The Comprehensive Stroke Center at University Hospital
Risk Factors for Stroke
There is good news regarding our ability to avoid stroke or significantly reduce the likelihood one will occur. Many of the risk factors for stroke are preventable or controllable.
Studies show that a healthy lifestyle and diet along with preventive medical care where appropriate can significantly reduce the risk of suffering a stroke. By modifying certain behaviors and getting treatment for risky medical conditions, we can prevent or control many of the conditions that commonly lead to stroke.
More than 80 percent of strokes could be eliminated, according to current estimates, if people recognized and reduced their risks!
Common risk factors for stroke include:
Manageable or Preventable Risk Factors
- Diet & Nutrition
- Physical Inactivity
- Substance/Alcohol Abuse
- Certain medical conditions, including:
- Abnormal blood vessel connections (arteriovenous malformations and arteriovenous fistulas)
- Cerebral aneurysms (unruptured)
- Cholesterol level (high levels of “bad” cholesterol and/or low levels of “good” cholesterol)
- Hardening of the arteries (atherosclerosis/arteriosclerosis)
- Heart (cardiovascular) disease
- High blood pressure (hypertension)
- Transient ischemic attacks (TIAs)
Unalterable Risk Factors
- Heredity/family history of stroke
Risk Factors We Can Prevent or Manage
Which of the preventable/manageable risk factors contribute the most to stroke? It is difficult to say because so many of them are inextricably interconnected. For example, overeating and a sedentary lifestyle can lead to harmful medical conditions such as hypertension, high levels of bad cholesterol and obesity – all of which have been linked to stroke.
It is no coincidence that many of the conditions linked to increased risk of stroke are also major contributors to heart attack. There is a direct correlation between cardiovascular disease and cerebrovascular disease.
Diet & Nutrition: A high level of “bad” cholesterol in the bloodstream is a major risk factor for stroke. The primary way that cholesterol enters our bodies is through fats in the food we consume, which is why a sensible, balanced diet is so important.
Studies also link high levels of sodium (salt) in the diet – already known to increase blood pressure – with increased risk of stroke.
Physical Activity: Physical activity helps control many of the risk factors associated with stroke, while lack of physical activity can contribute to them. By improving blood circulation, exercise enhances the body’s ability to use oxygen, which helps to reduce blood pressure. Regular physical activity has been shown to increase “good” cholesterol levels, decrease triglyceride (body fat) levels, and help manage body weight (prevent obesity).
Smoking: Smoking increases your chances of suffering all types of stroke. A study published in the May 2003 issue of Stroke, a journal of the American Heart Association, shows that the risk of stroke increases incrementally depending on how many cigarettes a day you smoke. Nicotine (the addictive element in cigarettes) raises blood pressure and the likelihood of developing hypertension. Cigarette smoke — which contains more than 4,000 chemicals, including 43 known to cause cancer — thickens the blood, making it more likely to clot.
Even environmental tobacco smoke (ETS), or secondhand smoke, has been linked to increased risk of stroke because it contains the same harmful chemicals that smokers inhale. ETS includes mainstream smoke – the smoke that is drawn through the mouthpiece of a cigarette then exhaled into the air by the smoker – and sidestream smoke, which comes from the burning tobacco in cigarettes.
Substance Abuse: The use of certain illegal or controlled substances has been shown to increase the risk of stroke — particularly hemorrhagic stroke. Cocaine (“crack” in its smoked form) causes a severe elevation of blood pressure that can rupture a blood vessel leading to or inside of the brain. Smoked amphetamines — such as crystal meth and ice — as well as any illicit drug injected into the bloodstream also can produce stroke.
Among adolescents and young adults, an increasing percentage of strokes occur in relation to drug use.
Alcohol Consumption: Heavy and regular use of alcohol can dramatically increase your blood pressure. Studies suggest that heavy alcohol use, defined as two drinks or more a day, may increase more than tenfold the chances of suffering a subarachnoid hemorrhage (SAH).
