What is (are) High Blood Cholesterol ? 

To understand high blood cholesterol (ko-LES-ter-ol), it helps to learn about cholesterol. Cholesterol is a waxy, fat-like substance thats found in all cells of the body.
                
Your body needs some cholesterol to make hormones, vitamin D, and substances that help you digest foods. Your body makes all the cholesterol it needs. However, cholesterol also is found in some of the foods you eat.
                
Cholesterol travels through your bloodstream in small packages called lipoproteins (lip-o-PRO-teens). These packages are made of fat (lipid) on the inside and proteins on the outside.
                
Two kinds of lipoproteins carry cholesterol throughout your body: low-density lipoproteins (LDL) and high-density lipoproteins (HDL). Having healthy levels of both types of lipoproteins is important.
                
LDL cholesterol sometimes is called bad cholesterol. A high LDL level leads to a buildup of cholesterol in your arteries. (Arteries are blood vessels that carry blood from your heart to your body.)
                
HDL cholesterol sometimes is called good cholesterol. This is because it carries cholesterol from other parts of your body back to your liver. Your liver removes the cholesterol from your body.
                
What Is High Blood Cholesterol?
                
High blood cholesterol is a condition in which you have too much cholesterol in your blood. By itself, the condition usually has no signs or symptoms. Thus, many people dont know that their cholesterol levels are too high.
                
People who have high blood cholesterol have a greater chance of getting coronary heart disease, also called coronary artery disease. (In this article, the term heart disease refers to coronary heart disease.)
                
The higher the level of LDL cholesterol in your blood, the GREATER your chance is of getting heart disease. The higher the level of HDL cholesterol in your blood, the LOWER your chance is of getting heart disease.
                
Coronary heart disease is a condition in which plaque (plak) builds up inside the coronary (heart) arteries. Plaque is made up of cholesterol, fat, calcium, and other substances found in the blood. When plaque builds up in the arteries, the condition is called atherosclerosis (ATH-er-o-skler-O-sis).
                
Atherosclerosis
                

                
Over time, plaque hardens and narrows your coronary arteries. This limits the flow of oxygen-rich blood to the heart.
                
Eventually, an area of plaque can rupture (break open). This causes a blood clot to form on the surface of the plaque. If the clot becomes large enough, it can mostly or completely block blood flow through a coronary artery.
                
If the flow of oxygen-rich blood to your heart muscle is reduced or blocked, angina (an-JI-nuh or AN-juh-nuh) or a heart attack may occur.
                
Angina is chest pain or discomfort. It may feel like pressure or squeezing in your chest. The pain also may occur in your shoulders, arms, neck, jaw, or back. Angina pain may even feel like indigestion.
                
A heart attack occurs if the flow of oxygen-rich blood to a section of heart muscle is cut off. If blood flow isnt restored quickly, the section of heart muscle begins to die. Without quick treatment, a heart attack can lead to serious problems or death.
                
Plaque also can build up in other arteries in your body, such as the arteries that bring oxygen-rich blood to your brain and limbs. This can lead to problems such as carotid artery disease, stroke, and peripheral artery disease.
                
Outlook
                
Lowering your cholesterol may slow, reduce, or even stop the buildup of plaque in your arteries. It also may reduce the risk of plaque rupturing and causing dangerous blood clots.
                

                
Sources: National Center for Health Statistics (20072010). National Health and Nutrition Examination Survey; National Center for Health Statistics (20052008). National Health and Nutrition Examination Survey; National Heart, Lung, and Blood Institute, National Cholesterol Education Program (2002). Third report of the National Cholesterol Education Program (NCEP) exert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III) final report.