Review of clinical trials: proving the lipid hypothesis.

The Lipid Hypothesis, which states that lowering blood cholesterol levels should significantly reduce the incidence of coronary heart disease (CHD), has been repeatedly tested in primary and secondary intervention trials. Viewed as a whole, it is apparent that the incidence of CHD in treated groups decreased in proportion to the degree of plasma cholesterol reduction. An early study at the Wadsworth Hospital in Los Angeles showed that a diet high in polyunsaturated fat and low in cholesterol reduced the incidence of CHD. The Oslo study of diet and smoking intervention demonstrated a significant decrease in CHD concomitant with a 13% reduction in serum cholesterol achieved through a low saturated-fat diet and cessation of smoking. In the World Health Organization primary prevention trial, clofibrate reduced serum cholesterol by 9% and first clinical episodes of myocardial infarction by 20%. There was a 37% rise in total mortality, but no causal link with clofibrate has been found, and this was not significant when corrected for age at death. A secondary trial, the Coronary Drug Project, demonstrated that oestrogen and dextrothyroxine were clearly toxic. In this trial, niacin produced a 10% fall in serum cholesterol and mortality was 11% lower than in the placebo group after long-term follow-up. The Lipid Research Clinics-Coronary Primary Prevention Trial (LRC-CPPT) found an 8% reduction in plasma cholesterol and a 19% reduction in the incidence of CHD in the group treated with cholestyramine compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)