An increased level of HDL cholesterol is associated with a lower risk of coronary heart disease (CHD). Conversely, low levels of HDL cholesterol are associated with an increased risk. This is why HDL is thought of as the "good" type of cholesterol.
However, it seems that it is not actually the cholesterol itself that is “good”, but the lipoprotein which carries it – in other words, high-density lipoprotein (HDL).
It appears that the HDL molecule itself can clean out excess cholesterol – including that which came from the “bad” LDL cholesterol which has accumulated in the walls of arteries – and take it back to the liver for reprocessing. It also performs antioxidant activities, which help protect arteries against atherosclerosis, the cause of CHD.
Low-density lipoprotein (LDL) is very rich in cholesterol and, in excess, is the main cause of coronary and other artery disease.
Most of the cholesterol in the blood is carried in LDL, so your total cholesterol level is a reflection of the amount of LDL cholesterol in your blood.
While other lipoproteins are removed within hours or minutes, LDL remains in the bloodstream for nearly three days. But eventually it’s cleared, mostly by the liver.
The basic principle is simple: LDL is linked to another protein, called apoB. This recognises a specific receptor (LDL-R) on liver cell walls to which it docks before being taken into the liver cells.
The mechanism is important since it can be genetically faulty (a common occurrence among South Africans), leading to the heavy accumulation of LDL in the bloodstream and giving rise to the inherited disorder of familial hypercholesterolaemia.
When levels of LDL are high, the lipoprotein penetrates the lining of the blood vessels, leading to the development of atherosclerosis.
This build-up of atherosclerotic plaque causes narrowing of the arteries, a situation that can lead to a heart attack and stroke, among other complications.
Raised total cholesterol – reflected by raised LDL levels – is a major risk factor for heart disease and stroke.