, and Mortality from CUD Identification of cohorts, number of men examined, and participation rates are given in Table 1. At entry examination, large differences were found in mean levels of some cardiovascular risk factors and personal characteristics among cohorts. In particular, serum cholesterol was the highest in Finland, United States, and The Netherlands (> 6 mmolll), lower in southern Europe ( ::; 5.4 mmol/l), and with lowest levels in Serbia (former Yugoslavia) and Japan.I.2 Blood pressure was also higher in northern European cohorts than in other groups but differences were smaller. 1,2 The highest prevalence of smokers was found in The Netherlands and in Japan.I.2 The most contrasting eating habit was the intake of saturated fatty acids, ranging between 20% and above (as proportion of total energy intake) in Finland, The Netherlands and United States; in southern Europe and Japan2.4.5the percentages were 10% and 3%, respectively. CHD incidence and mortality, for variable periods of follow-up. This approach usually considered the use of regression equations and correlations, with mean population levels of risk factors as independent variables and CHD incidence or mortality rates as dependent variables. During follow-up, CHD incidence (for the first 10 years) and CHD mortality (for several variable periods offollow-up, up to 25 years) strongly and significantly correlated to population levels of serum cholesterol, systolic and diastolic blood pressure among risk factors, and saturated fat consumption, the ratio of polyunsaturated to saturated fatty-acid (PIS ratio) consumption (inverse), the ratio of monounsaturated to saturated fatty-acids (MIS ratio) (inverse), and carbohydrates among major nutrients. Poor relationships were found with body mass index, smoking habits, and skinfold thickness. Highly significant correlations were also found between population intake of saturated fatty acids and population mean levels of serum cholesterol This means that, at least ITom the observational point of view, high levels of serum cholesterol and blood.

3 196 MENOTII The early results ofthe study, related to the first 5 years of follow-up, showed for the first time the existence of large and true differences in prevalence, incidence, and mortality from CHD among different nations and different cohorts in different countries, studied by the same standardized protocoj.2 Those early data showed the highest levels ofchd incidence and mortality in northern European (particularly in Finland) and north American samples, lower or definitely low levels in southern European and Mediterranean cohorts, and very low levels in Japan (Table 2). Overall, the difference in 5-year incidence was about lo-fold comparing Finland with Japan and about IS-fold comparing the cohort with the highest level (East Finland) with that having the lowest level (Crete). These differences roughly reflected those suggested by the official mortality data that have been collected, collated, and distributed by the World Health Organization. Findings by the SCS, however, were based on a standardized and comparable methodology. Similar experience was found for CHD incidence after Table 2. Five-year incidence per 10,000 ofchd events in CHDfree men at entry examination in seven countries. * Country CHD Myocardial Angina Other All death infarction pectoris CHD CHD Finland United States Netherlands Italy Yugoslavia Greece Japan *From the Seven Countries of Cardiovascular Diseases. CHD = coronary heart disease. Table 3. Rank position of cumulative quinquennial death rates from typical CHD (sudden death andfatal myocardial infarction) during 25 years offollow-up. * Country 5 Years 10 Years 15 Years 20 Years 25 Years Finland United States Netherlands Italy Croatia Serbia Greece Japan *From the Seven Countries Study of Cardiovascular Diseases. CHD = coronary heart disease. 