How does high cholesterol cause heart disease?

High LDL (or bad) cholesterol leads to heart disease by contributing to a condition known as atherosclerosis. Atherosclerosis is a build up of plaque in the wall of the artery. In areas of damage to the walls of the arteries (often caused by other risk factors like high blood pressure, diabetes, or smoking) cholesterol plaque can build up. If the build up is severe enough, it can cause a decrease in blood flow -- this can lead to heart attack and stroke. Lowering LDL cholesterol, as well as treating other risk factor like high blood pressure, diabetes and smoking, can reduce the risk of heart attack and stroke.

The more low-density lipoproteins (LDL) or bad cholesterol in your bloodstream, the greater your heart risk. The National Cholesterol Education Program (NCEP), a division of the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH), has been evaluating the evolving medical evidence and issuing cholesterol guidelines for several decades. The current guidelines identify LDL levels below 100 milligrams per deciliter (mg/dL) as optimal; those 100 to 129 as near to above optimal; 130 to 159 as borderline high; 160 to 189 as high, and greater than 190 as very high.

By contrast, the more high-density lipoproteins (HDL) or good cholesterol in your bloodstream, the lower your chances of having a heart attack. Findings from the Framingham Heart Study (a long-running landmark study of factors contributing to heart disease) and elsewhere suggest that every one-point rise in HDL lowers the risk for heart attack 2% to 3%. The NCEP guidelines consider levels of 60 mg/dL or above as protective against heart disease, while levels below 40 mg/dL increase your risk.

High cholesterol is a major risk factor for heart disease. Risk factors such as high blood pressure, cigarette smoking, and diabetes can cause damage to the lining of blood vessels in the heart allowing circulating cholesterol to penetrate the lining of these blood vessels. Like a splinter under your skin, cholesterol particles that are retained in the lining of heart arteries can lead to inflammation and plaque formation. In people at risk this process usually starts early in adulthood and progresses over time. As heart artery plaque grows it can limit blood flow to the heart. This can lead to a heart attack, heart failure, angina and death. Addressing one's cardiac risk factors and lowering blood cholesterol levels can reduce an individual's risk for heart disease. If diet and exercise do not bring blood cholesterol levels to normal levels, cholesterol lowering medication may be needed.

Cholesterol is a fatty substance in your blood. It can build up inside your arteries and block the blood flow to your heart or brain.

Elevated levels of the type of cholesterol called low-density lipids (LDL) have been strongly associated with the development of blockages in the arteries that supply the heart with blood. These blockages are called plaques. They are made up of fatty substances and calcium. These plaques are what cause heart attacks.

Heart Disease can be roughly divided between coronary (vascular) disease and non-coronary (structural) disease of the heart. Often chronic vascular disease can lead to structural problems of the heart. In terms of coronary disease, cholesterol and plaque formation in the form of atheroma formation leads to occlusion of the coronary arteries. Cholesterol is an important factor, along with vascular inflammation and hypercoagulability that can lead to coronary occlusion. All these factors can have genetic determinants and environmental determinants that may be modifiable or determine a person's risk.

If you have high cholesterol, fatty substances build up in your blood vessels and arteries. This leads to a hardening of the arteries and decreased blood flow. Without as much blood flow, the heart has less oxygen. Low oxygen levels and blood circulation tend to cause heart diseases and conditions like atherosclerosis, heart attack, and stroke.

The nicknames "good" and "bad" cholesterol relate to risk factors for heart disease. High levels of high density lipoproteins (HDL), or "good" cholesterol, are linked to lower heart disease risk; high levels of low density lipoproteins (LDL), or "bad" cholesterol, are associated with higher heart disease risk. Remember, keep you HDL levels High and your LDL levels Low.

Coronary heart disease (CHD) appears to be directly related to the amount of lipids (fats and fat-like substances) in the blood. That's because atherosclerosis, a fatty buildup in the cells lining the walls of arteries -- in this case, the coronary arteries to the heart itself -- narrows the diameter of these blood vessels and decreases blood flow, sometimes to a critical point.

Cholesterol is the main culprit in this buildup. The problem occurs when you have a lot of the wrong kind of cholesterol -- low-density lipoprotein (LDL) cholesterol -- which can clog the arteries. If you have a lot of the healthy kind of cholesterol -- high-density lipoprotein (HDL) cholesterol -- it can make a big difference in your risk of heart disease. Because HDL rids the body of excess LDL, the ratio of total cholesterol to HDL is very important. The amount of HDL itself or the ratio of total cholesterol to HDL often is a better predictor of the likelihood of heart disease than total cholesterol alone. If HDL is low (less than 35 mg/dL) and the ratio is high, the risk of heart disease increases, even when total cholesterol is not that high. (As many as 20% of men who have CHD follow that pattern.) In older women (especially those taking estrogen), it is not uncommon to find high levels of cholesterol that are not associated with a higher risk of heart disease because levels of HDL are also high (60 mg/dL or higher). Experts have defined "borderline-high" cholesterol as 200-239 mg/dL and "high" cholesterol as 240 mg/dL or higher.

