Every person over the age of 20 should get their cholesterol levels checked at least every five years, as recommended by the National Cholesterol Education Program. Understanding the types of cholesterol and knowing your cholesterol numbers and ratios can help you monitor your risk for heart disease. This is important, because people with high blood cholesterol have twice the risk for heart disease as those with lower cholesterol levels.
Lipoproteins
The waxy nature of cholesterol, a type of lipid, makes it repel water, a scientific property known as hydrophobicity. Since blood consists mostly of water and cholesterol does not dissolve in water, cholesterol cannot travel through the blood on its own. The liver produces the majority of cholesterol in the body and also manufactures specialized proteins known as lipoproteins that bind to and carry cholesterol around the bloodstream. Lipoproteins contain protein on the outside with triglycerides, another lipid, and cholesterol on the inside. The two main types of lipoproteins are low-density lipoprotein -- LDL -- and high-density lipoprotein -- HDL.
LDL
LDL binds to cholesterol in the liver and carries it through the blood vessels to the cells. When the amount of cholesterol in the body increases, the amount of LDL also increases. Too much LDL in the blood vessels allows it to accumulate along their walls, forming plaque. The buildup of plaque makes the blood vessels thick and hard and restricts the flow of blood. Doctors recommend keeping your LDL levels as low as possible, striving to maintain an LDL of less than 100 mg/dL.
HDL
HDL binds to only one-third to one-fourth of the cholesterol in your body. This lipoprotein picks up cholesterol from the blood vessels and tissues and carries it back to the liver. The liver breaks down the cholesterol and uses it to produce bile acids -- a substance necessary for the digestion of dietary fat. Eventually the cholesterol gets excreted from the body along with the bile. Because HDL helps to remove cholesterol from the body, it has the distinction of being the "good" cholesterol, and higher levels of HDL are desirable. The National Heart Lung and Blood Institute recommends that men maintain HDL levels above 40 mg/dL or higher and women should aim for levels 50 mg/dL or higher.
Ratios
When comparing LDL to HDL, the smaller the ratio the better. For example, an LDL result of 100 mg/dL and a HDL result of 50 mg/dL calculates to a ratio of 2:1. As the LDL level goes lower and the HDL level rises, both trends have positive effects on heart disease risk. For an accurate measurement of your absolute LDL cholesterol, you must fast from everything but water for at least 12 hours prior to the blood test. In many cholesterol screenings this fails to occur, however. In a nonfasting test your doctor can still get a total cholesterol reading and your HDL cholesterol level. In this case your doctor may utilize another type of cholesterol ratio, the total cholesterol to HDL ratio, to assess your risk for heart disease. The Mayo Clinic suggests maintaining a LDL/HDL cholesterol ratio of 4:1 or lower, as higher ratios increase your risk for heart disease.
