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What is HDL cholesterol (high density lipoproteins)?
High density lipoproteins (HDL) form a class of lipoproteins, varying somewhat in their size and contents, that carry cholesterol from the body's tissues to the liver. HDL cholesterol makes up a smaller portion of the cholesterol carriers. However, HDLs are probably just as, if not more important than LDLs in preventing heart disease. HDL removes cholesterol from the blood by carrying it to the liver where it is metabolized. Therefore, it is beneficial to have high levels of high density lipoproteins in the blood.
Because high density lipoproteins can remove cholesterol from atheroma within arteries, and transport it back to the liver for excretion, they are seen as "good" lipoproteins. When measuring cholesterol, any contained in HDL particles serves as protection to the body's cardiovascular health. (In contrast to "bad" low-density lipoprotein cholesterol.)
HDL are the smallest of the lipoproteins. They are the densest because they contain the highest proportion of protein. The liver synthesises these lipoproteins as empty flattened spherical protein particles. They are capable of picking up cholesterol, carried internally, from cells they interact with. They increase in size as they circulate through the bloodstream, if they internal more cholesterol molecules. Thus it is the concentration of large high density lipoproteins particles which more accurately reflects protective action, as opposed to the concentration of total high density lipoproteins particles. This ratio of large high density lipoproteins to total HDL particles varies widely and is only measured by more sophisticated lipoprotein assays using either electrophoresis, the orignial method developed in the 1970s or newer NMR spectroscopy methods, developed in the 1990s.
Men tend to have noticeably lower HDL levels, with smaller size & lower cholesterol content, than women. Men also have an increased incidence of atherosclerotic heart disease. Epidemiological studies have shown that high concentrations of high density lipoproteins (over 60 mg/dL) have protective value against cardiovascular diseases (such as ischemic stroke and myocardial infarction). Low concentrations of HDL (below 40 mg/dL for men, below 50 mg/dL for women) are a positive risk factor for these atherosclerotic diseases.
More information on cholesterol
What is cholesterol? - Cholesterol is a steroid lipid, found in the cell membranes of all body tissues, and transported in the blood plasma, of all animals.
What is LDL cholesterol? - Low-density lipoprotein (or "bad") cholesterol carries the largest amount of cholesterol in the blood and is responsible for depositing cholesterol in the artery walls. An elevated LDL cholesterol level is associated with a greater risk of heart disease.
Why is LDL cholesterol considered "bad"? - When too much LDL cholesterol circulates in the blood, it can slowly build up in the inner walls of the arteries that feed the heart and brain.
What is HDL cholesterol? - High-density lipoprotein (HDL) cholesterol is one of several types of fats and is measured as 'Total Cholesterol'. HDL is thought to pick up cholesterol from body tissues and bring it back to the liver for reprocessing or excretion.
Why is HDL cholesterol considered "good"? - Because HDL clears cholesterol out of the system and high levels of it are associated with a decreased risk of heart disease, HDL is often called "good" cholesterol.
How to raise HDL Cholesterol (good cholesterol)? - Regular aerobic exercise, loss of excess weight (fat), and cessation of cigarette smoking cigarettes will increase HDL cholesterol levels.
How cholesterol is measured and tested? - Cholesterol is measured in units called millimoles per litre of blood, usually shortened to "mmol/litre" or "mmol/l".
What're the cholesterol readings? - Cholesterol readings you receive from your medical provider generally include total cholesterol, LDL cholesterol, and high density lipoproteins cholesterol levels.
How often should my cholesterol be checked? - According to a new set of national guidelines governing cholesterol measurement and treatment, it is recommended that the level be treated every 5 years.
What causes high cholesterol? - High cholesterol is caused by eating a diet that is high in saturated fats and cholesterol. Some people, however, have an inherited disorder in which the body cannot properly metabolize cholesterol.
What are the high cholesterol risk factors? - A diet high in certain types of fats is one factor. Medical problems such as poorly controlled diabetes, an underactive thyroid gland, an overactive pituitary gland, liver disease or kidney failure also may cause high cholesterol levels.
What're the symptoms of high cholesterol? - People with severely elevated cholesterol may have fat deposits in tendons and skin, liver and spleen enlargement, and abdominal pain if pancreatitis develops.
What are triglycerides? - Triglycerides are another type of fat that is associated with adverse health consequences. Many patients with high cholesterol also have high triglycerides.
How to test triglycerides? - For triglycerides testing, blood is drawn from a vein in the arm. A vein at the inside of the elbow or on the back of the hand is usually selected.
How can LDL cholesterol levels be lowered? - Lowering low-density lipoprotein cholesterol involves losing excess weight, exercising regularly, and following a diet that is low in saturated fat and cholesterol.
How to reduce cholesterol with dietary therapy? - A low-fat, low-cholesterol diet is desired to keep your total fat consumption--saturated, polyunsaturated and monounsaturated--to fewer than 30 percent of your daily intake of calories.
What about when I go out to eat? - Avoid fried foods. Entrees covered with sauces, as well as creamy dressing, thick soups and casseroles should be avoided because they are usually rich in fat. Look for items labeled "heart-healthy" on the menu.
What cholesterol medications are available to lower cholesterol? - Cholesterol-reducing drugs include cholestyramine (Questran), colestipol (Colestid), gemfibrozil (Lopid), lovastatin (Mevacor), pravastatin (Pravachol) and simvastatin (Zocor).
What nutritional supplements are available to reduce cholesterol? - Artichoke is particularly helpful in relieving gastrointestinal problems that result from an inability to adequately process fats. Garlic assists the heart for centuries and has been used in herbal medicines for all manner of conditions.
What cholesterol lowering food are there? - Eating more fiber-rich foods may help to lower your blood cholesterol level. Soy products are also linked to reduced cholesterol because of their isoflavone content.