What are LDL cholesterol particle size patterns A and B?

The LDL patterns A and B refer to the size of LDL cholesterol particles in the blood. Some doctors believe that small LDL cholesterol particles in the blood may pose a greater risk for developing atherosclerosis and heart attacks than the absolute level of LDL cholesterol in the blood. The size of LDL cholesterol particles is primarily inherited.

A special blood test called polyacrylamide gradient gel electrophoresis can measure particle size and determine whether a person has blood cholesterol LDL pattern A or LDL pattern B.

Persons with LDL cholesterol pattern A have large, buoyant LDL cholesterol particles. Individuals with pattern A are more likely to have normal blood levels of LDL cholesterol, HDL cholesterol, and triglycerides. Pattern A is usually not associated with an increased likelihood of atherosclerosis.

Persons with LDL cholesterol pattern B have predominantly small and dense LDL cholesterol particles. Pattern B is frequently associated with low HDL cholesterol levels, elevated triglyceride levels, and the tendency to develop high blood sugar levels and type II diabetes mellitus. Individuals with pattern B are also more likely to develop high blood triglyceride levels after a fatty meal (postprandial hyperlipidemia). Pattern B is associated with accelerated atherosclerosis and a 3 to 5- fold increase in heart attack risk. Pattern B is believed to be the most important cause of atherosclerosis in people with normal or near normal total and LDL cholesterol levels.

Some scientists believe that the smaller LDL particles are more dangerous than the larger ones because they can more easily squeeze through the tiny gaps between the cells in the endothelium to reach inside the artery walls. The endothelium is a thin layer of cells which covers the inner wall of the arteries. The cells making up the endothelium have tiny gaps between them. Others postulate that the smaller LDL cholesterol particles are more easily oxidized. Oxidation of cholesterol is significant in the formation of cholesterol plaques.

How can LDL cholesterol size be enlarged?

Even though LDL cholesterol particle size is mainly genetically inherited, individuals who have small LDL particles (pattern B) can increase their particle size through diet, exercise, and medications.

Diets that are low in saturated fat and cholesterol, regular aerobic exercise, and loss of excess body fat have been determined to decrease the number of small LDL particles and increase the number of large LDL particles in the blood. In other words, lifestyle modifications can change pattern B to pattern A.

When lifestyle changes alone are unsuccessful, medications can be used. Even though the statin medications (discussed below) are effective in lowering the absolute levels of LDL cholesterol, they appear to have a limited effect on LDL cholesterol size pattern. Medications such as nicotinic acid (niacin) and gemfibrozil (Lopid) have been found effective in many instances in increasing the size of LDL cholesterol particles.