Seven Countries Study
Encyclopedia
The Seven Countries Study is an important epidemiological study. It is a large longitudinal study
. It 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.
, had postulated a correlation between increased cholesterol (hypercholesterolemia
) and coronary heart disease. To test his hypothesis, he completed a longitudinal study of businessmen in Minnesota, USA. This study was very special for its time, because it was a prospective study. The participants of this study were followed for 15 years. A. Keys was able to persuade many researchers to join him in a similar, but much larger, research project, the Seven Countries Study.
The Seven Countries Study was started in 1958. In total, 12763 men, 40-59 years of age, were enrolled. The study included 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 are in Finland, one in the Netherlands, three in Italy, five in the former country of Yugoslavia (today, two in Croatia, and three in Serbia), two in Greece, and two in Japan. The entry examinations into the study were performed between 1958 and 1964. The average participation rate was 90%. The lowest participation rate was in the USA, with 75%. The highest participation rate was in one of the Japanese cohorts, with 100%. The Seven Countries Study has been continued for more than 50 years.
The Seven Countries Study showed that increased cholesterol (hypercholesterolemia
) increases cardiovascular risk both at the population level and at the individual level. It demonstrated that the association between increased cholesterol and coronary heart disease (CHD) is homogeneous across different cultures. In addition, in the subgroup of participants who suffered from cancer, the study revealed that increased cholesterol and being overweight or obese increases mortality from cancer.
Objective data showing that Mediterranean diet
is healthy first originated from the Seven Countries Study. It was noted that coronary deaths in the United States and Northern Europe greatly exceed those in Southern Europe, even when controlled for age, cholesterol, blood pressure, smoking, physical activity, and weight. When investigated also by further research groups, the importance of Mediterranean diet was revealed. What exactly is meant by «Mediterranean diet» today, and its benefits, have been published, amongst others, by Walter Willett
, Harvard University
, including a book for the general public.
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 not so healthy, less active lifestyle and a diet slowly 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. These and other research findings made it possible to calculate the probability of 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. Surprisingly, 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 factor in the development of coronary heart disease, leading to 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 showed that cardiovascular risk factors in mid life are significantly associated with increased risk of dementia death later in life.
The study began with a great many more countries - Australia, Italy, Canada, Ceylon, Chile, Denmark, Finland, France, West Germany, Ireland, Israel, Japan, Mexico, Holland, New Zealand, Norway, Portugal, Sweden, Switzerland, Great Britain, USA - but Keys deleted the countries whose results did not match his pre-conceived conclusions, leaving him with only Japan, Italy, Great Britain, Australia, Canada and the US. Full disclosure would have made a great deal of difference.
One of the major conclusions of the study, that dietary saturated fat correlates with increased risk of heart disease, has come under serious fire, and rightly so.
:
http://www.sph.umn.edu/epi/history/sevencountries.asp
Longitudinal study
A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the...
. It was the first study to systematically examine the relationships between lifestyle, diet, coronary heart disease
Coronary heart disease
Coronary artery disease is the end result of the accumulation of atheromatous plaques within the walls of the coronary arteries that supply the myocardium with oxygen and nutrients. It is sometimes also called coronary heart disease...
and stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
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 of the Seven Countries Study
In the 1940s, a researcher, Ancel KeysAncel Keys
Ancel Benjamin Keys was an American scientist who studied the influence of diet on health. In particular, he hypothesized that different kinds of dietary fat had different effects on health....
, had postulated a correlation between increased cholesterol (hypercholesterolemia
Hypercholesterolemia
Hypercholesterolemia is the presence of high levels of cholesterol in the blood. It is not a disease but a metabolic derangement that can be caused by many diseases, notably cardiovascular disease...
) and coronary heart disease. To test his hypothesis, he completed a longitudinal study of businessmen in Minnesota, USA. This study was very special for its time, because it was a prospective study. The participants of this study were followed for 15 years. A. Keys was able to persuade many researchers to join him in a similar, but much larger, research project, the Seven Countries Study.
The Seven Countries Study was started in 1958. In total, 12763 men, 40-59 years of age, were enrolled. The study included 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 are in Finland, one in the Netherlands, three in Italy, five in the former country of Yugoslavia (today, two in Croatia, and three in Serbia), two in Greece, and two in Japan. The entry examinations into the study were performed between 1958 and 1964. The average participation rate was 90%. The lowest participation rate was in the USA, with 75%. The highest participation rate was in one of the Japanese cohorts, with 100%. The Seven Countries Study has been continued for more than 50 years.
Major findings
Many hundred medical papers have been published in relation to the Seven Countries Study. It is generally accepted by healthcare professionals that the study is very useful.The Seven Countries Study showed that increased cholesterol (hypercholesterolemia
Hypercholesterolemia
Hypercholesterolemia is the presence of high levels of cholesterol in the blood. It is not a disease but a metabolic derangement that can be caused by many diseases, notably cardiovascular disease...
