10.2.2. Plasma cholesterol levels.

Observational studies performed in the 60’s showed that the average level of total plasma cholesterol in different countries is associated with the country specific mortality for Coronary Heart Disease (CHD). Subsequently, the existence of a continuous and graded association between plasma cholesterol levels and CHD risk was convincingly proven by a number of epidemiological studies. The association extends to values of plasma cholesterol well below those usually observed in developed countries (now around 200 mg/dL). A 10% increase in plasma total cholesterol is associated with an increase of 27% in CHD incidence, which is a good indicator of the magnitude of the public health problem associated with hyperlipidemia. On the other hand, a 10% reduction in plasma total cholesterol is followed by a 25% reduction in CHD incidence after 5 years. CHD is rare in populations with total cholesterol less than 3-4 mmol/l (~ 115-155 mg/dl).

Various studies have recognised that any reduction of plasma LDL cholesterol levels by 1% will induce, in a 5 years time, a 1% reduction of CVD incidence. The ischemic stroke risk was also diminished in many of these trials, even if the association of stroke with plasma cholesterol levels is weak, or absent, in most epidemiological studies. From a mechanistic point of view, cholesterol reduction has been shown to slow atheroma progression, and/or to induce regression, to improve endothelial function and vasomotion, to modulate the inflammatory responses involved in the atherosclerotic process and to stabilize the atherosclerotic lesions.

Desirable goal for people who tend to stay healthy is below 5 mmol/l (~ 190 mg/dl). High Density Lipoprotein (HDL) fraction has a protective effect on CVD. HDL less than 1.2 mmol/l (~ 40-45 mg/dl) is considered a marker of increased risk that should suggest greater attention to lifestyle. Nowadays, an improved knowledge of the importance of physical activity and dietary interventions useful to control plasma cholesterol levels as well as the availability of drugs able to inhibit cholesterol synthesis and absorption makes it possible to reach the proper therapeutic target (plasma cholesterol levels ranging from 70 mg/dL in very high risk patients to 160 mg/dL in very low risk subjects) in the large majority of individuals considered for CVD prevention.

For more details and references, see Chapter 5.2.