Cholesterol Levels


Blood tests are needed to determine how much of your cholesterol is carried by high-density lipoproteins (good) and low-density lipoproteins (bad).
Blood tests are needed to determine how much of your cholesterol is carried by high-density lipoproteins (good) and low-density lipoproteins (bad).
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Doctors test cholesterol levels to determine how much cholesterol is carried by low density cholesterol and how much is carried by HDL cholesterol. Determining these cholesterol levels can indicate whether more cholesterol is remaining in the bloodstream, which can lead to atherosclerosis, a condition in which plaque builds up in the arteries.

Blood helps to transport cholesterol through the body. Because cholesterol is a lipid, it doesn't mix with water. Blood, however, is made up of a substantial amount of water. Therefore, in order to move cholesterol through the bloodstream, the body wraps it in proteins, forming lipoproteins. The lipoproteins glide through the bloodstream like microscopic submarines carrying cargoes of cholesterol to destinations in the body.

Two types of lipoproteins that play a major role in transporting cholesterol are low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). LDLs are called the "bad" cholesterol, and HDLs are called the "good" cholesterol.

Two other types of lipoproteins include very low-density lipoproteins (VLDLs) and chylomicrons. VLDLs carry triglycerides (fat molecules) that are made in the liver, along with some cholesterol, to cells where the triglycerides can be stored. Depositing the triglycerides in the cells leaves mostly cholesterol, turning the VLDLs into plain old LDLs. Chylomicrons are responsible for picking up dietary cholesterol from the intestines after it has been absorbed from food.

The level of cholesterol in your blood is expressed in "milligrams per deciliter (mg/dL)," which indicates the weight of the cholesterol found in one deciliter of blood. Blood-cholesterol tests usually measure the total amount of cholesterol in your blood. Tests and calculations can also be performed to see how much of that cholesterol is contained in the form of LDLs and HDLs.

If cholesterol is normally present in your blood, why should you worry about it? The reason is that the total amount of cholesterol in your blood reveals how efficiently your body is using and managing cholesterol. Excessive cholesterol in your blood may mean that something is going wrong with how your body is using cholesterol.

­When more of the cholesterol in your blood is being carried by HDLs, the "good" cholesterol, there is less danger of cholesterol accumulating in the body. If LDLs, the "bad" cholesterol, are carrying more of the cholesterol, the balance is tipped in favor of cholesterol remaining in the body.

­­We'll start out by learning about the "bad" form of cholesterol. The next page explains LDL cholesterol.

LDL Cholesterol

LDLs deposit excess cholesterol in your arteries as plaque, clogging the arteries. This is similar to a pipe being clogged by rust and other materials.
LDLs deposit excess cholesterol in your arteries as plaque, clogging the arteries. This is similar to a pipe being clogged by rust and other materials.
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LDLs, called the "bad" cholesterol, carry cholesterol to the body's cells, where it can be stored, woven into the cell membranes, or used to make vitamin D or steroid hormones. LDL isn't "bad" because of this activity. However, it's considered "bad" when the body's cells don't accept the LDL, and it remains in the bloodstream.

Only certain types of cells accept cholesterol from LDLs. These cells have special structures called receptors located on the surface of their membranes that are responsible for pulling in the cholesterol from the LDLs. A large number of these receptors are found on the surface cells of the liver; the rest are found on a variety of other cells in the body.

When these cells have taken up all the cholesterol they can manage for use, the number of receptors shrinks to decrease the amount of cholesterol entering the cell. Any extra LDL cholesterol then remains in the blood. This is where the danger to your heart lies. The LDLs take the unused cholesterol and deposit it in the walls of your arteries as plaque, causing a condition known as coronary atherosclerosis.

A person who has a high total blood-cholesterol level usually has a high level of LDLs. Several studies have shown that a high level of LDLs is an independent risk factor for coronary heart disease. An independent risk factor is a trait, condition, or habit that is associated with an increased chance of developing a disease, regardless of whether other traits or conditions are present.

In one study, when scientists looked at the arteries of young people who had died from causes other than heart disease, they found that the victims who had high levels of LDL cholesterol also had more fatty buildup in their arteries.

Further evidence of the role of LDLs comes from studies of the Pima Indians. Although obesity and diabetes are common among the members of this group, they have low total cholesterol levels, low LDL-cholesterol levels, and low rates of coronary heart disease.

Studies of families with an inherited defect that causes high LDL levels also implicate LDLs as the key to coronary heart disease risk. In an informative study of 116 families with familial hypercholesterolemia (inherited high cholesterol) conducted by the National Institutes of Health, family members who had the defect not only had a higher risk of coronary heart disease than unaffected family members, but their coronary heart disease occurred an average of 20 years earlier.

