Cholesterol, is a fatty substance found in animal tissues. The
human body produces cholesterol, but this substance also enters the body in food. Meats,
egg yolks, and milk products, such as butter and cheese, contain cholesterol. Such organs
as the brain and liver contain much cholesterol.
Cholesterol is a type of lipid, one of the classes of chemical
compounds essential to human health . Cholesterol makes up an important part of the
membranes of each cell in the body. In addition, the liver uses cholesterol to make bile
acids, which aid digestion. The body also uses cholesterol to produce vitamin D and
certain hormones, including sex hormones.
Cholesterol and triglycerides, another lipid, are two of the major
fatty substances in the blood . Triglycerides may be used by cells for energy, or they may
be stored for later use. Doctors often measure the amount of cholesterol and triglycerides
in blood to help determine a patient's overall health. High levels of cholesterol,
particularly if accompanied by high levels of triglycerides, increase the risk of heart
Both cholesterol and triglycerides are carried through the bloodstream
in large molecules called lipoproteins. There are two chief types of cholesterol-carrying
lipoproteins, low-density lipoprotein (LDL) and high-density lipoprotein (HDL).
Cholesterol in blood can thus be identified as either LDL-cholesterol or HDL-cholesterol,
depending on which lipoprotein carries it. High levels of LDL-cholesterol in blood are a
primary cause of heart attacks. LDL can be found in the wall of heart arteries. Low levels
of HDL-cholesterol also increase the risk of heart attack. Some scientists believe that
HDLs help remove cholesterol from tissues.
Factors that cause high cholesterol levels. The amount of cholesterol
in the human body is controlled by cellular molecules that are called LDL-receptors. These
molecules allow LDL-cholesterol to attach to and be used by the cell. LDL-cholesterol
accumulates in blood in large amounts when the LDL-cholesterol in the body far exceeds the
number of available LDL-receptors. This condition most commonly occurs in people whose
diets are high in cholesterol or in saturated fats. Saturated fats are found primarily in
animal fats and in certain vegetable fats, such as coconut oil and palm oil.
People also may have high cholesterol levels if they have an abnormal
gene that prevents a full number of LDL-receptors from forming. This inherited disorder is
called familial hypercholesterolemia. Other factors that can cause high blood cholesterol
include a malfunctioning thyroid gland, kidney disease, diabetes, and the use of various
medicines, including certain diuretics.
Cholesterol and heart disease
In adults, a cholesterol level of less than 200 milligrams
per 1 deciliter (3 ounces) of blood is considered desirable. Above that level, the risk of
heart disease increases dramatically. Adults also are at an above-average risk of heart
disease if they have an LDL-cholesterol level of more than 160 milligrams per deciliter of
blood or an HDL-cholesterol level of less than 35 milligrams per deciliter.
Several factors add to the risk of heart disease in people with high
levels of LDL-cholesterol. These factors include a low HDL-cholesterol level, a family
history of premature heart disease, and being a male over 44 years of age or a female over
54. Individuals with two or more of these factors have high risk of heart attack,
particularly if they also have atherosclerosis (narrowing of the arteries because of fatty
Treatment of High Blood Cholesterol
This consists of first reducing the amount of saturated fat and
cholesterol in the diet. Poultry and fish are low in cholesterol. Cereals, fresh fruit,
and vegetables contain no cholesterol. Regular aerobic exercise--such as bicycling,
running, and swimming--can further lower the cholesterol level. Medication should be
considered only for people who are at high risk of heart disease and who have been unable
to control their cholesterol with diet. Medications shown to reduce cholesterol levels and
the risk of heart disease include cholestyramine, colestipol, gemfibrozil, lovastatin, and
Clinical research trials have indicated that lowering the amount of
cholesterol in the blood can reduce the risk of heart attack in middle-aged men who had no
history of heart disease. In men and women with atherosclerosis, reducing cholesterol in
blood prevents further narrowing of the heart arteries.