Free HealthE Newsletter

Cholesterol and Coronary Heart Disease

What Is Coronary Heart Disease?

Heart disease is caused by narrowing of the coronary arteries that feed the heart. Like any muscle, the heart needs a constant supply of oxygen and nutrients, which are carried to it by the blood in the coronary arteries. When the coronary arteries become narrowed or clogged by fat and cholesterol deposits and cannot supply enough blood to the heart, the result is coronary heart disease (CHD). If not enough oxygen-carrying blood reaches the heart, you may experience chest pain called angina. If the blood supply to a portion of the heart is completely cut off by total blockage of a coronary artery, the result is a heart attack. This is usually due to a sudden closure from a blood clot forming on top of a previous narrowing.

If you answer yes to any of these questions, you most probably have CHD.

• Have you ever had a heart attack?
• Do you suffer from chest pain that has been diagnosed as angina?
• Have you had heart surgery such as a bypass operation or a balloon or angioplasty procedure?
• Have you ever had an angiogram (a special x-ray picture of the heart) that showed a blockage in your coronary arteries?

You should be sure to talk to your doctor about cholesterol if you have answered yes to any of these questions.

Cholesterol is a waxy substance that occurs naturally in all parts of the body and that your body needs to function normally. It is present in cell walls or membranes everywhere in the body, including the brain, nerves, muscle, skin, liver, intestines, and heart. Your body uses cholesterol to produce many hormones, vitamin D, and the bile acids that help to digest fat. It takes only a small amount of cholesterol in the blood to meet these needs. However, if you have too much cholesterol in your bloodstream, it can lead to atherosclerosis, a condition in which fat and cholesterol are deposited in the walls of the arteries in many parts of the body, including the coronary arteries feeding the heart. In time, narrowing of the coronary arteries by atherosclerosis can produce the signs and symptoms of heart disease, including angina and heart attack.

The Framingham Heart Study established that high blood cholesterol is a risk factor for coronary heart disease (CHD). Results of the Framingham study showed that the higher the cholesterol level, the greater the CHD risk. On the other end of the spectrum, CHD is uncommon at total cholesterol levels below 150 milligrams per deciliter (mg/dL). A direct link between high blood cholesterol and CHD has been confirmed by the Lipid Research Clinics-Coronary Primary Prevention Trial (1984) which showed that lowering total and LDL ("bad") cholesterol levels significantly reduces CHD. A series of more recent trials of cholesterol lowering using statin drugs have demonstrated conclusively that lowering total cholesterol and LDL-cholesterol reduces the chance of having a heart attack, needing bypass surgery or angioplasty, and dying of CHD-related causes.

The Benefits of Cholesterol Lowering

A 1994 study called the Scandinavian Simvastatin Survival Study (also called 4S) found that lowering cholesterol can prevent heart attacks and reduce death in men and women who already have heart disease and high cholesterol. For over 5 years, more than 4,400 patients with heart disease and total cholesterol levels of 213 mg/dL to 310 mg/dL were given either a cholesterol-lowering drug or a placebo (a dummy pill that looks exactly like the medication). The drug they were given is known as a statin, and it reduced total cholesterol levels by 25 percent and LDL-cholesterol levels by 35 percent. The study found that in those receiving statin, deaths from heart disease were reduced by 42 percent, the chance of having a nonfatal heart attack was reduced by 37 percent, and the need for bypass surgery or angioplasty was reduced by 37 percent. A very important finding is that deaths from causes other than cardiovascular disease were not increased, and so the 42 percent reduction in heart disease deaths resulted in a 30 percent drop in overall deaths from all causes.

The 4S researchers say that the following benefits could be expected if doctors were to treat their heart disease patients for the same 5-year period and lower cholesterol to the same extent. For every 1,000 patients:

• 40 people would be saved out of the 90 who would otherwise die from heart disease.
• 70 of the expected 210 nonfatal heart attacks would be avoided.
• Heart procedures such as bypass surgery would be avoided in 60 of the 210 patients who would be expected to need these procedures.

In 1996 the results of the Cholesterol and Recurrent Events (CARE) Study also showed the benefits of cholesterol lowering in heart disease patients. This study reported that even in patients with seemingly normal cholesterol levels (average of 209 mg/dL), cholesterol lowering with a statin drug lowered the risk of having another heart attack or dying by 24 percent. These patients were also less likely to need bypass surgery (26 percent reduction) or angioplasty (22 percent reduction) during the study. Women benefited even more than men, reducing their risk of having another heart attack by 45 percent. The CARE researchers estimate that treatment of 1,000 patients similar to those in CARE would result in 153 fewer heart attacks and deaths from heart disease. If the patients were over 60, there would be 214 fewer, and if they were all women, there would be 248 fewer.

A study published in 1998, the Long-Term Intervention with Pravastatin in Ischaemic Disease (LIPID) study, examined the effects of cholesterol lowering in people with CHD (those who had already experienced a heart attack or had been hospitalized for angina) and who had relatively average cholesterol levels. The LIPID study used a statin drug to lower cholesterol levels in the treatment group. All study participants were counseled about following a cholesterol-lowering diet. The LIPID results showed that a drop of 18 percent in total cholesterol and 25 percent in LDL-cholesterol produced a 24 percent decrease in deaths from CHD among the treatment group compared with the control group. Similarly, cholesterol-lowering in the treatment group reduced the overall death rate by 22 percent, heart attacks by 29 percent, the need for bypass surgery or angioplasty by 20 percent, and stroke by 19 percent. Cholesterol lowering in the LIPID study resulted in significant reductions in CHD-related deaths and events without increasing non-CHD deaths.

