What are LDLs?

Low-density lipoprotein (LDL) belongs to the lipoprotein particle family. Because LDLs transport cholesterol to the arteries and can be retained there by arterial proteoglycans starting the formation of plaques, increased levels are associated with atherosclerosis, and thus heart attack, stroke, and peripheral vascular disease. For this reason, cholesterol inside LDL lipoproteins is often called “bad” cholesterol. This is a misnomer. The cholesterol transported on LDL is the same as cholesterol transported on other lipoprotein particles. The cholesterol itself is not “bad”; rather, it is how and where the cholesterol is being transported, and in what amounts over time, that causes adverse effects.

Increasing evidence has revealed that the concentration and size of the LDL particles more powerfully relates to the degree of atherosclerosis progression than the concentration of cholesterol contained within all the LDL particles. The healthiest pattern, though relatively rare, is to have small numbers of large LDL particles and no small particles. Having small LDL particles, though common, is an unhealthy pattern; high concentrations of small LDL particles (even though potentially carrying the same total cholesterol content as a low concentration of large particles) correlates with much faster growth of atheroma, progression of atherosclerosis and earlier and more severe cardiovascular disease events and death.

The American Heart Association, NIH, and NCEP provide a set of guidelines for fasting LDL-Cholesterol levels, estimated or measured, and risk for heart disease. As of 2003, these guidelines were:

These guidelines were based on a goal of presumably decreasing death rates from cardiovascular disease to less than 2% to 3% per year or less than 20% to 30% every 10 years. Note that 100 is not considered optimal; less than 100 is optimal, though it is unspecified how much less.

Source: Wikipedia, January 28, 2008

What are HDLs?

High-density lipoproteins (HDL) form a class of lipoproteins that carry fatty acids and cholesterol from the body’s tissues to the liver. About thirty percent of blood cholesterol is carried by HDL.[1]

It is hypothesised that HDL can remove cholesterol from atheroma within arteries and transport it back to the liver for excretion or re-utilization—which is the main reason why HDL-bound cholesterol is sometimes called “good cholesterol”, or HDL-C. A high level of HDL-C seems to protect against cardiovascular diseases, and low HDL cholesterol levels (less than 40 mg/dL) increase the risk for heart disease.[1] When measuring cholesterol, any contained in HDL particles is considered as protection to the body’s cardiovascular health, in contrast to “bad” LDL cholesterol.

Epidemiological studies have shown that high concentrations of HDL (over 60 mg/dL) have protective value against cardiovascular diseases such as ischemic stroke and myocardial infarction. Low concentrations of HDL (below 40 mg/dL for men, below 50 mg/dL for women) are a positive risk factor for these atherosclerotic diseases.

Data from the landmark Framingham Heart Study showed that for a given level of LDL, the risk of heart disease increases 10-fold as the HDL varies from high to low. Conversely, for a fixed level of HDL, the risk increases 3-fold as LDL varies from low to high.

More sophisticated laboratory methods measure not just the total HDL but also the range of HDL particles, e.g. “lipoprotein subclass analysis”, typically divided into several groups by size, instead of just the total HDL concentration as listed above. The largest groups (most functional) of HDL particles have the most protective effects. The groups of smallest particles reflect HDL particles which are not actively transporting cholesterol, thus not protective.

Source: Wikipedia, January 28, 2008