Studies of both diet and drug therapy have shown that lowering LDL-cholesterol levels decreases the risk of coronary heart disease. If you want to lower your risk of coronary heart disease, lowering your level of LDLs is the place to start.

­Of course, LDLs aren't the only important kind of cholesterol. High levels of HDL cholesterol can lower the risk incurred by high levels of LDL cholesterol. Learn why on the next page.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

HDL Cholesterol

Getting regular physical activity is an easy lifestyle change you can make to increase your protective HDL cholesterol.
Getting regular physical activity is an easy lifestyle change you can make to increase your protective HDL cholesterol.
Publications International, Ltd.

 

HDLs, the "good" cholesterol, are thought to carry cholesterol from the cells back to the liver so it can be removed from the body in bile. HDL is also thought to act as an antioxidant, preventing harmful changes to LDL cholesterol that make it more likely to damage the walls of arteries.

Measurement of the level of your HDL cholesterol is a powerful tool in assessing your risk of coronary heart disease. The higher the level of HDL cholesterol, the better it is for your heart.

In the early 1950s, scientists realized that patients with coronary heart disease had low levels of HDLs. A study done in 1966 found that men with low levels of HDL-2, a cholesterol-rich portion of HDL, were more likely to develop coronary heart disease.

Beginning in 1968, as part of the Framingham Heart Study, 2,815 men and women aged 49 through 82 had both their lipoproteins and fasting lipids measured. The men and women who had low levels of HDL cholesterol (less than 35 mg/dL) had eight times the risk of coronary heart disease as did those who had HDL-cholesterol levels above 65 mg/dL.

A 12-year follow-up showed that the group that had HDL levels below 53 mg/dL experienced 60 to 70 percent more heart attacks than the group with higher HDL levels.

In addition, the researchers found that low HDLs could predict the risk of heart attack in people who had the lowest total cholesterol levels. Finally, those people with low HDL cholesterol showed the most improvement when given LDL-lowering drug therapy, such as statins. This is because lowering LDL cholesterol reduces the risk of coronary heart disease.

Research has shown that a low level of HDL cholesterol is an independent risk factor of coronary heart disease. Even if LDL-cholesterol levels are within normal range, if HDL-cholesterol levels are low, the risk of a coronary event is increased.

Studies have indicated that for every 1 percent increase in HDL, the risk of coronary heart disease decreases by 2 to 3 percent. This means that even small improvements in HDL-cholesterol levels can prove markedly beneficial.

Most people can modify their diet and lifestyle to improve their HDL-cholesterol levels. Quitting smoking and losing weight can significantly increase HDL-cholesterol levels. Regular physical activity, moderate alcohol consumption, lower intakes of carbohydrates, and a Mediterranean-style diet have also been linked with improving levels of HDL cholesterol.

Despite evidence up to now indicating that HDL cholesterol is beneficial, some researchers now believe that not all HDL cholesterol is good, and they are conducting studies to determine if some forms of HDL promote inflammation, a key process involved in the development of atherosclerosis. Results of these studies are eagerly awaited.

Research also focuses on the specific proteins that are in HDL and LDL cholesterol. Learn about these apolipoproteins on the next page.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Apolipoproteins

Doctors measure apolipoproteins for clues to the risk of coronary heart disease.
Doctors measure apolipoproteins for clues to the risk of coronary heart disease.
Publications International, Ltd.

You may hear about tests that measure apolipoproteins, which are the specific types of proteins that your HDLs and LDLs contain. They are alphabetically designated as A, B, C, D, and E.

LDL contains apolipoprotein B (apo B); HDL contains apolipoprotein A-1 (apo A1). A recent study indicated that, in comparison to the standard blood-cholesterol tests, the ratio of apo B to apo A1 is the best predictor of those at risk of heart attack. For example, some people who have normal levels of LDL may have higher-than-normal levels of apo B (usually there's only one apo B molecule on each LDL), and this higher level may indicate greater risk.

One clue to an increase in the number of apo B particles is an elevated level of triglycerides -- 150 mg/dL or greater. When LDL-cholesterol levels are normal but triglyceride levels are elevated, something called non-HDL cholesterol should be measured.

Non-HDL cholesterol is the total of VLDL and LDL cholesterol, both of which contain apo B particles. As a result, measurement of non-HDL cholesterol provides more accurate information about atherogenic particles.

Finally, a low level of apo A1, the apolipoprotein found on HDL, indicates a greater risk of coronary heart disease. Currently, there doesn't seem to be any clinical advantage to measuring these smaller particles of HDL cholesterol, as this information doesn't affect the course of treatment; in the future, however, if effective medications are developed that target HDL cholesterol, this may change.

