Significance of high-density lipoprotein cholesterol.

The central importance of elevated blood cholesterol levels in the process of atherosclerotic heart disease (ASHD) is firmly established. Cholesterol is transported in the blood in conjunction with protein as a lipoprotein complex. The low-density lipoproteins (LDL) carry the bulk of the blood cholesterol. The high-density lipoproteins (HDL) occur in much smaller amounts. Recently it has been demonstrated that not only is the cholesterol carried in the HDL fraction not harmful, but appears to be protective against the development of ASHD. Data from Framingham and elsewhere seem consistent with this observation. The HDS apparently represent the fraction concerned with the efflux of cholesterol from the tissues, so that higher levels may represent a heightened cholesterol-riddance mechanism. Thus far, two circumstances seem to be associated with elevated levels of HDL--physical exercise and ethanol ingestion. The importance of these observations in the clinical management of the patient at risk is discussed.