Stroke Causes and Risk Factors
Ischemic stroke occurs when blood flow through a blood vessel (artery) that supplies blood to the brain is blocked. Blockage may develop from a blood clot in an artery leading to the brain (thrombus) or one formed in another part of the body, usually the heart (embolus). The clot travels with the blood until it blocks an artery in the brain. These blood clots usually are the result of irregular heartbeat, heart valve problems, infection of the heart muscle, hardening of the arteries, blood-clotting disorders, inflammation of the blood vessels or heart attack.
A less common cause of ischemic stroke occurs when blood pressure becomes too low (hypotension), reducing blood flow to the brain. This usually occurs with narrowed or diseased arteries. Low blood pressure can result from a heart attack, large loss of blood or severe infection. Each of these conditions affects the flow of blood through the heart and blood vessels and increases the risk of stroke. Additionally, surgery to correct narrowed or blocked arteries in the neck may sometimes cause a stroke.
Hemorrhagic stroke is caused by sudden bleeding from a blood vessel inside the brain (cerebral hemorrhage) or in the spaces around the brain (subarachnoid hemorrhage). Sudden bleeding may result from the bursting of a blood vessel that has stretched and thinned (aneurysm). The most common cause of bleeding inside the brain is high blood pressure.
Uncommon causes of hemorrhagic stroke include inflamed blood vessels, which may develop from syphilis or tuberculosis, blood-clotting disorders, head or neck injuries, radiation treatment for cancer or cerebral amyloid angiopathy(a condition in which a protein substance builds up and weakens the blood vessels in the brain, causing bleeding and a stroke).
Over the past several decades, doctors have learned more and more about the factors that lead to strokes.
The American Heart Association has identified several factors that increase your risk of stroke. The more risk factors you have, the greater your chances for a stroke.
These factors fall into two categories: 1) factors that cannot be modified, and 2) factors that you can modify by changes in your lifestyle. Your personal healthcare provider can help you assess your risk for stroke and recommend ways to control your risk factors and reduce your risk of getting a stroke.
Risk factors that you cannot modify include:
- Age. While strokes can happen to a person of any age, even children, the older you are, the more at risk of having a stroke you are.
- Gender. While more men than women have strokes, more women die from strokes. More than half of the total deaths from stroke occur in women. Using birth control pills and being pregnant are special concerns for women.
- Race. African Americans have a much higher risk of death from a stroke than Caucasians. This may be due to blood pressure, diabetes and obesity.
- Family History. Your stroke risk is greater if a parent, grandparent, sister or brother has had a stroke.
- Personal health and medical history. Someone who has had a stroke is at much higher risk of having another one. If you have had a heart attack, you are at higher risk of having a stroke, too.
Risk factors that you can modify include:
- High blood pressure. High blood pressure is defined in an adult as a systolic pressure of 140 mm Hg or higher and/or a diastolic pressure of 90 mm Hg or higher for an extended time. It is the most important risk factor for stroke.
- Diabetes mellitus. While diabetes is treatable, having it still increases a person’s risk of stroke. People with diabetes often also have high blood pressure, high blood cholesterol and are overweight. This increases their risk even more. If you have diabetes, work closely with your doctor to manage it.
- Carotid or other artery disease. The carotid arteries in your neck supply blood to your brain. A carotid artery narrowed by fatty deposits from atherosclerosis may become blocked by a blood clot. People with peripheral artery disease have a higher risk of carotid artery disease, which raises their risk of stroke. Peripheral artery disease is the narrowing of blood vessels carrying blood to leg and arm muscles. It is caused by atherosclerosis.
- Atrial fibrillation. This heart rhythm disorder raises the risk for stroke because the heart’s upper chambers quiver instead of beating effectively. This lets the blood pool and clot. If a clot breaks off, enters the bloodstream and lodges in an artery leading to the brain, a stroke results.
- Other heart diseases. People with coronary heart disease or heart failure have more than twice the risk of stroke as those with hearts that work normally. Dilated cardiomyopathy (an enlarged heart), heart valve disease and some types of congenital heart defects also increase the risk of stroke.
- Transient ischemic attacks (TIAs). TIAs are “mini-strokes” that produce stroke-like symptoms but no lasting damage. Recognizing and treating TIAs can reduce your risk of a major stroke. Call 911 to get medical help immediately if they occur!
- Certain blood disorders. A high red blood cell count thickens the blood and makes clots more likely. This raises the risk of stroke. Doctors may treat this problem by removing blood cells or prescribing “blood thinners.” Another blood disorder, sickle cell anemia, mainly affects African Americans. In this condition, sickle-shaped red blood cells are less able to carry oxygen to the tissues and organs. They also tend to stick to the blood vessel walls, which in turn can block arteries to the brain and cause a stroke.
- High blood cholesterol. A high level of total cholesterol in the blood (240 mg/dL or higher) is a major risk factor for heart disease, which raises your risk of stroke. Recent studies show that high levels of LDL cholesterol (greater than 100 mg/dL) and triglycerides (blood fats) directly increase the risk of stroke in people with previous coronary heart disease, ischemic stroke or transient ischemic attack (TIA). Low levels of HDL cholesterol (less than 40 mg/dL) also may raise stroke risk.
Lifestyle changes that can reduce your risk of stroke include:
- Stop using tobacco. Cigarette smoking is the top preventable risk factor for stroke. Both the nicotine and carbon monoxide found in tobacco smoke lower the amount of oxygen in your blood. They also damage the walls of blood vessels, making clots more likely to form. Combining the use of some kinds of birth control pills with smoking greatly increases a woman’s stroke risk.
- Maintain a proper weight and exercise. Being inactive, obese or both can increase your risk of high blood pressure, high blood cholesterol, diabetes, heart disease and stroke.
- Drink moderately. An average of more than one alcoholic drink a day for women or more than two drinks a day for men raises blood pressure and can lead to stroke.
- Illegal drug abuse. Intravenous drug abuse carries a high risk of stroke. Cocaine use has been linked to strokes and heart attacks. Some have been fatal even in first-time users.