ABSTRACT
Simplification of the complex topic dealt with in this chapter is essential if it is to be read by non-specialists – but oversimplification carries its own risks. For example, the term ‘cholesterol’ includes both free (unesterified) cholesterol and cholesterol ester, which differ markedly in their physical properties, tissue distribution and physiological functions. Thus, two-thirds of the cholesterol in plasma is normally esterified by the enzyme lecithin cholesterol acyltransferase (LCAT), whereas in the rare inherited disorder due to deficiency of LCAT virtually all of the plasma cholesterol is free. Likewise, the extent to which cholesterol is transported in plasma within high density lipoprotein (HDL) as opposed to low density lipoprotein (LDL) is an important determinant of the propensity to develop atherosclerotic coronary heart disease (CHD). The lower the level of HDL cholesterol, the more likely it is that this disease will occur prematurely, even if the total cholesterol is within the normal range. The opposite applies to LDL cholesterol, increased levels predisposing to premature death from CHD, as exemplified by familial hypercholesterolaemia. Measuring total cholesterol alone does not differentiate between free and esterified cholesterol, nor between HDL and LDL.
