What Are Good And Bad Cholesterol?

While there is in reality only one type of cholesterol, LDL and HDL lipoproteins transport blood cholesterol in different ways, resulting in the common labels of good and bad.

While the most common belief concerning cholesterol in the blood is uniformly that it is bad, a rather large number of qualifications should be made to this statement. Cholesterol is in fact produced by the body (to a much greater degree than it is gained through digestion), and is absolutely necessary to the synthesis of cell membranes as it allows those cells to remain structurally stable within a greater range of temperatures, among its other physiological uses. Cholesterol is synthesized in and secreted by the liver, where it is, with bile, excreted to the stomach and reabsorbed by the small intestine, where it is then transported to the liver via the blood.

Most blood cholesterol is synthesized, and not taken in through consumption, so while it was previously thought that eating less cholesterol would produce lower levels of blood cholesterol, this may not be true, namely because the body's level of production varies according to observed levels in the blood in what is called a homeostatic process.

It has received a bad name, so to speak, within the discussion of atherosclerosis, a form of heart disease which involves the buildup of atheroma plaque upon the body's arterial walls, a process which in certain situations the presence of cholesterol promotes. In this context, cholesterol has been identified as "bad" or "good", as it relates to two varieties of lipoproteins, low density lipoprotein (LDL) and high density lipoprotein (HDL).

Cholesterol is a lipid, or fatty molecule, which makes it poorly soluble in water. Lipoproteins bond with lipids like cholesterol to make them water soluble, allowing them to travel through the blood to where they are required. Low density lipoprotein and high density lipoprotein are not, in fact, types of cholesterol, and they do carry the exact same type of cholesterol (being that there is only one).

Medicine has indicated that levels of low density lipoprotein disproportionately high, as compared to the body's levels of high density lipoprotein, can promote the buildup of atheroma plaque in the aterties. High levels of high density lipoprotein, on the other hand, seem to slow or even reverse the rate of buildup of arterial plaque.

Most treatments for atherosclerosis tend to involve changing the way this buildup is transported by low density lipoprotein and high density lipoprotein or to change the levels of these proteins present, rather than attempting to lower overall cholesterol levels. However, as trends indicate that lower overall levels of cholesterol tend an individual toward decreased risk of heart disease, medications may also aim to achieve this goal. Some newer studies and human trials have attempted to verify the usefulness of synthetic human HDL as applied to patients with atherosclerosis, and positive results have been indicated.

For reference, the level of LDL determined to be "desirable" is in the range of 75-130 mg/dl, with a ratio to HDL of less than 5:1. Desirable levels may vary by association, and a physician is one's best source for information and advice on matters of blood cholesterol.

© Demand Media 2011