Wednesday, December 3, 2008



AHA Scientific Position

Cholesterol is a soft, waxy substance found among the lipids (fats) in the bloodstream and in all your body's cells. It's an important part of a healthy body because it's used to form cell membranes, some hormones and is needed for other functions. But a high level of cholesterol in the blood — hypercholesterolemia — is a major risk factor for coronary heart disease, which leads to heart attack.

Cholesterol and other fats can't dissolve in the blood. They have to be transported to and from the cells by special carriers called lipoproteins. There are several kinds, but the ones to focus on are low-density lipoprotein (LDL) and high-density lipoprotein (HDL).

What is LDL cholesterol?

Low-density lipoprotein is the major cholesterol carrier in the blood. If too much LDL cholesterol circulates in the blood, it can slowly build up in the walls of the arteries feeding the heart and brain. Together with other substances it can form plaque, a thick, hard deposit that can clog those arteries. This condition is known as atherosclerosis. A clot (thrombus) that forms near this plaque can block the blood flow to part of the heart muscle and cause a heart attack. If a clot blocks the blood flow to part of the brain, a stroke results. A high level of LDL cholesterol (160 mg/dL and above) reflects an increased risk of heart disease. If you have heart disease, your LDL cholesterol should be less than 100 mg/dL and your doctor may even set your goal to be less than 70 mg/dL. That's why LDL cholesterol is called "bad" cholesterol. Lower levels of LDL cholesterol reflect a lower risk of heart disease.

What is HDL cholesterol?

About one-third to one-fourth of blood cholesterol is carried by HDL. Medical experts think HDL tends to carry cholesterol away from the arteries and back to the liver, where it's passed from the body. Some experts believe HDL removes excess cholesterol from plaques and thus slows their growth. HDL cholesterol is known as "good" cholesterol because a high HDL level seems to protect against heart attack. The opposite is also true: a low HDL level (less than 40 mg/dL in men; less than 50 mg/dL in women) indicates a greater risk. A low HDL cholesterol level also may raise stroke risk.

What is Lp(a) cholesterol?

Lp(a) is a genetic variation of plasma LDL. A high level of Lp(a) is an important risk factor for developing atherosclerosis prematurely. How an increased Lp(a) contributes to heart disease isn't clear. The lesions in artery walls contain substances that may interact with Lp(a), leading to the buildup of fatty deposits.

What about cholesterol and diet?

People get cholesterol in two ways. The body — mainly the liver — produces varying amounts, usually about 1,000 milligrams a day. Foods also can contain cholesterol. Foods from animals (especially egg yolks, meat, poultry, shellfish and whole- and reduced-fat milk and dairy products) contain it. Foods from plants (fruits, vegetables, grains, nuts and seeds) don't contain cholesterol.

Typically the body makes all the cholesterol it needs, so people don't need to consume it. Saturated fatty acids are the main culprit in raising blood cholesterol, which increases your risk of heart disease. Trans fats also raise blood cholesterol. But dietary cholesterol also plays a part. The average American man consumes about 337 milligrams of cholesterol a day; the average woman, 217 milligrams.

Some of the excess dietary cholesterol is removed from the body through the liver. Still, the American Heart Association recommends that you limit your average daily cholesterol intake to less than 300 milligrams. If you have heart disease, limit your daily intake to less than 200 milligrams. Still, everyone should remember that by keeping their dietary intake of saturated and trans fats low, they can significantly lower their dietary cholesterol intake. Foods high in saturated fat generally contain substantial amounts of dietary cholesterol.

People with severe high blood cholesterol levels may need an even greater reduction. Since cholesterol is in all foods from animal sources, care must be taken to eat no more than six ounces of lean meat, fish and poultry per day and to use fat-free and low-fat dairy products. High-quality proteins from vegetable sources such as beans are good substitutes for animal sources of protein.

How does physical activity affect cholesterol?

Regular physical activity increases HDL cholesterol in some people. A higher HDL cholesterol is linked with a lower risk of heart disease. Physical activity can also help control weight, diabetes and high blood pressure. Aerobic physical activity raises your heart and breathing rates. Regular moderate-to-vigorous-intensity physical activity such as brisk walking, jogging and swimming also condition your heart and lungs.

Physical inactivity is a major risk factor for heart disease. Even moderate-intensity activities, if done daily, help reduce your risk. Examples are walking for pleasure, gardening, yard work, housework, dancing and prescribed home exercise.

How does tobacco smoke affect cholesterol?

Tobacco smoke is one of the six major risk factors of heart disease that you can change or treat. Smoking lowers HDL cholesterol levels and increases the tendency for blood to clot.

How does alcohol affect cholesterol?

In some studies, moderate use of alcohol is linked with higher HDL cholesterol levels. However, because of other risks, the benefit isn't great enough to recommend drinking alcohol if you don't do so already.

If you drink, do so in moderation. People who consume moderate amounts of alcohol (an average of one to two drinks per day for men and one drink per day for women) have a lower risk of heart disease than nondrinkers. However, increased consumption of alcohol brings other health dangers, such as alcoholism, high blood pressure, obesity, stroke, cancer, suicide, etc. Given these and other risks, the American Heart Association cautions people against increasing their alcohol intake or starting to drink if they don't already do so. Consult your doctor for advice on consuming alcohol in moderation.

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