Hypercholesterolemia is the medical term for high blood cholesterol levels. It is not a disease as such but a condition that raises a person's risk of coronary heart disease, stroke, and other disorders of the circulatory system.
Cholesterol is a waxy or fatty substance that the human body produces normally. About 75 percent of the cholesterol in the body is made by the liver and other cells; the remaining 25 percent comes from food. A certain amount of cholesterol is necessary to maintain the function of cell membranes; thus cholesterol is present in the walls of all body cells, including those in the skin, muscle tissue, nervous system, digestive tract, and other parts of the body.
The body also needs cholesterol to make bile (a substance produced in the liver that helps to digest fat), hormones, and vitamin D. This cholesterol is carried in the bloodstream attached to protein molecules. These combinations of cholesterol and protein molecules are called lipo-proteins. If more cholesterol is made than is needed for the body's functions, the waxy cholesterol may form deposits on the inner walls of arteries known as plaques.
Fatty plaque deposits are particularly likely to build up in the arteries that supply the heart with blood. These blood vessels are known as the
coronary arteries. Plaque deposits can become thick enough to partially block the coronary arteries. If the deposits remain in place, they eventually cause the arteries to stiffen or harden—a condition known as atherosclerosis. If the arteries become too narrow because of the plaques, they cannot carry enough blood to the heart to meet the needs of the heart muscle for oxygen. The oxygen-starved muscle may then produce a kind of chest pain known as angina. The fatty plaques can also come loose from the walls of the artery, resulting in the formation of a clot, acompleteblockageofthe coronary artery,and a heart attack.
It is important to understand that there are three different types of cholesterol and lipoproteins in the human body:
- Low-density lipoprotein (LDL). Often called “bad” cholesterol, LDL is the type of cholesterol that forms plaques on the walls of the coronary arteries.
- High-density lipoprotein (HDL). The “good” cholesterol, HDL picks up LDL and takes it back to the liver. Between 25 and 32 percent of the body's cholesterol is HDL.
- Very low-density lipoprotein (VLDL). This type of cholesterol contains the highest levels of triglycerides (a type of fat) attached to its protein molecules. VLDL is converted in the bloodstream to LDL and can increase the size of LDL particles, thus speeding up the formation of plaques and atherosclerosis.
High blood cholesterol levels are largely an adult health problem. Women in the United States before menopause usually have lower blood cholesterol levels than men of the same age. As women and men age, however, their blood cholesterol levels rise until about sixty to sixty-five years of age. After about age fifty, women often have higher total cholesterol levels than men of the same age.
Race and ethnicity appear to affect the rates of hypercholesterolemia in the United States. According to a government health survey carried out
in the 1990s, Caucasian adults are more likely (19 percent) to have high blood cholesterol levels than Hispanics (15 percent) or African Americans (16 percent).
Other risk factors for high blood cholesterol include:
- Smoking. Smoking damages the walls of the coronary arteries, making it easier for plaques to form. It also lowers the level of HDL cholesterol.
- A high-fat diet. Such high-fat foods as red meat, eggs, and full-fat milk and cheese raise blood cholesterol levels.
- Lack of exercise. Exercise helps to raise HDL levels and lower LDL levels.
- High blood pressure. Like smoking, high blood pressure damages the walls of the coronary arteries.
- Diabetes. High levels of blood sugar raise LDL levels and lower HDL levels.
- Family history of heart disease. A parent or sibling who developed heart disease before age fifty-five places a person with high cholesterol levels at a greater than average risk of developing heart disease.
- Emotional stress. Several studies have shown that high stress levels for long periods of time raise blood cholesterol levels.
The basic cause of high blood cholesterol levels is a combination of genetic factors and lifestyle factors, particularly diet. There is one specific form of hypercholesterolemia called familial hypercholesterolemia that affects about one person in every 500 in the United States. Familial hypercholesterolemia is caused by a mutation in one specific gene known as the LDLR gene.
Genetic factors, however, also affect other people's risk of hypercholesterolemia. As of 2008 no other specific genes had been associated with high blood cholesterol levels in the general population; researchers think that there are probably several such genes rather than only one. These genetic factors contribute to high cholesterol levels either by interfering with the body's ability to remove LDL cholesterol from the bloodstream or by allowing the liver to produce too much cholesterol.
A person can have high blood cholesterol levels without any noticeable symptoms. Because of this fact, the National Cholesterol Education Program (NCEP) guidelines suggest that everyone aged twenty years and older should have their blood cholesterol level measured at least once every five years.
Blood cholesterol levels are measured by a blood test taken early in the morning after nine to twelve hours of fasting. The doctor will ask the patient about a family history of high cholesterol or heart disease as well as drawing the blood, since high cholesterol levels can be hereditary.
The blood cholesterol test measures total blood cholesterol, LDL, HDL, and triglyceride levels using units called milligrams per deciliter (mg/dL).
