Understanding Cholesterol

Most Americans are familiar with the term cholesterol but may not be fully acquainted with how it applies to heart and vascular (blood vessel) health. Understanding how cholesterol levels are measured and what the values mean can provide a basis for making healthy lifestyle choices and preventing the complications of cardiovascular disease (CVD). This is an overview of the different types of cholesterol and how a fasting lipid panel, or cholesterol test, can help to determine a person’s risk for CVD.

CVD is the number one killer in the United States. The term CVD encompasses a number of specific diseases such as heart disease, stroke, and peripheral vascular disease (PVD). All of these conditions share a common connection in that they are caused by damage to the blood vessels and the build-up of plaque, cholesterol deposits, in the arteries. In 2005, heart disease alone accounted for over 600,000 deaths in the United States according to the Centers for Disease Control.

Cholesterol is actually a very important compound that is necessary for the proper functioning of cells in the human body. Cholesterol is one of the major components of the membrane (think of it like the cell’s skin, which keeps the good things in the bad things out) of all cells in the body and is also used to make a variety of hormones such as testosterone and estrogen. Cholesterol is obtained through the diet and is also produced by the body from other compounds.

THE LIPID PANEL (“CHOLESTEROL TEST”)

When a patient has blood work drawn to “measure cholesterol,” what is really being measured are the levels of several different complex molecules involved in the regulation of cholesterol levels in the body. These molecules are referred to as lipoproteins. This is why the technical term for a cholesterol test is a lipid panel or lipid profile. Lipoproteins are a combination of proteins, lipids (fats), and cholesterol. The concentration of certain lipoproteins in the blood has a direct correlation with cardiovascular health and disease.

Standard lipid panels report the following compounds: Total Cholesterol, LDL, HDL, and triglycerides. The concentration of each of these compounds is reported as milligrams of lipid per deciliter of blood (mg/dL). Each of these four substances has been found, through extensive research, to predict an individual’s risk for developing CVD. Modulation, through diet and exercise, of any of all of these can greatly reduce an individual’s risk of death or disability from CVD.

LDL is often referred to as the “bad cholesterol” because increases in LDL are directly related to increases in the risk of CVD. When a person ingests cholesterol, it is loaded onto special molecules called chylomicrons that help move it from the intestine to the blood stream. Once in the blood stream, LDL carries cholesterol to the locations that need it. If an individual has an overabundance of cholesterol, either from diet or from increased production, the LDL level in the blood will increase. When the level of LDL in the blood exceeds the needs of the body for cholesterol, the excess is deposited in epithelial tissue because the LDL has nowhere else to put it does not have the ability to remove the cholesterol from the body. Epithelial tissue makes up the lining of arteries and veins. When epithelial cells start to accumulate cholesterol, plaques begin to form. Plaques lead to narrowing of arteries, which reduces the flow of blood to tissues that need it. Reduced blood flow can lead to chest pain, heart failure, leg pain, stroke, and a variety of other conditions. The plaques can also rupture because they are unstable and are subjected to a lot of wear and tear from the constant movement of blood within the arteries. When a plaque ruptures, the pieces can become clogged in arteries and obstruct blood flow. When this happens in the heart, a heart attack occurs. When this happens in the brain, it leads to stroke.

Lowering LDL cholesterol is one of the primary goals of lipid management and the most important factor in reducing the risk of CVD. LDL is considered borderline high at 130 mg/dL, high at 160 mg/dL and very high at 190 mg/dL. The optimal LDL level, depending on other diseases a person may have, is less than 100 mg/dL.

HDL is often referred to as the “good cholesterol.” It earned this name because it has the opposite features of LDL. HDL is like a scavenger; it travels around in the blood looking for “extra” cholesterol which it then picks up and takes back to the liver. Once in the liver, the cholesterol is excreted from the body in the form of bile. A person’s risk of CVD is inversely related to his or her HDL level. As HDL increases, the risk of CVD decreases. HDL levels are considered too low if they are less than 40 mg/dL in men or less than 50 mg/dL in women.

Total cholesterol represents a combination of LDL, VLDL, IDL (intermediate density lipoprotein), and HDL cholesterols. VLDL and IDL are not directly useful in calculating CVD risk and so are not included in a lipid screen as individual entities. They are, however, included in the measurement of total cholesterol. Current recommendations for total cholesterol suggest a level of 200 mg/dL or less is optimal. A level of 240 mg/dL is considered high and requires treatment.