10 years of follow-up.3 Comparisons of cumulative death rates from CHD at quinquennial intervals (from year 5 up to year 25) confirmed the wide range of CHD mortality among cohorts and nations.6.7 However, changes in the rank order of death rates were recorded among nations after a 10-year followup, with the Serbian cohorts overtaking all the other southern European groups, from low levels to cumulative rates that are similar to those of northern Europe (Table 3). Explanation of Inter-cohort Differences in the Burden of CHD A number of "ecological" analyses were conducted to relate entry population levels of risk factors and other personal characteristics to CHD incidence and mortality, for variable periods of follow-up. This approach usually considered the use of regression equations and correlations, with mean population levels of risk factors as independent variables and CHD incidence or mortality rates as dependent variables. During follow-up, CHD incidence (for the first 10 years) and CHD mortality (for several variable periods offollow-up, up to 25 years) strongly and significantly correlated to population levels of serum cholesterol, systolic and diastolic blood pressure among risk factors, and saturated fat consumption, the ratio of polyunsaturated to saturated fatty-acid (PIS ratio) consumption (inverse), the ratio of monounsaturated to saturated fatty-acids (MIS ratio) (inverse), and carbohydrates among major nutrients. Poor relationships were found with body mass index, smoking habits, and skinfold thickness. Highly significant correlations were also found between population intake of saturated fatty acids and population mean levels of serum cholesterol This means that, at least ITom the observational point of view, high levels of serum cholesterol and blood pressure and a rich diet (rich in fat and saturated fatty acids and poor in poly- and monounsaturated fatty acids) are associated with higher incidence and mortality from CHD and vice versa. Examples of these correlations are given in Tables 4 and 5. After 25 years of follow-up, the relationship of population mean levels of serum cholesterol to CHD mortality, although still positive and significant, was definitely weaker than for shorter follow-up periods6 due to changes in the rank order of CHD death rates, particularly for southern European cohorts such as the ones in Serbia. Journal of the Saudi Heart Association, \obi. 9, No.3, 1997

4 SEVEN COUNTRIES STUDY 197 Table 4. Correlation coefficients between population mean levels 0/ some risk/actors and CHD events. * Population CHD Follow-up Correlation Lower CI risk factor end-point duration (y) coefficient Cholesterol Incidence Cholesterol Death Cholesterol Death Systolic BP Death Systolic BP Death Cigarettes Death Cigarettes Death Body mass index Death Body mass index Death Physical activity Death Physical activity Death Multiple regressiont Death Multiple regressiont Death *From the Seven Countries Study of Cardiovascular Diseases twith cholesterol, systolic blood pressure, cigarettes, body mass index, and physical activity as predictors. CHD = coronary heart disease; CI = confidence interval; BP = blood pressure. Upper CI Table 5. Correlation coefficients between population mean levels 0/ some nutrient intake and CHD event rates in 16 cohorts. * Population CHD Follow-up Correlation Lower CI Upper CI nutrient end-point duration (y) coefficient Total fat Incidence Total fat Death Saturated fats Incidence Saturated fats Death Monounsaturated fats Incidence PIS ratio Death MIS ratio Death Omega-3 fatty acids Death Proteins Incidence 5 O Carbohydrates Death *From the Seven Countries of Cardiovascular Diseases. CHD = coronary heart disease; CI = confidence interval. Prediction of CHD Events by Multivariate Approach Incidence and mortality trom CHD for different follow-up periods, for single cohorts, pools of national cohorts, and pools of nations were used as end-points in multivariate estimates of predictivity as a function of individual characteristics known as cardiovascular risk factors. Pooling of cohorts was needed when, during short follow-up periods, incident or fatal events were too few in single cohorts. The most commonly used models were the multiple logistic function and the proportional hazards model. Examples are given in Table 6. Basically, age, serum cholesterol, systolic (and diastolic) blood pressure, smoking habits and, to a lesser extent, body mass index and sedentation were directly related to the occurrence of new CHD events or to CHD deaths, with "weights" determined by the estimated coefficients of the multivariate models '2-'4 The back application of coefficients and constant of the equation to single individuals of the same population which produced the model allowed to estimate and to rank the individual probabilities of a CHD event in a given period of time. These probabilities increased in subgroups with low estimated risk to groups with high estimated risk, with large correlation coefficients between estimated and observed CHD cases in these subgroups. The risk ratio between extreme classes was in the range of 5 to 10 and above, depending upon the model.

