Atherosclerosis is caused by repeated injury to the walls of arteries.
Many factors contribute to this injury, including high blood pressure, tobacco smoke, diabetes, and high levels of cholesterol in the blood.
Blood vessel blockage due to atherosclerosis is a common cause of heart attack and stroke.
Often, the first symptom is pain or cramps at times when blood flow cannot keep up with the tissues' need for oxygen.
To prevent atherosclerosis, people need to stop using tobacco, improve their diet, exercise regularly, and maintain control of their blood pressure, cholesterol level, and diabetes.
Progression of atherosclerosis to such life-threatening complications as a heart attack or stroke requires emergency treatment.
In the United States and most other developed countries, atherosclerosis is the leading cause of illness and death. In 2016, cardiovascular disease, primarily coronary artery disease (atherosclerosis that affects the arteries supplying blood to the heart) and stroke (atherosclerosis affecting the arteries to the brain —see figure Supplying the Brain With Blood), caused almost 18 million deaths worldwide, making atherosclerosis the leading cause of death worldwide.
Atherosclerosis can affect the medium-sized and large arteries of the brain, heart, kidneys, other vital organs, and legs. It is the most important and most common type of arteriosclerosis.
Arteriosclerosis, which means hardening (sclerosis) of the arteries (arterio-), is a general term for several disorders in which the wall of an artery becomes thicker and less elastic. There are three types:
Atherosclerosis, the most common type, means hardening related to plaques, which are deposits of fatty materials. It affects medium-sized and large arteries.
Arteriolosclerosis means hardening of the arterioles, which are small arteries. It affects primarily the inner and middle layers of the walls of arterioles. The walls thicken, narrowing the arterioles. As a result, organs supplied by the affected arterioles do not receive enough blood. The kidneys are often affected. This disorder occurs mainly in people who have high blood pressure or diabetes. Either of these disorders may stress the walls of arterioles, resulting in thickening.
Mönckeberg arteriosclerosis affects small to medium-sized arteries. Calcium accumulates within the walls of arteries, making them stiff but not narrow. This essentially harmless disorder usually affects men and women older than 50.
The development of atherosclerosis is complicated, but the primary event seems to be repeated, subtle injury to the artery's inner lining (endothelium), through various mechanisms. These mechanisms include
Physical stresses from turbulent blood flow (such as occurs where arteries branch, particularly in people who have high blood pressure)
Inflammatory stresses involving the immune system (such as when people smoke cigarettes)
Infections with some bacteria or viruses (such as Chlamydia pneumoniae or cytomegalovirus) may also increase inflammation in the artery's inner lining (endothelium) and lead to atherosclerosis.
Atherosclerosis begins when the injured artery wall creates chemical signals that cause certain types of white blood cells (monocytes and T cells) to attach to the wall of the artery. These cells move into the wall of the artery. There they are transformed into foam cells, which collect cholesterol and other fatty materials and trigger growth of smooth muscle cells in the artery wall. In time, these fat-laden foam cells accumulate. They form patchy deposits (atheromas, also called plaques) covered with a fibrous cap in the lining of the artery wall. With time, calcium accumulates in the plaques. Plaques may be scattered throughout medium-sized and large arteries, but they usually start where the arteries branch.
How Atherosclerosis Develops
Plaques can grow into the opening (lumen) of the artery, gradually causing it to narrow. When atherosclerosis narrows an artery, tissues supplied by the artery may not receive enough blood and oxygen. Plaques also can grow into the wall of the artery, where they do not block blood flow. Both kinds of plaques can split open (rupture), exposing the material within to the bloodstream. This material triggers blood clot formation. These blood clots can suddenly block all blood flow through the artery, which is the main cause of a heart attack or stroke. Sometimes these blood clots break off, travel through the bloodstream, and block an artery elsewhere in the body. Similarly, pieces of the plaque can break off and travel through the bloodstream and block an artery elsewhere.
Some risk factors for atherosclerosis can be modified (see also Prevention of coronary artery disease).
Modifiable risk factors include
Risk factors that cannot be modified include
There are many risk factors that are still being studied, such as high levels of C-reactive protein (an inflammatory protein) in the blood, high levels of some components of cholesterol such as apolipoprotein B or lipoprotein(a), and psychosocial factors (such as anxiety and low socioeconomic status).
