Cholesterol is a chemical compound that is naturally produced by the body and is a combination of lipid (fat) and steroid. Cholesterol is a building block for cell membranes and for hormones like estrogen and testosterone. About 80% of the body's cholesterol is produced by the liver, while the rest comes from our diet. . 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, dietary cholesterol is absorbed from the intestine and stored in the liver. The liver is able to regulate cholesterol levels in the blood stream and can secrete cholesterol if it is needed by the body.
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.
Both heredity and diet have a significant influence on a person's LDL, HDL and total cholesterol levels. For example, familial hypercholesterolemia (hyper= more + cholesterol + emia= in blood) 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.
Therapeutic lifestyle changes to lower LDL cholesterol involves losing excess weight, exercising regularly, and following a diet that is low in saturated fat and cholesterol.
Medications to lower cholesterol
Medications are prescribed when lifestyle changes cannot reduce the LDL cholesterol to desired levels. The most effective and widely used medications to lower LDL cholesterol are called statins. Most of the large controlled trials that demonstrated the heart attack and stroke prevention benefits of lowering LDL cholesterol used one of the statins. Other medications used in lowering LDL cholesterol and in altering cholesterol profiles include nicotinic acid (niacin), fibrates such as gemfibrozil (Lopid), resins such as cholestyramine (Questran), and ezetimibe, Zetia.
What are "normal" cholesterol blood levels?
There are no established “normal” blood levels for total and LDL cholesterol. In most other blood tests in medicine, normal ranges can be set by taking measurements from large number of healthy subjects. The normal range of LDL cholesterol among “healthy” adults (adults with no known coronary heart disease) in the United States may be too high. The atherosclerosis process may be quietly progressing in many healthy children and adults with average LDL cholesterol blood levels, putting them at risk of developing coronary heart diseases in the future.
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 manufactures and secretes LDL cholesterol into the blood. It also removes LDL cholesterol from the blood by active LDL receptors on the surface of its cells. A decrease number of liver cell 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 (hyper= more + cholesterol + emia= in blood) 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.
Does lowering LDL cholesterol prevent heart attacks and strokes?
Lowering LDL cholesterol is currently one of the primary public health initiatives preventing atherosclerosis and heart attacks. The benefits of lowering LDL cholesterol include:- reducing or stopping the formation of new cholesterol plaques on the artery walls;
- reducing existing cholesterol plaques on the artery walls and widening the arteries;
- preventing the rupture of cholesterol plaques, which initiates blood clot formation and blocks blood vessels;
- decreasing the risk of heart attacks; and
- decreasing the risk of strokes.
How can LDL cholesterol levels be lowered?
Therapeutic lifestyle changes to lower cholesterolTherapeutic lifestyle changes to lower LDL cholesterol involves losing excess weight, exercising regularly, and following a diet that is low in saturated fat and cholesterol.
Medications to lower cholesterol
Medications are prescribed when lifestyle changes cannot reduce the LDL cholesterol to desired levels. The most effective and widely used medications to lower LDL cholesterol are called statins. Most of the large controlled trials that demonstrated the heart attack and stroke prevention benefits of lowering LDL cholesterol used one of the statins. Other medications used in lowering LDL cholesterol and in altering cholesterol profiles include nicotinic acid (niacin), fibrates such as gemfibrozil (Lopid), resins such as cholestyramine (Questran), and ezetimibe, Zetia.
What are "normal" cholesterol blood levels?
There are no established “normal” blood levels for total and LDL cholesterol. In most other blood tests in medicine, normal ranges can be set by taking measurements from large number of healthy subjects. The normal range of LDL cholesterol among “healthy” adults (adults with no known coronary heart disease) in the United States may be too high. The atherosclerosis process may be quietly progressing in many healthy children and adults with average LDL cholesterol blood levels, putting them at risk of developing coronary heart diseases in the future.
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