5 198 MENOITI Table 6. Solutions of the multiple logistic function with six riskfactors predicting coronary deaths in 10 years in three regions. * Region Const. Age SBP CHOL CIG PULSE PHY ACT USA coeff SE T-value O.ll * From the Seven Countries Study of Cardiovascular Diseases. USA = United States of America; NEU = northern Europe; SEU = southern Europe; SBP = systolic blood pressure; CHOL = serum cholesterol; CIG = cigarettes consumption; PULSE = pulse rate; PHY ACT = physical activity. Table 7. Prediction ofchd deaths in one regionfrom the logistic coefficients of another region. Model with 5 riskfactors predicting events in J 5 years. * Solutions Predicting CHD Ratio expected/ deaths in observed SEU NEU 0.53 SEU USA 0.76 SEU Japan 2.17 NEU SEU 1.89 NEU USA 0.99 NEU Japan 4.54 USA SEU 1.92 USA NEU 1.04 USA Japan 4.54 Japan SEU 0.20 Japan NEU 0.06 Japan USA 0.09 *From the Seven Countries Study of Cardiovascular Diseases. CHD = coronary heart disease; SEU = southern Europe; NEU = northern Europe. Although bound only to these observational data, these findings suggested the likelihood of a multifactorial predictivity (if not causality) ofchdy, However, when the same back application was made, applying the coefficients of one population to the risk factor levels of another, the ranking of the risk (relative risk) was equally good3.7.9 but the estimate of absolute risk (Le., the actual number of cases) could be over- or underestimated as shown in Table 7. For example, the risk function of northern European cohorts overestimated incidence in southern Europe (and vice versa, the risk function of southern Europe underestimated incidence in northern Europe). On the other hand, risk functions of CHD from northern European cohorts predicted in an accurate way the incidence in North America and vice versa, suggesting that background ethnic factors or other factors, not measured in this study, were responsible for the proportion in differential incidence and mortality from Table 8. Relative risk ofchd mortality riskfor a difference of about J mmol/l (40 mg/dl) in serum cholesterol and 20 mm Hg in systolic blood pressure. estimated in 8 nations by proportional hazards multivariate models. * Nation Cholesterol Systolic BP RR Lower CI Upper CI RR Upper CI Lower CI USA Finland Netherlands Italy Croatia Serbia Greece Japan *From the Seven Countries Study on Cardiovascular Diseases CHD = coronary heart disease; BP = blood pressure; RR = relative risk; CI = confidence interval.

6 SEVEN COUNTRIES STUDY 199 CHD that were not explained by the available factors. In extensive analyses made on the 25-year mortality data,14 it was shown that for some major risk factors, the relative risk of CHD death for defmed differences in risk factor levels are largely similar in different populations and cultures (Table 8). This means that the biological and statistical relation of risk factors, such as serum cholesterol and blood pressure, to the disease is basically the same in different cultures and that differences in incidence and mortality are mainly due to different mean levels in risk factors, and, of course, to other unknown or nonmeasured factors. 14 Secular Trends in Population Risk Factor Levels and CUD Mortality During follow-up and repeated examinations, population mean levels of risk factors changed. A part of the change was related to the contemporary aging of population samples whose follow-up began at the same age range and with similar distributions. The change was very different among populations, suggesting that different secular trends are related to local circumstances. Trends in smoking habits were linked to a natural and expected decline with aging. Trends in blood pressure and serum cholesterol levels were different among different cohorts.3.6a summary of to-year changes is given in Table 9. In general, population serum cholesterol levels were relatively stable or declined in the United States, Finland, The Netherlands, and Japan, while there were increases in southern Europe, mainly in Serbian cohorts. At the same time, CHD death rates showed different trends among populations, with extraordinary relative increases in southern Europe and mainly in Serbian cohorts.6 For explanation of these differences, ecological analyses that included entry levels of population serum cholesterol, their changes in the first 10 years of follow-up, and the possible association with CHD rates in the next 15 years6 were studied. A multiple linear regression equation describing this approach (Table 10) suggests that CHD death rates between years 10 and 25 of follow-up are both predicted by entry levels of serum cholesterol (year 0) and by their I O-year changes, confmning the possibility that mass population changes (mainly increases) of serum cholesterol are followed by higher levels ofchd death rates. This corresponds to a type of observational natural experiment, bound to an inverse direction, compared with primary prevention trials. Table 9. Mean changes (percent) in serum cholesterol and systolic blood pressure levels during the first 10 years of follow-up in 16 cohorts. * Cohort US Railroad, USA CHOL SBP (5 years) (5 years) East Finland, Finland West Finland, Finland Zutphen, Netherlands Crevalcore, Italy + II Montegiorgio, Italy Rome Railroad, Italy Dalmatia, Croatia Siavonia, Croatia Velika Krsna, Serbia Zrenjanin, Serbia