Total cholesterol alone does not correlate with CVD as well as LDL and HDL cholesterol. However, the ratio of total cholesterol to HDL (calculated by dividing the total cholesterol concentration by the HDL concentration) is highly predictive of risk of CVD. This makes intuitive sense given that HDL is the “good cholesterol” and LDL the “bad cholesterol.” The higher the HDL or the lower the total cholesterol, the lower the ratio will be of total cholesterol to HDL. In women, a ratio of 5.6 or greater is associated with an increased risk of CVD. In men, a ration of 6.4 or greater is associated with an increased risk of CVD. The increased total cholesterol to HDL ratios above confer a risk of CVD that is over and above what would be predicted on the basis of LDL cholesterol alone, suggesting that the effects of low HLD and high LDL in these patients are synergistic and not simply additive. These individuals are candidates for more aggressive cholesterol lowering therapy than those who do not demonstrate an increased total cholesterol to HDL ratio.

Triglycerides, the final component of the lipid panel, are simply fats. An elevated triglyceride level is directly associated with an increased risk of CVD. Triglycerides can also contribute to the development of plaques in the arteries, but are more importantly linked to obesity, high blood pressure, and diabetes. All of these conditions greatly increase the risk of CVD. Triglyceride levels should ideally be less than 150 mg/dL and are considered high when greater than 200 mg/dL. Levels greater than 500 mg/dL are extremely dangerous and require aggressive medical therapy.

Cholesterol management is generally targeted at lowering LDL and triglyceride levels because available medications are better suited to lowering these values than to raising HDL levels. Diet and lifestyle modifications are more important in the management of HDL than drugs at the moment. As biomedical research progresses, however, there are likely to be more drugs targeted specifically at raising HDL levels. Efforts are made to increase HDL levels only when they drop below 40 mg/dL in men and 50 mg/dL in women. Some studies suggest that the affects of HDL levels are more important for women than men, suggesting that raising HDL levels should be a more prominent management criterion in women.

The ultimate goals set for levels of LDL, HDL, and triglycerides are different for each individual. While the numbers above offer rough guidelines for treatment, therapy must ultimately be tailored to fit the individual needs and comorbid diseases of specific patients. In patients with coronary artery disease equivalents, such as known coronary artery disease, previous heart attack, symptomatic carotid artery disease, an abdominal aortic aneurysm, peripheral artery disease (PAD), or diabetes, aggressive measures should be undertaken in order to decrease LDL levels below 100 mg/dL. Some cardiologists (heart doctors) would even recommend reducing LDL below 70 mg/dL in this population.

ADDITIONAL TESTING OPTIONS

Triglycerides, LDL, HDL, and total cholesterol are the measurements that appear on a standard lipid panel, but they are not the only lipids that can be measured in order to assess risk for CVD. Advanced testing can be done to further identify patients at risk of CVD. One of these other parameters is lipoprotein (a), abbreviated Lp (a). Lp (a) is a modified form of LDL to which apolipoprotein (a) has been attached. Lp (a) levels appear to be most important in assessing risk in those patients with elevated cholesterol levels who also have low HDL cholesterol. In these patients, elevated levels of Lp (a) are an independent risk factor for CVD, especially Coronary Heart Disease (CHD). A normal level of Lp (a) is less than 14 mg/dL. Patients are at high risk at levels over 30 mg/dL.

Other tests that may be undertaken include measurements of the size of LDL particles and measurement of non-HDL cholesterol. The size of LDL particles has been found to correlate with CVD in certain individuals. These are specialized tests that should only be order and interpreted by specialists.

THE BOTTOM LINE ON LIPID PANELS:

LDL is the most important measurement. LDL < 130 mg/dL is good, but LDL < 100 mg/dL is best. If the patient has a coronary artery disease equivalent then an LDL < 100 mg/dL is essential.

HDL ≥ 40 mg/dL in men or 50 mg/dL in women. HDL ≥ 60 mg/dL is great

Triglyceride < 150 mg/dL

Total cholesterol < 200 mg/dL

Lp (a) > 30 mg/dL is high risk. Lp (a) < 14 mg/dL is ideal.

Call HealthwoRx™ at 954.967.6550 to schedule an appointment with a doctor regarding your Cholesterol.

REFERENCES

Glew RH. Chapter 17: Lipid Metabolism II: Pathways of Metabolism of Special Lipids. In: Devlin TM. Textbook of Biochemistry with Clinical Correlations 5th edition. Wiley-Liss: New York 2002. P. 741-52.

Rosenson RS. Screening guidelines for dyslipidemia. On: UpToDate Online version 17.2. Updated Jan 22, 2009. Accessed Aug 19, 2009. uptodate.com/online/content/topic.do?topicKey=lipiddis/2059&selectedTitle=3~150&source=search_result#9

Rosenson RS. Measurement of serum lipoproteins. On: UpToDate Online version 17.2. Updated Apr 29, 2009. Accessed Aug 19, 2009. uptodate.com/online/content/topic.do?topicKey=lipiddis/4686&selectedTitle=13~150&source=search_result#6

Heart Disease. Heart Disease Facts and Statistics. CDC: Centers for Disease Control and Prevention. Updated Feb 12, 2009. Accessed Aug 19, 2009. cdc.gov/heartdisease/statistics.htm