One of the most important modifiable risk factors is smoking. (Using other forms of tobacco, such as snuff and chewing tobacco, also increases risk.) A smoker‘s risk of developing some forms of atherosclerosis such as coronary artery disease is directly related to the amount of tobacco smoked daily. The risk of a heart attack is increased threefold in men and sixfold in women who smoked 20 or more cigarettes per day compared with nonsmokers. In people who already have a high risk of heart disease, tobacco use is particularly dangerous.
Tobacco use decreases the level of high-density lipoprotein (HDL) cholesterol—the “good” cholesterol—and increases the level of low-density lipoprotein (LDL) cholesterol—the “bad” cholesterol. Smoking increases the level of carbon monoxide in the blood, which may increase the risk of injury to the lining of the artery‘s wall. Tobacco use causes arteries already narrowed by atherosclerosis to constrict, further decreasing the amount of blood reaching the tissues. In addition, tobacco use increases the blood‘s tendency to clot (by making platelets stickier), so that it increases the risk of peripheral arterial disease (atherosclerosis affecting arteries other than those that supply the heart and brain), coronary artery disease, stroke, and blockage of an arterial graft placed during coronary artery bypass surgery or surgery to bypass a blocked artery elsewhere in the body.
People who quit using tobacco have only half the risk of those who continue to use tobacco—regardless of how long they smoked before quitting. Quitting also decreases the risk of death after coronary artery bypass surgery or a heart attack and the risk of illness and death in people who have peripheral arterial disease. The benefits of quitting tobacco use begin immediately and increase with time.
Secondhand smoke (smoke breathed in from someone else‘s smoking) appears to increase risk also. It should be avoided.
A high level of LDL cholesterol is another important modifiable risk factor. A diet that is high in saturated fats (see Types of Fat) causes LDL cholesterol levels to increase in susceptible people. Cholesterol levels also increase as people age and are normally higher in men than in women, although levels increase in women after menopause. Several hereditary disorders result in high levels of cholesterol or other fats. People with these hereditary disorders can have extremely high levels of cholesterol and (if untreated) die of coronary artery disease at an early age.
Lowering high LDL cholesterol levels through the use of drugs can significantly reduce the risk of heart attacks, strokes, and death. Many types of lipid-lowering drugs are available (see table Lipid-Lowering Drugs). Statins are the most common type.
Not all high cholesterol levels increase the risk of atherosclerosis. A high level of HDL (good) cholesterol decreases the risk of atherosclerosis.
The desired level of total cholesterol, which includes LDL cholesterol, HDL cholesterol, and triglycerides, is 140 to 200 mg/dL (3.6 to 5.2 mmol/L). Risk of a heart attack more than doubles when the total cholesterol level approaches 300 mg/dL (7.8 mmol/L). The risk is decreased when the LDL cholesterol level is below 130 mg/dL (3.4 mmol/L), and the HDL cholesterol level is above 40 mg/dL (1 mmol/L).
High-risk people, such as those who have diabetes or atherosclerotic heart disease or have had a heart attack, stroke, or bypass surgery, benefit from high doses of statins to lower their LDL cholesterol as much as possible. However, the percentage of HDL cholesterol in relation to total cholesterol is a more reliable measure of risk than is the total or LDL cholesterol level. HDL cholesterol should account for more than 25% of total cholesterol. High triglyceride levels are often associated with low HDL cholesterol levels. However, evidence suggests that high triglyceride levels alone may also slightly increase the risk of atherosclerosis.
Uncontrolled high blood pressure is a risk factor for heart attack and stroke, which are caused by atherosclerosis. The risk of cardiovascular disease starts increasing when blood pressure levels are above 110/75 mm Hg. Reducing high blood pressure clearly lowers risk. Doctors usually try to achieve a blood pressure of less than 140/90 mm Hg, and often less than 130/80 mm Hg in people at risk of cardiovascular disease, such as people with diabetes or kidney disease.