High cholesterol is diagnosed most often by a blood test called a lipid panel. A lipid panel is a blood test that measures the amounts of different types of fat carried in specialized particles in your bloodstream. The panel reports total cholesterol (a fatty substance carried in the blood by particles called lipoproteins), triglycerides (a manufactured fat that is an important part of fatty particles made by your liver that help deliver fuel to your muscles and help store fuel in fatty tissue to help you to survive in case of starvation), HDL cholesterol (the amount of cholesterol carried by HDL particles, which are involved in eliminating excess cholesterol from the blood vessel walls throughout the body) and LDL cholesterol (the amount of cholesterol carried by LDL particles, which are involved in delivering cholesterol to tissues throughout the body to make membranes around your cells, making hormones that are necessary for normal sexual development, aiding in salt and water balance, making vitamins and making bile to help us to digest our food). The lipid panel is one factor that helps your doctor to determine whether you are prone to future risk of hardening of the arteries, a process known as coronary atherosclerosis.
This condition may lead to heart attack (death of a part of the heart muscle), need for a coronary stent (a mesh sleeve that can be used in selected patients to open an artery for a person who is experiencing chest pain or shortness of breath upon exertion), coronary bypass surgery (an operation in which a heart surgeon uses arteries or veins to re-route blood around narrowings in the arteries supplying blood to the heart muscle) or sudden cardiac death. Results of the lipid panel are also used to help to guide physicians to make medical decisions as to how to use diet, exercise and medication to help to prevent future heart attacks.

About one in five Americans has high blood cholesterol (more than 240 milligrams per deciliter), according to the American Heart Association, which doubles their risk of heart attack compared with those whose cholesterol levels are below 200 milligrams per deciliter. Reducing your cholesterol by a mere 10 percent at age 40 can lower your heart attack risk by 50 percent; at age 50, by 40 percent; at age 60, by 30 percent; and at age 70, by 20 percent.

Before tackling how to lower cholesterol, it’s important to understand what it is and how it works in the body. To begin with, cholesterol is a structural component in every cell membrane throughout the body; it maintains nerve integrity, facilitates hormone production and keeps cell walls strong. The body produces the amount of cholesterol it needs, but dietary factors can heavily increase its production, and of course, too much cholesterol circulating in the blood (serum cholesterol) can clog the arteries, elevating the risk of both heart attack and stroke. Cholesterol is transported to and from the cells by specific “carrier” proteins, referred to as low-density lipoproteins (LDL) and high-density lipoproteins (HDL). LDL is carried by the former to the blood and tissues, while HDL is carried by the latter out of the blood and back to the liver to be broken down, which is why moderate increases in this type of cholesterol are seen as healthy.

While some dietary fats can raise blood-cholesterol levels, there does not seem to be a simple relationship between dietary cholesterol and blood cholesterol. Dietary Guidelines for Americans, 2005 recommends keeping cholesterol obtained from food to less than 300 milligrams per day (the amount found in two small eggs). Findings from a University of Connecticut study published in Metabolism suggest that while egg cholesterol raises levels of certain less dangerous LDL molecules, it has virtually no effect on those smallest, densest LDL particles most closely linked with heart damage.

When there is too much cholesterol (a fat-like substance) in your blood, it builds up in the walls of your arteries. Over time, this buildup causes "hardening of the arteries" so that arteries become narrowed and blood flow to the heart is slowed down or blocked. The blood carries oxygen to the heart, and if enough blood and oxygen cannot reach your heart, you may suffer chest pain. If the blood supply to a portion of the heart is completely cut off by a blockage, the result is a heart attack.

High blood cholesterol itself does not cause symptoms, so many people are unaware that their cholesterol level is too high. It is important to find out what your cholesterol numbers are because lowering cholesterol levels that are too high lessens the risk for developing heart disease and reduces the chance of a heart attack or dying of heart disease, even if you already have it. Cholesterol lowering is important for everyone –younger, middle age, and older adults; women and men; and people with or without heart disease.

This answer from the National Heart, Lung, and Blood Institute has been reviewed and/or edited by Dr. Robert S. Kaufmann.