Obesity: Obesity increases the chance of suffering hypertension and high blood cholesterol, both of which are significant factors in stroke. Some research suggests that even modest weight gain over the ideal weight, such as 24 to 43 pounds over 16 years, doubles the chances of suffering a stroke.
Medical Conditions & General Health
Abnormal Blood Vessel Connections: Abnormalities within cerebral arteries and veins include arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs). AVMs and AVFs, also called lesions, are abnormal connections between cerebral arteries (which carry blood to the brain) and veins (which take blood away from the brain).
|Angiogram demonstrating an AVF. In this case, the middle meningeal artery has a direct connection with the basilar artery.|
AVMs are masses of arteries and veins without intervening capillaries. Arteries decrease in size the farther they are from the heart. Ultimately they become so small that they are called capillaries. Capillaries are large enough to allow only one or two red blood cells to flow through them at a time. The decrease in the size of arteries from the heart to the capillaries is accompanied by a large decrease in the pressure within them at these locations. Veins form from the joining of capillaries, and they transport blood back to the heart under low pressure.
In AVMs, because there are no capillaries, high-pressure arterial blood empties directly into veins, which have thin walls capable of containing only low pressure. The stress of the pressure can cause a vein to rupture, resulting in hemorrhage. The other clinically significant consequence of arterial blood flowing directly into veins without intervening capillaries is that the tissues through which the blood flows cannot adequately extract oxygen and nutrients necessary for their functioning and survival. This can result in seizure or stroke.
|Illustration of the normal transition of blood flow from arteries to veins.|
|Illustration of Arteriovenous Malformation (AVM) which results from direct flow of blood under pressure from the artery to the vein. This results in the development of the AVM. Note the dilitation and twisting of the vessel.|
AVMs appear to be acquired prior to birth (congenital) and tend to form near the back of the brain. Although AVFs can be congenital, more often they are caused by a trauma that damages an artery and a vein which are side by side in the brain.
These blood vessel abnormalities can cause a host of problems, but the two most common are pressure against the adjacent parts of the brain, causing neurological problems (such as seizures, paralysis or loss of speech); and, bleeding (hemorrhage) into surrounding tissues. Hemorrhage from cerebral arteriovenous abnormalities represents from 2 percent to 4 percent of all strokes.
There are three general forms of treatment for AVMs/AVFs:
This is the best-known and longest-standing treatment
for AVMs. It involves entering the skull and tying
off or clipping the arterial vessels that feed the
malformation, eliminating the draining veins, and
removing or obliterating the nest (nidus) of the AVM.
- Endovascular Embolization.
This involves closing off the vessels of the AVM or
AVF by injecting an agent into them — such as
a special glue or a tiny coil or balloon — to
block blood flow through the abnormal connection.
Embolization is often used before surgery to minimize
blood loss, making the operation safer and shorter.
It can also be performed before radiosurgery to make
the AVM smaller and increase the chance that radiosurgery
will be successful. In some cases, endovascular embolization
alone can permanently cure an AVM.
- Radiosurgery. Despite its name, radiosurgery does not require any surgical instruments to be placed within the head. This procedure tightly focuses beams of radiation from outside the skull onto the abnormal vessels in order to injure and clog the AVM. The vessels gradually close off and are replaced with scar tissue. The results of radiosurgery can take from weeks to years to become fully effective. A danger of radiosurgery is damage to normal brain or spinal cord tissue around the AVM. Therefore, the procedure is usually reserved for AVMs that are relatively small (less than 3 cm in diameter), are situated so deep beneath important brain tissue that the surgical approach is hazardous, or involve so many vessels that embolization is not feasible.
|Cerebral angiogram 3D reconstruction showing an unruptured aneurysm.|
Cerebral Aneurysm (Unruptured): A brain aneurysm is a weak bulging spot on the wall of a brain artery very much like a thin balloon or weak spot on an inner tube. Aneurysms form from wear and tear on the arteries, and sometimes from injury, infection or an inherited tendency. The primary risk a cerebral aneurysm poses is that it will leak or rupture, resulting in hemorraghic stroke. Patients often experience no symptoms before a rupture occurs. In these cases, the aneurysm may be discovered incidentally, perhaps during an angiogram for carotid artery disease.
