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Lipids are a wide-ranging group of organic compounds found in all living organisms, including humans,
plants, and animals. Lipids are the body's reserve supply of energy. Unlike other organic compounds, lipids are soluble in alcohol, ether, and other organic substances but not in water.
Lipid comes from the Greek word lipos, meaning fat. Cells make lipids in the human body and, along with carbohydrates and proteins, are components of all life. Among the major classes of lipids in humans are acids, glycerol-derived lipids (including fats and oils), and steroids. The two major lipids found in the blood are cholesterol and triglycerides.
Cholesterol is a lipid that is essential for repairing cell membranes, manufacturing vitamin D on the skin's surface, and creating hormones, especially testosterone and estrogen. To circulate in the bloodstream, cholesterol must attach to proteins. The combination of cholesterol and protein is called lipoprotein.
The two major lipoprotein groups are high-density lipoprotein (HDL), commonly referred to as "good" cholesterol, and low-density lipoprotein (LDL), also known as "bad" cholesterol. HDL helps prevent fat buildup throughout the body by carrying cholesterol from the arteries to the liver, where it is disposed of. LDL carries most of the cholesterol in the body, so an excess of LDL can clog the arteries with cholesterol buildup.
High levels of LDL are 100 milligrams or more per deciliter (mg/dL) of blood for people with heart or vascular disease or diabetes, 160 mg/dL for people with two risk factors, and 190 mg/dL or more for people with no risk factors. A high LDL level is a primary cause of coronary heart disease (CHD) and stroke. This is because when LDL accumulates in the body, it forms a plaque that sticks to the walls of arteries, slowing or restricting blood flow and oxygen delivery to the heart and other vital organs. This causes atherosclerosis, commonly referred to as hardening of the arteries. The buildup of plaque usually occurs over a few years and without cholesterol tests the patient may not know about the problem until angina (chest pains) or an acute myocardial infarction (heart attack) occurs.
Among the key risk factors for high LDL are age, gender, smoking, diabetes, and a family history of the disorder. About 25% of people with high LDL can control the disorder with a diet low in saturated fats and cholesterol, weight control, and regular exercise. About 75% of people with high LDL require lipid-lowering medications in addition to the weight, diet, and exercise guidelines. First-line drugs recommended by the National Cholesterol Education Program to treat high LDL are bile acid sequestrants such as cholestyramine (Questran) and colestipol (Colestid), niacin (either over-the-counter or time-released prescription drugs such as Niaspan, Slo-Niacin, and Nicobid), and HMG-CoA reductase inhibitors, including fluvastatin (Lescol), pravastatin (Pravachol), cervistatin (Baycol), lovastatin (Mevacor), simvastatin (Zocor), and atorvastatin (Lipitor). The second-line drug choice are fibric acid derivatives such as gemfibrozil, clofibrate, and fenofibrate (Tricor.) Estrogen replacement therapy should also be considered as complementary therapy in post-menopausal women.
Levels of HDL between 30 and 75 mg/dL are associated with decreased risk of CHD and stroke. But HDL levels under 30 mg/dL are associated with a greater risk for CHD and stroke.
Author Info: Ken R. Wells, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Nursing and Allied Health, 2002This feature is for informational purposes only and should not be used to replace the care and information received from your healthcare provider. Please consult a healthcare professional with any health concerns you may have.
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