- Total cholesterol: Less than 200 mg/dL is a desirable level that lowers a person's risk for heart disease. A cholesterol level of 200 mg/dL or greater increases the risk. A level of 240 mg/dL and above is considered high blood cholesterol. The risk of heart disease at this level is twice that of a person whose total cholesterol level is 200 mg/dL.
- LDL: Less than 100 mg/dL is considered the best level; a level of 100–129 mg/dL is good; a level of 130–159 mg/dL is borderline high; a level of 160–189 mg/dL is high; and a level of 190 mg/dL and above is very high.
- HDL: A level below 40 mg/dL is considered a major risk factor for heart disease; a level between 40 and 59 mg/dL is better; and a level above 60 mg/dL is considered protective against heart disease.
- Triglycerides: Less than 150 mg/dL is normal; a level of 150–199 mg/dL is borderline high; a level of 200–499 mg/dL is high; and a level of 500 mg/dL or above is very high.
Treatment for hypercholesterolemia begins with lifestyle changes, including following strict dietary guidelines and increasing one'samount of daily exercise. There is some evidence that a vegetarian diet is beneficial.
In addition to lifestyle changes, the patient'sdoctormay recommend one or more medications to lower LDL and/or triglyceride levels.
The most common types of drugs used to control hypercholesterolemia are:
- Statins. These are drugs that block the liver from using a substance it needs to make cholesterol. As the level of cholesterol in the liver drops, the liver begins to remove excess cholesterol from the bloodstream.
- Bile acid-binding resins. These are drugs that work by prompting the liver to make more bile acid; to do this, the liver needs to draw cholesterol from the blood.
- Cholesterol absorption inhibitors. These medications work by limiting the amount of cholesterol that the small intestine can absorb from food.
- Fibrates. These are drugs that speed up the removal of triglycerides from the bloodstream.
- Niaspan. Niaspan is a prescription form of niacin (a B vitamin) that works by limiting the liver's ability to produce VLDL and LDL cholesterol.
The prognosis of hypercholesterolemia depends on the person's age, sex, family history, and willingness to follow a treatment program. The statins in particular have greatly improved a person's ability to lower his or her risk of coronary heart disease. The United States Preventive Services Task Force (USPSTF) has estimated that five to seven years of treatment with statins can lower the risk of heart disease by 30 percent.
People cannot change their age, sex, genetic factors, or family history that may increase their risk of high cholesterol levels, but they can manage their risk by getting plenty of exercise, keeping their weight at a healthy level, quitting smoking, and eating foods that help to lower LDL levels.
Specific dietary recommendations include:
- Eating foods that are low in saturated fats.
- Keeping cholesterol intake from foods below 200 milligrams per day. One egg, for example, contains about 210 milligrams of cholesterol. Eating lean meats, drinking skim instead of whole milk, and using egg substitutes are good ways to lower one's intake of cholesterol from foods.
- Eating whole-grain breads.
- Adding more servings of fruits and vegetables to the diet. These foods are rich in fiber, which can lower blood cholesterol levels.
- Eating more fish. Some types of fish, such as cod, halibut, and tuna, are lower in fat and cholesterol than poultry or red meat.
- Keeping one's alcohol intake moderate.
Researchers are presently focusing on the genetic factors involved in hypercholesterolemia as well as potential new treatments for it. As of 2008, the National Institutes of Health (NIH) was conducting almost 400 separate studies on high blood cholesterol, ranging from clinical trials of new statins to studies of statins in combination with other drugs, and several experimental drugs.
SEE ALSO Coronary artery disease; Heart attack; Stroke
WORDS TO KNOW
Angina: Chest pain caused by inadequate supply of oxygen to the heart muscles.
Atherosclerosis: Stiffening or hardening of the arteries caused by the formation of plaques within the arteries.
Cholesterol: A fatty substance produced naturally by the body that is found in the membranes of all body cells and is carried by the blood.
Plaque: A deposit of cholesterol along the inside wall of an artery.
Triglyceride: A type of fat made in the body.
American Heart Association. To Your Health! A Guide to Heart-Smart Living. New York: Clarkson Potter, 2001.
Durstine, J. Larry. Action Plan for High Cholesterol. Champaign, IL: Human Kinetics, 2006.
American Academy of Family Physicians (AAFP). Cholesterol: What Your Level Means. Available online at http://familydoctor.org/online/famdocen/home/common/heartdisease/risk/029.html (updated October 2007; accessed on August 4, 2008).
American Heart Association (AHA). About Cholesterol. Available online at http://www.americanheart.org/presenter.jhtml?identifier=512 (updated April 3, 2008; accessed on August 4, 2009).
National Heart, Lung, and Blood Institute (NHLBI). High Blood Cholesterol. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/Hbc/HBC_WhatIs.html (updated February 2006; accessed on August 4, 2008).