But sometimes, as an aneurysm grows, it compresses surrounding nerves and brain tissue, causing functional problems. In about 40 percent of cases, people with unruptured aneurysms experience some or all of the following symptoms:
- Peripheral vision deficits
- Thinking or processing problems
- Speech complications
- Perceptual problems
- Sudden changes in behavior
- Loss of balance and coordination
- Decreased concentration
- Short-term memory difficulty
Regardless of their size or whether they are producing symptoms, all aneurysms need prompt evaluation by a neurosurgeon. Appropriate treatment depends on the size and location of the aneurysm and the patient’s medical history. The risk of rupture increases with the size of the aneurysm and time. Evidence suggests that the risk of rupture for most unrepaired small aneurysms (less than 7 millimeters in size) is small.
The most common treatment for both unruptured and ruptured aneurysms is surgical clipping. The surgeon opens the cranium and blocks the blood flow into the aneurysm by applying a metal clip to its base (neck) where it connects to the blood vessel. This redirects the blood flow along its proper route. A newer, less invasive option is endovascular coiling or coil embolization. A tiny platinum coil is delivered to the site of the aneurysm through a catheter and deployed into the aneurysm, blocking blood flow into the aneurysm and preventing rupture (or re-rupture).
Cholesterol Levels: Although it gets a lot of bad press, the waxy, fatty substance called cholesterol is necessary for healthy cell membranes, among other things. We manufacture cholesterol naturally in our liver and we also get it through our diet.
There are different types of cholesterol and while our bodies use both, one — HDL (high-density lipoprotein) — is considered “good” and another — LDL (low-density lipoprotein) — "bad". Good cholesterol (HDL) carries bad cholesterol (LDL) away from the arteries. Bad cholesterol (LDL) can combine with other substances in the blood to form plaque, which can stick to the artery walls — potentially leading to clots that can result in ischemic stroke.
Some people are genetically predisposed to bad-cholesterol buildup. Their liver produces too much LDL. But in most cases, people bring on the problem themselves through bad behaviors, such as smoking and lack of physical activity. A primary cause is a diet high in saturated, polyunsaturated and/or hydrogenated fats (trans fatty acids) and/or low in monosaturated fats, which appear to reduce bad cholesterol without affecting good cholesterol.
Modification of bad behaviors can help maintain cholesterol levels within the normal range — less than 200 mg/dL (measured in milligrams per deciliter of blood). When that is not enough, physicians also can prescribe appropriate medications to control cholesterol levels.
Cholesterol Medications. The most prominent cholesterol drugs are in the statin family. They work by interfering with the cholesterol-producing mechanisms of the liver and by increasing the capacity of the liver to remove cholesterol from circulating blood (by producing more HDL). They include lovastatin (Mevacor®), fluvastatin (Lescol®), pravastatin (Pravachol®), simvastatin (Zocor®), atorvastatin (Lipitor®) and the newest, rosuvastatin (Crestor®). [A seventh statin, cervastatin (Baycol™), is no longer available.]
Other drug treatments include:
- nicotinic acid (niacin), which lowers LDL levels and raises HDL but must be given in large doses that can potentially be toxic;
- resins, such as Questran (cholestyramine) and Colestid (colestipol), which increase can increase HDL levels, and therefore the liver’s uptake of cholesterol from the bloodstream;
- fibric acid derivatives, such as Lopid (gemfibrozil) and Tricor (fenofibrate), which can also increase HDL levels; and
- aspirin, which can thin the blood and reduce the possibility of clot formation.
