What Do Those Cholesterol Numbers Mean?

When you have your cholesterol levels tested, you’ll probably get two sets of numbers.

LDL stands for low-density lipoprotein, and HDL means high-density lipoprotein. Both carry fats in the blood, but to different places and for different purposes.

LDL delivers triglycerides and cholesterol from the liver to the body by way of the arteries. Excess LDL and triglycerides in the blood increase the risk of plaque formation in the arteries.

In contrast, HDL “soaks up” excess cholesterol from the tissues and returns it to the liver for disposal from the body.

High levels of LDL cholesterol in the blood are a sign of increased risk of heart attack, but high levels of HDL cholesterol are associated with lower risk.

How much is too much or too little? As a general rule, total cholesterol should be less than 200 milligrams/deciliter (mg/dl) of blood. LDL cholesterol should be less than 130 mg/dl and HDL cholesterol 35 mg/dl or higher. If your cholesterol levels are outside these ranges, see your doctor for a personalized treatment plan, which may include cholesterol-lowering medication. Even with cholesterol-lowering drugs, you need to adopt heart-healthy life habits. These will help bring a larger drop in your blood cholesterol levels and reduce your risk of heart attack and other chronic diseases.

The good news is that you can help raise your HDL cholesterol, the good cholesterol, by exercising, by losing weight if you’re overweight, and by quitting smoking if you smoke.

Definition of Cholesterol

What is cholesterol?

Cholesterol is a fatty substance (a lipid) that is an important part of the outer lining (membrane) of cells in the body of animals. Cholesterol is also found in the blood circulation of humans. The cholesterol in a person's blood originates from two major sources; dietary intake and liver production. Dietary cholesterol comes mainly from meat, poultry, fish, and dairy products. Organ meats, such as liver, are especially high in cholesterol content, while foods of plant origin contain no cholesterol. After a meal, cholesterol is absorbed by the intestines into the blood circulation and is then packaged inside a protein coat. This cholesterol-protein coat complex is called a chylomicron.

The liver is capable of removing cholesterol from the blood circulation as well as manufacturing cholesterol and secreting cholesterol into the blood circulation. After a meal, the liver removes chylomicrons from the blood circulation. In between meals, the liver manufactures and secretes cholesterol back into the blood circulation.

What are LDL and HDL cholesterol?

LDL cholesterol is called "bad" cholesterol, because elevated levels of LDL cholesterol are associated with an increased risk of coronary heart disease. LDL lipoprotein deposits cholesterol on the artery walls, causing the formation of a hard, thick substance called cholesterol plaque. Over time, cholesterol plaque causes thickening of the artery walls and narrowing of the arteries, a process called atherosclerosis.

HDL cholesterol is called the "good cholesterol" because HDL cholesterol particles prevent atherosclerosis by extracting cholesterol from the artery walls and disposing of them through the liver. Thus, high levels of LDL cholesterol and low levels of HDL cholesterol (high LDL/HDL ratios) are risk factors for atherosclerosis, while low levels of LDL cholesterol and high level of HDL cholesterol (low LDL/HDL ratios) are desirable.

Total cholesterol is the sum of LDL (low density) cholesterol, HDL (high density) cholesterol, VLDL (very low density) cholesterol, and IDL (intermediate density) cholesterol.

What determines the level of LDL cholesterol in the blood?

The liver not only manufactures and secretes LDL cholesterol into the blood; it also removes LDL cholesterol from the blood. A high number of active LDL receptors on the liver surfaces is associated with the rapid removal of LDL cholesterol from the blood and low blood LDL cholesterol levels. A deficiency of LDL receptors is associated with high LDL cholesterol blood levels.

Both heredity and diet have a significant influence on a person's LDL, HDL and total cholesterol levels. For example, familial hypercholesterolemia (FH) is a common inherited disorder whose victims have a diminished number or nonexistent LDL receptors on the surface of liver cells. People with this disorder also tend to develop atherosclerosis and heart attacks during early adulthood.

Diets that are high in saturated fats and cholesterol raise the levels of LDL cholesterol in the blood. Fats are classified as saturated or unsaturated (according to their chemical structure). Saturated fats are derived primarily from meat and dairy products and can raise blood cholesterol levels. Some vegetable oils made from coconut, palm, and cocoa are also high in saturated fats.

Lowering LDL cholesterol is currently the primary focus in preventing atherosclerosis and heart attacks.