CAUSES OF ACQUIRED HEART DISEASE
The US government decided in 1948 to investigate the causes of heart disease by looking at what was deemed to be a typical small town in the USA: Framingham, a hardworking, decent community of people, mostly white and middle-class and, what was particularly useful for the investigators, very stable. Framingham folk do not, or rather did not, move about the country a lot. Thirty years after the study was started the researchers were still able to keep tabs on 80 percent of the population, which by any reckoning is quite extraordinary.
The Framingham study drew on the services of just over 5000 people - 2282 men and 2845 women (from a total population of 28000). All were healthy volunteers; all were prepared to take part in an experiment that might well last as long as they did. Physical checks and tests were carried out on all of them: blood tests, ECGs to measure heart function, X-rays and blood-pressure readings and so on and detailed medical histories on previous illnesses that they or their families had had were compiled. Once this huge initial data-gathering phase was completed, the researchers saw the 5000 every two years for re-examination, and kept in touch with the subjects' physicians on any health problems that arose. Otherwise they just sat back and waited.
Five factors associated with CHD
Over 10, 20, 30 years the participants began to die, and where possible postmortems were conducted to ascertain the causes of death in detail. The research revealed five important factors associated with death caused by CHD:
- High blood pressure.
- High levels of cholesterol in the blood.
- Glucose intolerance, such as is found in diabetics.
- Evidence of hypertrophy (abnormal enlargement) of the left ventricle.
When these findings were first aired publicly they caused something of a sensation. Americans had at best only a vague idea of what cholesterol was, but they saw that it was doing them no good. They saw, too, that a generally fitter style of living - more exercise and fresh air, and less food, cigarettes and booze - might lessen their chances of a heart attack.
Subsequently many more studies have been carried out along similar lines to the Framingham investigation. In 1976 alone, for example, the American National Heart Institute and the American Heart Association invested a cool 400 million dollars on research into the causes of heart disease. A lot of money, until you realize that, measured in terms of hospital care, insurance claims, loss of manpower and so on, the costs of heart disease in the USA during that period totalled a staggering 58 billion dollars.
Since then the list of risk factors has been enlarged and refined. At the top come cigarette-smoking, hypertension (high blood pressure), and high blood cholesterol, which operate independently of any other factors. If you can admit to any of these you are at risk. Then comes a secondary list of factors that tend to operate in conjunction with others, sometimes several 'or more at a time. These include diabetes and a family history of CHD. There are also those factors that might increase your risk: being overweight; suffering stress; having a particular personality; being physically inactive; living in an area with hard drinking-water.
Weighing up your chances
As we have seen from the Framingham and other studies, if you are a cigarette smoker and have high levels of cholesterol in your blood and high blood-pressure, there is little doubt that you are more prone to CHD. Imagine, however - and this is very interesting to me as someone who has seen all kinds of patients over the years - that you do have all these factors; even so, your chances of contracting CHD in the next ten years are only one in five. Although you are in the maximum-risk category you still have an 80 percent chance of avoiding a coronary.
CARDIO & BLOOD
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