) increases cardiovascular risk both at the population level and at the individual level. It demonstrated that the association between increased cholesterol and coronary heart disease (CHD) is homogeneous across different cultures. In addition, in the subgroup of participants who suffered from cancer, the study revealed that increased cholesterol and being overweight or obese increases mortality from cancer.
Objective data showing that Mediterranean diet
Mediterranean diet
The Mediterranean diet is a modern nutritional recommendation inspired by the traditional dietary patterns of southern Italy, Crete and much of the rest of Greece in the 1960s....
is healthy first originated from the Seven Countries Study. It was noted that coronary deaths in the United States and Northern Europe greatly exceed those in Southern Europe, even when controlled for age, cholesterol, blood pressure, smoking, physical activity, and weight. When investigated also by further research groups, the importance of Mediterranean diet was revealed. What exactly is meant by «Mediterranean diet» today, and its benefits, have been published, amongst others, by Walter Willett
Walter Willett
Walter Willett, MD, DrPH., is an American physician and nutrition researcher. Currently, Willett is the Fredrick John Stare Professor of Epidemiology and Nutrition, and Chair of the Department of Nutrition at Harvard School of Public Health...
, Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
, including a book for the general public.
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 not so healthy, less active lifestyle and a diet slowly influenced by the Western pattern diet
Western pattern diet
The Western pattern diet, also called Western dietary pattern or the meat-sweet diet, is a dietary habit chosen by many people in developed countries, and increasingly in developing countries. It is characterized by high intakes of red meat, sugary desserts, high-fat foods, and refined grains...
, 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
Framingham Heart Study
The Framingham Heart Study is a long-term, ongoing cardiovascular study on residents of the town of Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation of participants...
, Nurses' Health Study
Nurses' Health Study
The Nurses Health Study, established in 1976 by Dr. Frank Speizer, and the Nurses' Health Study II, established in 1989 by Dr. Walter Willett, are the most definitive long-term epidemiological studies conducted to date on older women's health. The study has followed 121,700 female registered...
, Women's Health Initiative
Women's Health Initiative
The Women's Health Initiative was initiated by the U.S. National Institutes of Health in 1991. The objective of this women's health research initiative was to conduct medical research into some of the major health problems of older women...
, confirmed not only the importance of healthy diet, but also of not being overweight
Overweight
Overweight is generally defined as having more body fat than is optimally healthy. Being overweight is a common condition, especially where food supplies are plentiful and lifestyles are sedentary...
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. These and other research findings made it possible to calculate the probability of developing coronary heart disease in the future.
The Seven Countries Study demonstrated that elevated blood pressure (hypertension
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
) increases risk of coronary heart disease and stroke. It showed that the mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
after a coronary heart disease event or stroke can be influenced by the level of hypertension. Surprisingly, 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
Smoking
Smoking is a practice in which a substance, most commonly tobacco or cannabis, is burned and the smoke is tasted or inhaled. This is primarily practised as a route of administration for recreational drug use, as combustion releases the active substances in drugs such as nicotine and makes them...
is a highly significant factor in the development of coronary heart disease, leading to angina pectoris, myocardial infarction
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
(MI), and coronary death, along with other important studies about smoking, e.g. the Framingham Heart Study
Framingham Heart Study
The Framingham Heart Study is a long-term, ongoing cardiovascular study on residents of the town of Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation of participants...
and the British Doctors Study
British Doctors Study
The British Doctors Study is the generally accepted name of a prospective cohort study which ran from 1951 to 2001, and in 1956 provided convincing statistical proof that tobacco smoking increased the risk of lung cancer.-Context:...
.
The Seven Countries Study revealed the importance of good cardiovascular health in avoiding dementia in the general population. It showed that cardiovascular risk factors in mid life are significantly associated with increased risk of dementia death later in life.
Criticism
The Seven Countries Study had weak points, including how the populations were selected (in part for reasons of convenience), and how the population correlations were carried out; there was no random selection of a great numbers of units. Also, this study included only men. Hence, generalisability of the findings to women should be done with caution.The study began with a great many more countries - Australia, Italy, Canada, Ceylon, Chile, Denmark, Finland, France, West Germany, Ireland, Israel, Japan, Mexico, Holland, New Zealand, Norway, Portugal, Sweden, Switzerland, Great Britain, USA - but Keys deleted the countries whose results did not match his pre-conceived conclusions, leaving him with only Japan, Italy, Great Britain, Australia, Canada and the US. Full disclosure would have made a great deal of difference.
One of the major conclusions of the study, that dietary saturated fat correlates with increased risk of heart disease, has come under serious fire, and rightly so.
Personal historical account
A personal historical account by one of the researchers of the Seven Countries Study can be found on a webpage of the University of MinnesotaUniversity of Minnesota
The University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States. It is the oldest and largest part of the University of Minnesota system and has the fourth-largest main campus student body in the United States, with 52,557...
:
http://www.sph.umn.edu/epi/history/sevencountries.asp