What is cholesterol?
Cholesterol is a fatty substance (a lipid) that is an important part of the outer lining (membrane) of cells in the body of animals. Cholesterol is also found in the blood circulation of humans. The cholesterol in a person's blood originates from two major sources; dietary intake and liver production. 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, cholesterol is absorbed by the intestines into the blood circulation and is then packaged inside a protein coat. This cholesterol-protein coat complex is called a chylomicron.
The liver is capable of removing cholesterol from the blood circulation as well as manufacturing cholesterol and secreting cholesterol into the blood circulation. After a meal, the liver removes chylomicrons from the blood circulation. In between meals, the liver manufactures and secretes cholesterol back into the blood circulation.
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.
Does lowering LDL cholesterol prevent heart attacks and strokes?
Lowering LDL cholesterol is currently the primary focus in preventing atherosclerosis and heart attacks. Most doctors now believe that 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;
* Widening narrowed arteries;
* Preventing the rupture of cholesterol plaques, which initiates blood clot formation;
* Decreasing the risk of heart attacks; and
* Decreasing the risk of strokes. The same measures that retard atherosclerosis in coronary arteries also benefit the carotid and cerebral arteries (arteries that deliver blood to the brain).
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 in both men and 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 are lower in persons who smoke cigarettes, eat a lot of sweets, are overweight and inactive, and in patients 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>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 nicotinic acid (niacin), 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, chylomicrons, 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. Thus, after a meal, the triglyceride and cholesterol that are absorbed into the intestines are packaged into round particles called chylomicrons before they are released into the blood circulation.
A chylomicron is a collection of cholesterol and triglyceride that is surrounded by a lipoprotein outer coat. (Chylomicrons contain 90% triglyceride and 10% cholesterol.)
The liver removes triglyceride and chylomicrons from the blood, and it synthesizes and packages triglyceride into VLDL (very low-density lipoprotein) particles and releases them back into the blood circulation.
Cholesterol is a fatty substance (a lipid) that is an important part of the outer lining (membrane) of cells in the body of animals. Cholesterol is also found in the blood circulation of humans. The cholesterol in a person's blood originates from two major sources; dietary intake and liver production. 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, cholesterol is absorbed by the intestines into the blood circulation and is then packaged inside a protein coat. This cholesterol-protein coat complex is called a chylomicron.
The liver is capable of removing cholesterol from the blood circulation as well as manufacturing cholesterol and secreting cholesterol into the blood circulation. After a meal, the liver removes chylomicrons from the blood circulation. In between meals, the liver manufactures and secretes cholesterol back into the blood circulation.
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.
Does lowering LDL cholesterol prevent heart attacks and strokes?
Lowering LDL cholesterol is currently the primary focus in preventing atherosclerosis and heart attacks. Most doctors now believe that 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;
* Widening narrowed arteries;
* Preventing the rupture of cholesterol plaques, which initiates blood clot formation;
* Decreasing the risk of heart attacks; and
* Decreasing the risk of strokes. The same measures that retard atherosclerosis in coronary arteries also benefit the carotid and cerebral arteries (arteries that deliver blood to the brain).
The 2004 NCEP treatment goals according to risk categories
| Risk category | LDL goal | More intense LDL goal option | Initiate TLC if LDL is: | Consider drugs + TLC if LDL is: |
| High risk | <> | | > 100 mg/dl | >100 mg/dl |
| Very high risk | <> | <> | > 100 mg/dl | <100> |
| Moderately high risk (10 yr. risk 10-20%) | <130> | <100> | > 130 mg/dl | >130mg/dl, consider drug option if LDL is 100-129 mg/dl |
| Moderate risk (10 yr. risk <10%) | <130> | | > 130 mg/dl | >160 mg/dl |
| Lower risk | <160> | | > 160 mg/dl | >190 mg/dl, consider drug optional if LDL is 160-189 mg/dl |
- High risk patients are those who already have coronary heart disease (such as a prior heart attack), diabetes mellitus, abdominal aortic aneurysm, or those who already have atherosclerosis of the arteries to the brain and extremities (such as patients with strokes, TIA's (mini-strokes), and peripheral vascular diseases). High risk patients also include those with 2 or more risk factors (e.g., smoking, hypertension, or a family history of early heart attacks) that places them at a greater than 20 percent chance of having a heart attack within 10 years. (A person's chance of having a heart attack can be calculated by using the Framingham Heart Study Score Sheets, at http://nhlbi.nih.gov/about/framingham/riskabs.htm).
- Very high -risk patients are those who have coronary heart disease in addition to having either multiple risk factors (especially diabetes), or severe and poorly controlled risk factors (such as continued smoking), or metabolic syndrome (a constellation of risk factors associated with obesity, including high triglycerides and low HDL). Patients hospitalized for acute coronary syndromes are also at very high risk.
- Moderately high risk patients are those who have neither coronary heart disease nor diabetes mellitus, but have multiple (2 or more) risk factors for coronary heart disease that put them at a 10 to 20 percent risk of heart attack within 10 years. (Use the Framingham Heart Study Score Sheets, at http://nhlbi.nih.gov/about/framingham/riskabs,htm to calculate the 10 year risk.)
- Moderate risk patients are those who have neither CHD nor diabetes mellitus, but have 2 or more risk factors for coronary heart disease that put them at a <10%>
- Lower risk patients are those with 0 to 1 risk factor for coronary heart disease.
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 in both men and 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 are lower in persons who smoke cigarettes, eat a lot of sweets, are overweight and inactive, and in patients 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>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 nicotinic acid (niacin), 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, chylomicrons, 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. Thus, after a meal, the triglyceride and cholesterol that are absorbed into the intestines are packaged into round particles called chylomicrons before they are released into the blood circulation.
A chylomicron is a collection of cholesterol and triglyceride that is surrounded by a lipoprotein outer coat. (Chylomicrons contain 90% triglyceride and 10% cholesterol.)
The liver removes triglyceride and chylomicrons from the blood, and it synthesizes and packages triglyceride into VLDL (very low-density lipoprotein) particles and releases them back into the blood circulation.
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