Belgrade, Serbia Crete, Greece Corfu, Greece Tanushimaru, Japan Ushibuka, Japan *From the Seven Countries Study of Cardiovascular Diseases. CHOL = serum cholesterol; SBP = systolic blood pressure. Table 10. Multiple linear regression ofchd death rates on 5 risk factors at entry and difference of cholesterol at year 10 minus cholesterol at year a (D-cholesterol-l 0) in the studied cohorts. The first 10 years offollow-up are excluded. * Risk factors t-values for follow-up of 10-15years years Cholesterol D-cholesterol-IO Body mass index Cigarettes Physical activity Systolic BP R R squared *From the Seven Countries of Cardiovascular Diseases. CHD = coronary heart disease; BP = blood pressure. Individual Changes in Risk Factors and Prediction of Cardiovascular Diseases During follow-up, changes in risk factor levels affected single individuals within cohorts, nations, and countries in different ways. The role of risk factor changes could therefore be also studied at individual levels and within cohorts, beyond the ecological change levels as described above. However, blood pressure was the only risk factor studied for individual changes,

7 200 MENOTII while only preliminary analyses were attempted for serum cholesterol and other factors. Changes in blood pressure during the first 10 years of follow-up (based on three measurements, corresponding to years 0,5, and 10) were estimated by different indicators such as the difference between levels at year 10 and year 0 or the risk-factor time integral, called delta. IS These changes have been used in a dycotomic way (subjects with relatively increasing V s are those with relatively decreasing levels identified by the median change) or as continuous variables"s The first approach is exemplified by Table II, where the relative risk of cardiovascular disease death between years I 0 and 20 of follow-up is reported (relative increase Vs and relative increase of blood pressure) in quartile classes of entry (year 0) blood pressure. In almost all cells, the relative risk is greater than one saying that, baseline blood pressure being similar, those exhibiting an increase of blood pressure are at higher risk for cardiovascular death than those exhibiting a decrease. This was true in different quartiles and in different cultures, as suggested by Table II where six national groups are compared. Similar conclusions were reached with a multivariate approach where blood pressure and its changes were fed as continuous variables. These findings somehow anticipated or confirmed results of drug trials of hypertension, but were bound to "spontaneous" change in blood pressure in individuals belonging to whole population groups and not to drug intervention in hypertensives only. In fact, changes in blood pressure were recorded in the I960s when treatment of high blood pressure was extremely rare and ineffective in these populations. These findings, too, represent a type of natural experiment observed among these different populations, although the precise causes of blood pressure changes are unknown. Conclusions Many other additional findings were found from the analyses of this study, at both intemationap6-39 and national levels. Although the study ended after 25 years of follow-up, it is still continuing with another name and organization in five areas of three countries (FINE Study: Finland, Italy, Netherlands Elderly), emphasizing health problems in the elderly and with a follow-up of35 years. The SCS is a classic study which has achieved some milestones in the knowledge of CHD epidemiology, causality, and prevention. The main lessons for clinicians and public health professionals can be summarized as follows: (1) different and contrasting populations may suffer largely different amounts of CHD; (2) large proportions of these differences, and perhaps causality, can be explained by different major lifestyles and characteristics of the populations, mainly in eating habits and population levels of serum cholesterol and partly in blood pressure; (3) within populations, the prediction of CHD events can be satisfactorily achieved by combining several risk factors in multivariate models; (4) population secular changes in serum cholesterol are followed by directly related changes in CHD mortality rates; and (5) individual changes in blood pressure are followed by different outcomes in cardiovascular disease mortality, with higher risk for those whose blood pressures relatively increase in years. These fmdings suggest that mass diseases, such as CHD, are largely due to mass phenomena and lifestyles, which could represent large portions in the causality of this condition. These facts represent the basis for the so-called population strategy of primary prevention, which points to substantial mass changes in lifestyle and distribution of major risk factors. Table II. Relative risk of CVD death for increase Vs decrease of SSP (expressed by an indicator of change) in age specific quartile classes of entry ssp. Changes of SSP in 10 years are related to mortality from CVD during the next 10 years.. Finland Netherlands Italy Yugoslavia Greece Japan Quartile I Quartile Quartile Quartile Surnrnaryt Frorn the Seven Countries Study of Cardiovascular Diseases. tmantel-haenszel technique. CVD = cardiovascular disease; SSP = systolic blood pressure.

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