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. Most cholesterol is produced internally, not dietary in origin. It is present in higher concentrations in tissues which either produce more or have more densely packed membranes; for example the liver, spinal cord, brain and atheroma. Cholesterol plays a central role in many biochemical processes, but is best known for the association of cardiovascular disease with various lipoprotein cholesterol transport patterns in the blood.
Cholesterol is a waxy, fat-like substance found in every cell of the body. It is used to help digest fats, strengthen cell membranes and make hormones. Although cholesterol serves many important functions in the body, too much cholesterol in the blood can be dangerous. When blood cholesterol reaches high levels, it can build up on artery walls, increasing the risk of blood clots, heart attack and stroke. The bloodstream transports cholesterol throughout the body by special carriers called lipoproteins. The two major lipoproteins are low density lipoproteins (LDL) and high density lipoproteins (HDL). LDL is most often referred to as the "bad" cholesterol whereas HDL is knows the "good" cholesterol.
Cholesterol is excreted from the liver in bile and reabsorbed from the intestines. Under certain circumstances, when more concentrated, as in the the gallbladder, it crystallises and is the major constituent of most gallstones, although lecitin and bilirubin gallstones also occur less frequently. Cholesterol is minimally soluble in water; it cannot dissolve and travel in the water-based blood stream. Instead, it is transported in the blood stream by lipoproteins; protein 'molecular-suitcases' which are water soluble and carry cholesterol and fats internally. The proteins forming the surface of the given lipoprotein particle determine from what cells cholesterol will be removed and to where it will be supplied.
The largest lipoproteins, which primarily transport fats from the intestinal mucosa to the liver are called chylomicrons. They carry mostly triglyceride fats and cholesterol (both from food and especially internal cholesterol secreted by the liver into the bile). In the liver, chylomicron particles give up triglycerides and some cholesterol and are converted into low-density lipoprotein (LDL) particles which carry triglycerides and cholesterol on to other body cells. In healthy individuals the low-density lipoprotein (LDL) particles are large and relatively few in number. Conversely, large numbers of small low-density lipoprotein (LDL) particles are strongly associated with promoting atheromatous disease within the arteries. (Lack of information on low-density lipoprotein (LDL) particle number and size is one of the major problems of conventional lipid tests.)
High-density lipoprotein (HDL) particles transport cholesterol back to the liver for excretion, but vary considerably in their effectiveness for doing this. Having large numbers of large HDL particles correlates with better health outcomes. Conversely, having small amounts of large HDL particles is strongly associated with atheromatous disease progression within the arteries. (Note that the concentration of total HDL does not indicate the actual number of functional large HDL particles, one of the major problems of conventional lipid tests.) The cholesterol in LDL cholesterol and the cholesterol in HDL cholesterol are identical. The only difference between the two is the carrier protein molecules (i.e. the lipoprotein).
Cholesterol is an important component of the membranes of cells, providing stability. It is the major precursor for the synthesis of vitamin D, of the various steroid hormones, including cortisol, cortisone, and aldosterone in the adrenal glands, and of the sex hormones progesterone, estrogen, and testosterone. Further recent research shows that cholesterol has an important role for the brain synapses as well as in the immune system, including protecting against cancer.
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.