what type of cholesterol is bad , and what type of cholesterol is good
Cholesterol Levels facts
•High cholesterol is also referred to as hypercholesterolemia (hyper=high + cholesterol + emia = in the blood) or hyperlipidemia
•Cholesterol is a fatty substance that is an important part of the outer lining of cells in the body of animals.
•Cholesterol is also found in the blood circulation of humans.
•Cholesterol in the blood originates from dietary intake and liver production.
•Dietary cholesterol comes primarily from animal sources including meat, poultry, fish, and dairy products.
•Organ meats such as liver, are especially high in cholesterol content.
•LDL (low density lipoprotein) cholesterol is called "bad" cholesterol, because elevated levels of LDL cholesterol are associated with an increased risk of coronary heart disease.
•HDL (high density lipoprotein) cholesterol is called the "good cholesterol" because HDL cholesterol particles prevent atherosclerosis by extracting cholesterol from artery walls and disposing of them through liver metabolism.
•High levels of LDL cholesterol and low levels of HDL cholesterol are risk factors for atherosclerosis.
•Research has shown that lowering LDL cholesterol reduces the risk of heart attacks, strokes, and peripheral artery disease.
•The National Institute of Health, the American Heart Association and the American College of Cardiology publish guidelines to help physicians and patients with this risk reduction for heart attack and stroke.
•Factors that affect blood cholesterol levels include diet, body weight, exercise, age and gender, diabetes, heredity, and other causes including underlying medical conditions.
•Guidelines recommend that cholesterol screening occur every 5 years after age 20. Should elevated cholesterol levels be found, testing may need to occur more frequently.
•Health care practitioners and the National Institute of Health recommend that a person's cholesterol level stay below 200.
•Cholesterol levels 200-239 are considered borderline high.
•Cholesterol levels 240 or greater are considered high.
•Drugs available to treat high cholesterol include statins, bile acid resins, and fibric acid derivatives.
•Drugs to lower blood cholesterol levels are most effective when combined with a low cholesterol diet.
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, stroke, and peripheral artery disease. LDL lipoprotein deposits cholesterol along the inside of 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, which decreases blood flow through the narrowed area.
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 levels of HDL cholesterol (low LDL/HDL ratios) are desirable and protect against heart disease and stroke.
Total cholesterol is the sum of LDL (low density) cholesterol, HDL (high density) cholesterol, VLDL (very low density) cholesterol, and IDL (intermediate density) cholesterol.
Why is HDL the good cholesterol?
HDL is the good cholesterol because it protects the arteries from the atherosclerosis process. HDL cholesterol extracts cholesterol particles from the artery walls and transports them to the liver to be disposed through the bile. It also interferes with the accumulation of LDL cholesterol particles in the artery walls.
The risk of atherosclerosis and heart attacks is strongly related to HDL cholesterol levels. Low levels of HDL cholesterol are linked to a higher risk, whereas high HDL cholesterol levels are associated with a lower risk.
Very low and very high HDL cholesterol levels can run in families. Families with low HDL cholesterol levels have a higher incidence of heart attacks than the general population, while families with high HDL cholesterol levels tend to live longer with a lower frequency of heart attacks.
Like LDL cholesterol, life style factors and other conditions influence HDL cholesterol levels. HDL cholesterol levels tend to be lower in persons who smoke cigarettes, are overweight and inactive, and in people with type II diabetes mellitus.
HDL cholesterol is higher in people who are lean, exercise regularly, and do not smoke cigarettes. Estrogen increases a person's HDL cholesterol, which explains why women generally have higher HDL levels than men do.
For individuals with low HDL cholesterol levels, a high total or LDL cholesterol blood level further increases the incidence of atherosclerosis and heart attacks. Therefore, the combination of high levels of total and LDL cholesterol with low levels of HDL cholesterol is undesirable whereas the combination of low levels of total and LDL cholesterol and high levels of HDL cholesterol is favorable.
