Seven Countries Study

The Seven Countries Study is an epidemiological longitudinal study that was the first study to systematically examine the relationships between lifestyle, diet, coronary heart disease and stroke in different populations from different regions of the world. It directed attention to the causes of coronary heart disease and stroke, but also showed that an individual’s risk can be changed.

History
In the 1940s, a University of Minnesota researcher, Ancel Keys, postulated that the apparent epidemic of heart attacks in middle-aged American men was related to their mode of life and possibly modifiable physical characteristics. He first explored this idea in a group of Minnesota business and professional men that he recruited into a prospective study in 1947, the first of many cohort studies eventually mounted internationally. The men were followed through 1981 and the first major report appeared in 1963 after the fifteen-year follow-up study. The study contributed much to survey methods and confirmed the results of larger studies that reported earlier on the predictive value for heart attack of several characteristics measured in health, the now-traditional risk factors of blood pressure and blood cholesterol level and cigarette smoking. Meanwhile, in the mid-1950s, with improved methods and design, Keys recruited collaborating researchers in seven countries to mount the first cross-cultural comparison of heart attack risk in populations of men engaged in traditional occupations in cultures contrasting in diet, especially in the proportion of fat calories of different composition, the Seven Countries Study still under observation today.

The Seven Countries Study was formally started in fall 1958 in Yugoslavia. In total, 12,763 men, 40–59 years of age, were enrolled as 16 cohorts, in seven countries, in four regions of the world (United States, Northern Europe, Southern Europe, Japan). One cohort is in the United States, two cohorts in Finland, one in the Netherlands, three in Italy, five in Yugoslavia (two in Croatia, and three in Serbia), two in Greece, and two in Japan. The entry examinations were performed between 1958 and 1964 with an average participation rate of 90%, lowest in the USA, with 75% and highest in one of the Japanese cohorts, with 100%. The Seven Countries Study has continued for more than 50 years. The above reference summarizes its principal findings.

Major findings
The Seven Countries Study showed that the risk and rates of heart attack and stroke cardiovascular risk both at the population level and at the individual level was directly and independently related to the level of total serum cholesterol. It demonstrated that the association between blood cholesterol level and coronary heart disease (CHD) risk from 5 to 40 years follow-up is found consistently across different cultures. Cholesterol and overweight or obesity was associated with increased mortality from cancer.

Objective data on CVD health in relation to the Mediterranean diet originated from the Seven Countries Study. Coronary deaths in the United States and Northern Europe greatly exceeded those in Southern Europe, even when controlled for age, cholesterol and blood pressure levels, smoking, physical activity, and weight. When investigated further, the importance of the eating pattern characterized as the Mediterranean diet became clear. What exactly is meant by "Mediterranean diet" today, and its benefits, is detailed by other researches: Walter Willett of Harvard University,

The Seven Countries Study also showed that the slowly changing habits of a population in the Mediterranean region, from a healthy, active lifestyle and diet, to a less active lifestyle and a diet influenced by the Western pattern diet, significantly increases risk of heart disease. Meanwhile, it has been confirmed by other researchers that there is an inverse association between adherence to the Mediterranean diet and the incidence of fatal and non- fatal heart disease in initially healthy middle-aged adults in the Mediterranean region.

The Seven Countries Study, along with other important large studies, e.g. the Framingham Heart Study, Nurses' Health Study, Women's Health Initiative, confirmed not only the importance of healthy diet, but also of not being overweight or obese, and of regular exercise, in maintaining good general health. It also showed that regular exercise and dietary fibre strongly influence body fat levels [citation needed]. These and other research findings made it possible to calculate the probability of an individual developing coronary heart disease in the future.

The Seven Countries Study demonstrated that elevated blood pressure (hypertension) increases risk of coronary heart disease and stroke. It showed that the mortality rate after a coronary heart disease event or stroke can be influenced by the level of hypertension. In several cohorts of the study, stroke deaths exceeded deaths from coronary heart disease.

The Seven Countries Study showed that differences in overall mortality between the different regions of the world are largely accounted for by the variation in cardiovascular mortality.

The Seven Countries Study confirmed that cigarette smoking is a highly significant predictor of the development of coronary heart disease, leading to excess rates of angina pectoris, myocardial infarction (MI), and coronary death, along with other important studies about smoking, e.g. the Framingham Heart Study and the British Doctors Study.

The Seven Countries Study revealed the importance of good cardiovascular health in avoiding dementia in the general population. It also showed that cardiovascular risk factors in mid life are significantly associated with increased risk of dementia death later in life.

Criticism
Critics of the Seven Countries Study (like Gary Taubes) say, "Keys chose seven countries he knew in advance would support his hypothesis." If Gary Taubes is correct, then Ancel Keys provides researchers with little to no valuable clinical information.