An Introduction to Cholesterol

Cholesterol-Carrying Lipoproteins. These are the lipoproteins commonly referred to as cholesterol.

• Low density lipoproteins (LDL). (Often called the "bad" cholesterol.)
• High-density lipoproteins (HDL), the smallest and most dense. (Referred to as the "good" cholesterol.)

Triglyceride-Carrying Lipoproteins.

• Intermediate density lipoproteins (IDL). They tend to carry triglycerides.
• Very low density lipoproteins (VLDL). These tend to carry triglycerides.
• Chylomicrons (largest in size and lowest in density).

Lipoprotein(a). Lipoprotein(a), or lp(a) has a size and density somewhere between LDL and HDL. The molecules carry a protein that may interfere with the body's ability to dissolve blood clots. Lipoprotein(a) is being investigated as a possible marker or cause of heart disease.

Remnant Lipoproteins. Remnant lipoproteins are byproducts of chylomicrons, very low-density lipoproteins (VLDL), or both. Some research indicates that high levels may be an important risk factor for coronary artery disease, particularly in patients who have otherwise normal cholesterol levels.

Cholesterol Guidelines

Reducing LDL and total cholesterol levels, while at the same time boosting HDL levels, can prevent heart attacks and death in all people (with or without heart disease). Reducing LDL is the primary goal of most cholesterol therapy.

Blood tests can easily measure both HDL and overall cholesterol levels. It is very difficult to measure LDL levels by themselves, but LDL levels can be reliably calculated by subtracting HDL and triglyceride levels from total cholesterol. The exact formula is:

LDL = TOTAL CHOLESTEROL - HDL - TRIGLYCERIDES/5.

In 2004, the National Cholesterol Education Program updated its clinical practice guidelines. The new recommendations set lower treatment goals for LDL levels based on a patient's risk factors for heart disease.

The risk factors include:

• Having a first-degree female relative diagnosed with heart disease before age 65 or a first-degree male relative diagnosed before age 55
• Being male and over age 45 or female and over age 55
• Cigarette smoking
• Diabetes
• High blood pressure
• Metabolic syndrome (risk factors associated with obesity such as low HDL levels and high triglycerides)