These studies along with many others support the need to lower cholesterol levels in heart disease patients. If you lower your cholesterol, you too can see benefits like those in 4S, CARE, and LIPID.

Lipoproteins

Cholesterol travels in the blood in packages called lipoproteins. Just like oil and water, cholesterol, which is fatty, and blood, which is watery, do not mix. In order to be able to travel in the bloodstream, the cholesterol made in the liver is combined with protein, making a lipoprotein. This lipoprotein then carries the cholesterol through the bloodstream.

There are specific kinds of lipoproteins that contain cholesterol in your blood, and each affects your heart disease risk in a different way.

• LDL--"bad" cholesterol
• HDL--"good" cholesterol
• Triglyceride

What Makes Your Cholesterol High or Low?

Your blood cholesterol level is affected not only by what you eat but also by how quickly your body makes LDL-cholesterol and disposes of it. In fact, your body makes all the cholesterol it needs, and it is not necessary to take in any additional cholesterol from the foods you eat.

Patients with heart disease typically have too much LDL-cholesterol in their blood. Many factors help determine whether your LDL-cholesterol level is high or low. The following factors are the most important:

• Heredity

• What you eat

• Weight

• Physical activity/exercise

• Age and sex.

• Alcohol

• Stress

Heredity. Your genes influence how high your LDL-cholesterol is by affecting how fast LDL is made and removed from the blood. One specific form of inherited high cholesterol that affects 1 in 500 people is familial hypercholesterolemia, which often leads to early heart disease. But even if you do not have a specific genetic form of high cholesterol, genes play a role in influencing your LDL-cholesterol level.

What you eat. Two main nutrients in the foods you eat make your LDL-cholesterol level go up: saturated fat, a type of fat found mostly in foods that come from animals; and cholesterol, which comes only from animal products. Saturated fat raises your LDL-cholesterol level more than anything else in the diet. Eating too much saturated fat and cholesterol is the main reason for high levels of cholesterol and a high rate of heart attacks in the United States. Reducing the amount of saturated fat and cholesterol you eat is a very important step in reducing your blood cholesterol levels.

Weight. Excess weight tends to increase your LDL-cholesterol level. If you are overweight and have a high LDL-cholesterol level, losing weight may help you lower it. Weight loss also helps to lower triglycerides and raise HDL.

Physical activity/exercise. Regular physical activity may lower LDL-cholesterol and raise HDL-cholesterol levels.

Age and sex. Before menopause, women usually have total cholesterol levels that are lower than those of men the same age. As women and men get older, their blood cholesterol levels rise until about 60 to 65 years of age. In women, menopause often causes an increase in their LDL-cholesterol and a decrease in their HDL- cholesterol level, and after the age of 50, women often have higher total cholesterol levels than men of the same age.

Alcohol. Alcohol intake increases HDL-cholesterol but does not lower LDL-cholesterol. Doctors don't know for certain whether alcohol also reduces the risk of heart disease. Drinking too much alcohol can damage the liver and heart muscle, lead to high blood pressure, and raise triglycerides. Because of the risks, alcoholic beverages should not be used as a way to prevent heart disease.

Stress. Stress over the long term has been shown in several studies to raise blood cholesterol levels. One way that stress may do this is by affecting your habits. For example, when some people are under stress, they console themselves by eating fatty foods. The saturated fat and cholesterol in these foods contribute to higher levels of blood cholesterol.

Unstable Plaque

Cholesterol is a major ingredient of the plaque that builds up in the coronary arteries and causes heart disease, so it is important to understand how plaques develop. Excess cholesterol is deposited in the artery walls as it travels through the bloodstream. Then, special cells in the artery wall gobble up this excess cholesterol, creating a "bump" in the artery wall. This cholesterol-rich "bump" then is covered by a scar that produces a hard coat or shell over the cholesterol and cell mixture. It is this collection of cholesterol covered by a scar that is called plaque. 

The plaque buildup narrows the space in the coronary arteries through which blood can flow, decreasing the supply of oxygen and nutrients to the heart. If not enough oxygen- carrying blood can pass through the narrowed arteries to reach the heart muscle, the heart may respond with a pain called angina. The pain usually happens with exercise when the heart needs more oxygen. It is typically felt in the chest or sometimes in other places like the left arm and shoulder. However, this same inadequate blood supply may cause no symptoms. 

Plaques come in various sizes and shapes. Throughout the coronary arteries many small plaques build themselves into the walls of the arteries, blocking less than half of the artery opening. These small plaques are often invisible on many of the tests doctors use to identify coronary heart disease. It used to be thought that the most dangerous plaques and the ones most likely to cause total blockage of coronary arteries were the largest ones. The largest plaques are in fact the ones most likely to cause angina. However, small plaques that are full of cholesterol and covered by a scar are now thought to be very unstable and more likely to rupture or burst, releasing their cholesterol contents into the bloodstream. When this happens, it triggers blood clotting inside the artery. If the blood clot totally blocks the artery, it stops blood flow and a heart attack occurs. The muscle on the far side of the blood clot does not get enough oxygen and begins to die. The damage can be permanent. 

Lowering your blood cholesterol level can slow, stop, or even reverse the buildup of plaque. Cholesterol lowering can reduce your risk of a heart attack by lowering the cholesterol content in unstable plaques to make them more stable and less prone to rupture. This is why lowering your LDL-cholesterol is such an important way to reduce your risk for having a heart attack. Even in people who have had one heart attack, the chances of having future attacks can be substantially reduced by cholesterol lowering.

National Heart, Lung, and Blood Institute

Path: Home>Education>Food and Nutrition Information>Cholesterol and Coronary Heart Disease