Coronary artery disease: the role of lipids, hypertension and smoking

Abstract

Pioneering epidemiological projects such as the Seven Countries study, and the Framingham Heart study established the classical risk factor concept for coronary heart disease (CAD). These landmark studies showed that a raised serum total cholesterol, high blood pressure (systolic and diastolic) and smoking increase the risk of developing CHD in men and women in a graded fashion. Women develop CHD about 10 years later than men and women's risk is smaller. In the years and decades following these early studies many more prospective cohort studies primarily in the US and Europe have confirmed the early findings. In Germany two occupational and one population based cohort studies have contributed further information on this topic. In addition interactions between the three classical risk factors have been quantified, demonstrating for example that smoking carries a much higher risk for CHD in persons with high cholesterol values.

Most cohort studies have confirmed that the relative risks for the classical risk factors are very similar. However, the respective absolute risks can differ tremendously, indicating that many more factors such as socio-economic conditions, nutrition, physical activity and others are of importance for the development of CHD.

The scientific community, however, did not accept the consistent findings from the many observational studies as proof of causality. They required evidence that the risk for CHD could be reduced when the respective risk factor(s) was (were) diminished or eliminated.

The late 1960s early 1970s thus saw the beginning of the era of randomized controlled trials (RCTs) following the advice of Archibald Cochrane who once wrote “we have to find that point on the distribution curve where therapy does more good than harm”.

We now know from meta-analyses of RCTs that a 1% reduction in serum cholesterol produces a 2–3% decline in risk for CHD and we can achieve reductions in total cholesterol of 20% or more. Regarding treatment of high blood pressure, meta-analyses of RCTs have shown that a reduction of 1 mmHg in diastolic blood pressure (DBP) produces a 2–3% decline in risk of CHD, and we can achieve reductions in DBP on average of 5–6 mmHg. With regard to smoking cessation, observational studies have shown that within 1–5 years of cessation those who stop smoking have a 50–70% lower risk than current smokers.

Thus the findings from observational studies, RCTs and studies on mechanisms have clearly established the importance of the three classical risk factors for CHD. The successful treatment of these risk factors will not only lower the burden of CHD in the population but promises to be the most effective way of improving the health of the whole population.