Preliminary research also appears to indicate that genetic differences in apo E, a key protein in the metabolism of LDLs, may predict a person's risk for coronary heart disease. For example, people who have one form of apo E appear to have higher LDL levels and develop coronary heart disease earlier than those with other forms. On the other hand, those who have a different form of apo E may have some protection from heart disease.

Researchers have also found a way to measure lipoprotein (a), or Lp(a), a cholesterol-rich lipoprotein that is associated with a tendency toward clotting (thrombosis) and enhanced plaque formation. In some studies, high levels of Lp(a) seem to indicate an increased risk of coronary heart disease in men and women. Estrogen and ­niacin are among the few drugs that are known to lower Lp(a). However, because the research findings relating Lp(a) and coronary heart disease are not consistent, routine measurement and treatment of Lp(a) are not recommended. This measurement may, however, be helpful in individuals with a personal or family history of premature coronary heart disease, indicating additional benefit from a more intensive reduction in LDL cholesterol.

Measurements of apolipoproteins are providing researchers with more and more tools for predicting an individual's risk of coronary heart disease. Some of these tests are becoming available at laboratories. Talk with your doctor to determine if any of these newer tests, in addition to the standard blood-cholesterol tests, would be beneficial in providing more information about your cholesterol levels. Be advised, however, that not all these tests are standardized, they tend to be more expensive, and they may not provide information that would change the course of treatment.

Along with apolipoproteins and overall cholesterol, doctors must check your triglycerides. On the next page, learn what these are and why a high level of triglycerides may be harmful.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.

Triglycerides

Most fats in food are made up primarily of triglycerides. In order to use the energy stored in fat, the body breaks down triglycerides into fatty acids, which individual cells burn for energy. Like cholesterol, some fat is normally found in the blood; it travels through the bloodstream to get from its food sources and body stores to the cells that use it. Fat also needs lipoproteins to carry it through the bloodstream.

To illustrate how important these lipoproteins are for fat transport, drop a tablespoon of oil into a glass of water and watch what happens. The fat and water repel each other. This reaction makes transport of fat through blood difficult. When fat is encased in a lipoprotein that prevents it from mixing with blood, however, it can move effortlessly through the bloodstream.

Although all lipoproteins carry some triglycerides, chylomicrons (a lipoprotein) and the very-low-density lipoproteins (VLDLs) are the primary movers of triglycerides. Each transports triglycerides from a particular source.

When fat from foods is digested in the body, the fatty acids are released and then packaged into triglycerides in the intestines. The chylomicrons pick up these triglycerides, along with dietary cholesterol, and transport them through the blood to the muscle cells and fat cells. An enzyme residing on these cells breaks down the chylomicrons so that the fatty acids can enter the cells.

Cholesterol is left behind in the remnant, which makes its way to the liver. The enzyme works quickly: Within five minutes, it can clear from the blood half the triglycerides absorbed from a meal. Within a few hours after a meal the enzyme will have removed all the chylomicrons from the blood.

When your body makes its own fat in order to store extra calories from food, a different lipoprotein takes care of transportation. The VLDLs carry the fat that is made in the liver, along with cholesterol, to the cells where the fat is stored. Once the VLDLs have dropped off their triglycerides, they contain mostly cholesterol and evolve into LDL molecules.

Scientific research appears to show that the blood-triglyceride level, unlike blood-cholesterol level, does not independently predict risk of heart disease in the general population, although it did have predictive value for older women in the Framingham Heart Study. Doctors do not find large amounts of triglycerides in the plaques that clog arteries.

On the other hand, people who have survived heart attacks often do have high blood-triglyceride levels. A high triglyceride level may be one indicator of something called the metabolic syndrome, which is also characterized by abdominal obesity, low levels of HDL cholesterol, high blood pressure, and insulin resistance. People with metabolic syndrome are at an increased risk of coronary heart disease.

Cholesterol is a delicate balancing act. With the newfound knowledge from this article, you'll be better equipped to control your own cholesterol.

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ABOUT THE AUTHOR

Dr. Neil Stone is a professor of clinical medicine in cardiology at the Feinberg School of Medicine of Northwestern University and a practicing internist-cardiologist-lipidologist at Northwestern Memorial Hospital. He also serves as the Medical Director of the Vascular Center for the Bluhm Cardiovascular Institute. Dr. Stone was a member of the first and third National Cholesterol Education Program Adult Treatment Panels and a past chairman of the American Heart Association Nutrition Committee and Clinical Affairs Committee.