What are LDL/HDL and total/HDL ratios?
The total cholesterol to HDL cholesterol ratio (total chol/HDL) is a number that is helpful in estimating the risk of developing atherosclerosis. The number is obtained by dividing total cholesterol by HDL cholesterol. (High ratios indicate a higher risk of heart attacks, whereas low ratios indicate a lower risk).
High total cholesterol and low HDL cholesterol increases the ratio and is undesirable. Conversely, high HDL cholesterol and low total cholesterol lowers the ratio and is desirable. An average ratio would be about 4.5. Ideally, one should strive for ratios of 2 or 3 (less than 4).
What are the treatment guidelines for low HDL cholesterol?
In clinical trials involving lowering LDL cholesterol, scientists also studied the effect of HDL cholesterol on atherosclerosis and heart attack rates. They found that even small increases in HDL cholesterol could reduce the frequency of heart attacks. For each 1 mg/dl increase in HDL cholesterol, there is a 2% to 4% reduction in the risk of coronary heart disease. Although there are no formal NCEP (please see discussion above) target treatment levels of HDL cholesterol, an HDL level of <40 mg/dl is considered undesirable and measures should be taken to increase it.
How can levels of HDL cholesterol be raised?
The first step in increasing HDL cholesterol levels (and decreasing LDL/HDL ratios) is therapeutic life style changes. When these modifications are insufficient, medications are used. In prescribing medications or medication combinations, doctors have to take into account medication side effects as well as the presence or absence of other abnormalities in cholesterol profiles.
Regular aerobic exercise, loss of excess weight (fat), and cessation of smoking cigarettes will increase HDL cholesterol levels. Regular alcohol consumption (such as one drink a day) will also raise HDL cholesterol. Because of other adverse health consequences of excessive alcohol consumption, alcohol is not recommended as a standard treatment for low HDL cholesterol.
Medications that are effective in increasing HDL cholesterol include gemfibrozil (Lopid), estrogen, and to a much lesser extent, the statin drugs (discussed below). A newer medicine, fenofibrate (Tricor) has shown much promise in selectively increasing HDL levels and reducing serum triglycerides.
What are triglycerides and VLDL?
Triglyceride is a fatty substance that is composed of three fatty acids. Like cholesterol, triglyceride in the blood either comes from the diet or the liver. Also, like cholesterol, triglyceride cannot dissolve and circulate in the blood without combining with a lipoprotein.
The liver removes triglyceride from the blood, and it synthesizes and packages triglyceride into VLDL (very low-density lipoprotein) particles and releases them back into the blood circulation.
What medications are available to lower cholesterol, lipids, and triglycerides?
Lipid altering medications are used in lowering blood levels of undesirable lipids such as LDL cholesterol and triglycerides and increasing blood levels of desirable lipids such as HDL cholesterol. Several classes of medications are available in the United States, including HMG CoA reductase inhibitors (statins), nicotinic acid, fibric acid derivatives, and medications that decrease intestinal cholesterol absorption (bile acid sequestrants and cholesterol absorption inhibitors). Some of these medications are primarily useful in lowering LDL cholesterol, others in lowering triglycerides, and some in elevating HDL cholesterol. Medications also can be combined to more aggressively lower LDL, as well as in lowering LDL and increasing HDL at the same time.
Note: Dosing guidelines change. The US Food and Drug Administration (FDA) issued a guideline concerning the potential dangers of taking the 80mg dose of simvastatin (Zocor).
Is lowering LDL cholesterol enough?
LDL cholesterol reduction is only part of the battle against atherosclerosis. Individuals who have normal or only mildly elevated LDL cholesterol levels can still develop atherosclerosis and heart attacks even in the absence of other risk factors such as cigarette smoking, high blood pressure, and diabetes mellitus. It is clear that while lowering LDL cholesterol below NCEP target levels is an important step, there are other factors involved in heart disease that are yet to be discovered.
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