People who have diabetes mellitus tend to develop disease that affects small arteries, such as those in the eyes, nerves, and kidneys, leading to vision loss, nerve damage, and chronic kidney disease. People with diabetes also tend to develop atherosclerosis in large arteries. Atherosclerosis tends to develop at an earlier age and more extensively than it does in people who do not have diabetes. The risk of developing atherosclerosis is 2 to 6 times higher for people with diabetes, particularly women. Women who have diabetes, unlike those who do not, are not protected from atherosclerosis before menopause. People who have diabetes have the same risk of death as someone who has had a prior heart attack, and doctors usually try to help these people keep other risk factors (such as high cholesterol levels and high blood pressure) under careful control.
Obesity, particularly abdominal (truncal) obesity, increases the risk of coronary artery disease (atherosclerosis of the arteries that supply blood to the heart). Abdominal obesity increases the risk of other risk factors for atherosclerosis: high blood pressure, type 2 diabetes, and high cholesterol levels. Losing weight reduces the risk of all these disorders.
Physical inactivity appears to increase the risk of developing coronary artery disease, and much evidence suggests that regular exercise even to a moderate degree reduces this risk and decreases mortality. Exercise can also help modify other risk factors for atherosclerosis—by lowering blood pressure and cholesterol levels and by helping with weight loss and decreasing insulinresistance.
There is substantial evidence that regular vegetable and fruit consumption can decrease the risk of coronary artery disease. It is unclear whether fruits and vegetables appear beneficial due to the substances (phytochemicals) they contain, or whether people who eat a lot of fruits and vegetables also eat less saturated fat and are more likely to take fiber and vitamins. However, phytochemicals called flavonoids (in red and purple grapes, red wine, black teas, and dark beers) appear especially protective. High concentrations in red wine may help explain why the French have a relatively low incidence of coronary artery disease, even though they use more tobacco and consume more fat than Americans do. But no studies prove that eating flavonoid-rich foods or using supplements instead of foods prevents atherosclerosis.
Increased fiber content in certain vegetables may decrease total cholesterol and may decrease blood glucose and insulin levels. However, excessive fiber interferes with the absorption of certain minerals and vitamins. In general, foods rich in phytochemicals and vitamins are also rich in fiber.
Fat is an essential part of the diet. The notion that eating less fat is important to a healthy diet is only partly true because the type of fat also matters. The main types of fats are
Saturated and trans fats
Unsaturated fats (polyunsaturated and monounsaturated—see Types of Fat)
Fats may be soft (or liquid) or firm at room temperature. Soft fats, such as oils and some margarines, tend to be higher in polyunsaturated and monounsaturated fats. Hard fats, such as butter and shortening, tend to be higher in saturated and trans fats. Saturated and trans fats are more likely to cause atherosclerosis. Thus, whenever possible, people should limit the amount of saturated and trans fats in their diet and choose foods with monounsaturated or polyunsaturated fats instead. Saturated and trans fats are found in red meat, many fast food and junk food items, full-fat dairy products (such as cheese, butter, and cream), and hard (stick) margarines. However, the evidence regarding dangers of natural trans fats remains unclear. Monounsaturated fats are found in canola and olive oil, soft margarines with no trans fat, nuts, and olives. Polyunsaturated fats are found in nuts, seeds, oils, and mayonnaise.
Two types of polyunsaturated fats—omega-3 and omega-6 fats—are essential to a healthy diet. Omega-3 fats are found in fatty fish such as salmon, omega-3 eggs, canola oil, and walnuts. Omega-6 fats are found in some nuts and seeds and in safflower, sunflower, and corn oils.
Eating a healthy diet can help decrease the risk of atherosclerosis. However, it is less clear whether supplementing the diet with vitamins, phytochemicals, trace minerals, or coenzyme Q10 also helps reduce the risk.
People who drink a moderate amount of alcohol seem to have a lower risk of coronary artery disease than do people who drink too much or do not drink at all. Alcohol increases the level of HDL cholesterol (good cholesterol), and it also decreases the risk of blood clots and inflammation and helps protect the body from the by-products of cell activity. However, more than moderate alcohol consumption (more than 14 drinks per week for men and more than 9 drinks per week for women) can cause significant health problems and increase the risk of death. People who drink greater amounts of alcohol should cut back. People who do not drink alcohol should not start.
People who have very high levels of homocysteine (an amino acid) in their blood, usually because of a hereditary disorder, have an increased risk of coronary artery disease, usually at a young age. However, it is unclear why high homocysteine levels are associated with atherosclerosis. Giving people drugs that lower homocysteine levels does not seem to reduce risk of death.
Symptoms depend on
With gradual narrowing, atherosclerosis usually does not cause symptoms until the interior of an artery is narrowed by more than 70%.
The first symptom of a narrowed artery may be pain or cramps at times when blood flow cannot keep up with the tissues’ need for oxygen. For instance, during exercise, a person may feel chest pain or discomfort because the oxygen supply to the heart is inadequate. This chest pain (angina) goes away within minutes after the person stops exertion. While walking, a person may feel leg cramps (intermittent claudication) because the oxygen supply to the leg muscles is inadequate. If the arteries supplying one or both kidneys become narrowed, kidney failure or dangerously high blood pressure can result.
How atherosclerosis is diagnosed depends on whether the person is having symptoms.
People who have symptoms that suggest a blocked artery have tests to look for the location and extent of the blockage. Different tests are used depending on what organ seems to be involved. For example, if doctors suspect blockage of an artery in the heart, they typically do electrocardiography (ECG), blood tests for substances (cardiac markers) that indicate heart damage, and sometimes a stress test or heart catheterization.
People with atherosclerotic arteries in one organ often have atherosclerosis in other arteries. Therefore, when doctors find atherosclerotic blockage in one artery, for example in the leg, they usually do tests to look for blockage in other arteries, such as those in the heart.
Doctors also test for certain risk factors in people who have an atherosclerotic blockage. For example, they measure the levels of glucose, cholesterol, and triglycerides in the blood. Doctors usually also do these tests as part of the routine yearly examination in adults.
Because some plaques in arteries are more likely to break open and trigger a clot than others, doctors sometimes do tests to look for such dangerous plaques. No test is definitive, but doctors are using computed tomography (CT) angiography, intravascular ultrasonography (which uses an ultrasound probe on the tip of a catheter placed inside of an artery) during heart catheterization and coronary angiography, and a number of other imaging tests and blood tests.
In people who have some risk factors for atherosclerosis but no symptoms, doctors usually do blood tests to measure the levels of glucose, cholesterol, and triglycerides in the blood. Doctors usually also do these tests as part of the routine yearly examination in adults.
Some doctors recommend imaging tests to look for atherosclerotic blockage in people who have risk factors but no symptoms as part of a prevention strategy. Such tests include an electron beam CT of the heart and ultrasonography of the arteries in the neck (carotid arteries). CT can also be used to detect hardened (calcified) plaque in the coronary arteries. The result of this test is sometimes called the calcium score. Ultrasonography of the carotid arteries can detect thickening of the artery wall, which suggests atherosclerosis. However, many doctors think that these tests rarely change the advice they would give based on the person‘s other, more easily recognized, risk factors.
To help prevent atherosclerosis, people need to
Eating a healthy diet can help decrease the risk of atherosclerosis. A diet low in saturated fats, refined carbohydrates, and alcohol and high in fruits, vegetables, and fiber decreases the risk of cardiovascular disease. Healthy diet and exercise can promote weight loss if a person is overweight or obese.
People who smoke should stop smoking. People who quit using tobacco have only half the risk of those who continue to use tobacco—regardless of how long they smoked before quitting.
People who have high blood pressure should lower their blood pressure with lifestyle changes and drugs. People who have diabetes must maintain strict control of their blood sugar (glucose).
People who are at high risk of atherosclerosis also may benefit from taking certain drugs. Helpful drugs include the statins, which lower cholesterol (even if cholesterol levels are normal or only slightly high), and in some cases, aspirin or other antiplatelet drugs (drugs that keep platelets from sticking together and forming blockages in blood vessels). Aspirin and other antiplatelet drugs can cause bleeding so these drugs should only be taken if patients are at very high risk of atherosclerosis. Some drugs used to treat high blood pressure and some drugs used to treat diabetes also help reduce risk of atherosclerosis.