Diabetes: People with diabetes are two to four times more likely to suffer strokes. Diabetes impedes the body’s ability to produce or properly use insulin — a hormone that allows our cells to absorb glucose, our body’s main source of fuel. Glucose is created naturally during the digestive process, and our pancreas is supposed to automatically produce the right amount of insulin to allow our bodies to use the glucose. In diabetics, the pancreas produces little or no insulin, so glucose builds up to high levels in the blood.
The disease falls into two main categories: type 1, which usually occurs during childhood or adolescence; and type 2, the most common form that generally occurs after age 45. There is also gestational diabetes, which can occur during pregnancy.
Diabetes can seriously harm blood vessels throughout the body, including those in the brain, which increases the risk of stroke. High blood glucose levels can cause hardening of the arteries (atherosclerosis), thicken capillary walls and make blood stickier — all significant risk for ischemic stroke. It can also cause small vessels to leak, reducing blood flow to the body tissue.
If blood sugar (glucose) levels are high at the time of a stroke, then brain damage can be more severe and extensive. This occurs because when the brain is deprived of oxygen, the body breaks down glucose differently. The products of this breakdown are in and around the area of dead tissue (infarction) and are, themselves, toxic to the brain tissue. If blood circulation is restored to the area, these products will break down even further and result in an increase in the size of the infarction.
Treating diabetes can delay or prevent the onset of complications that increase the risk of stroke. Healthy eating, physical activity, and insulin via injection or an insulin pump are the basic therapies for type 1 diabetes.
Healthy eating, physical activity, and blood glucose testing are the basic management tools for type 2 diabetes. In addition, many people with type 2 diabetes require oral medication, insulin injection, or both to control their blood glucose levels.
Hardening of the Arteries (Atherosclerosis/Arteriosclerosis): Atherosclerosis and arteriosclerosis involve the buildup of deposits on the insides of the artery walls, which causes thickening and hardening (sclerosis) of the arteries. In atherosclerosis, the deposits consist of fatty substances. In arteriosclerosis, the deposits are composed largely of calcium.
The narrowing of the artery caused by the buildup of hardened plaque is called “stenosis.” The narrowing is measured as the percentage of the artery’s diameter that is blocked. For example, 70 percent stenosis means the artery is 70 percent blocked.
Atherosclerosis typically occurs in the carotid artery leading to the brain, resulting in a condition called carotid stenosis. This is a leading cause of ischemic stroke. Early warning signs of carotid stenosis include carotid bruits, which can be detected by a primary care physician during a physical exam. Carotid bruits are the noise made by the blood flowing past the blockage. The disturbed flow creates turbulence that can be heard by the physician listening to the artery with a stethoscope.
Hardening of the arteries currently cannot be cured, although the symptoms it causes can sometimes be treated. For example, a procedure called carotid endarterectomy can repair the damage caused by hardening of the carotid arteries in the neck that take blood to the brain. Prevention — reducing the risk of developing problems — is the best method. This can include quitting smoking, treating high blood pressure, exercising and restricting salt in the diet, and reducing cholesterol levels through diet and medications.
Heart Disease (Cardiovascular Disease): One in five Americans has some form of treatable cardiovascular disease, such as: heart valve disorders, heart muscle disease (cardiomyopathy), coronary artery disease, and hearth rhythm disorders in which the heart does not beat normally (arrhythmias). People with coronary heart disease or heart failure have a higher risk of stroke than those with hearts that work normally. Certain types of congenital heart defects also raise the risk of stroke.
Atrial fibrillation, a heart rhythm disorder (some patients describe it as a “fluttering” in their chest), is a common risk factor for ischemic stroke. The heart's upper chambers quiver instead of beat, which can allow blood to pool in the heart. This makes it easier for clots to form. If a clot breaks off, enters the bloodstream and lodges in an artery leading to or inside the brain, an ischemic stroke results. This serious complication of atrial fibrillation appears to occur six times more often in the elderly. And about 15 percent of strokes occur in people with atrial fibrillation.
There are several ways of treating atrial fibrillation:
- Medications are used to slow down the rapid heart rate. These may include drugs such as amiodarone, beta blockers, calcium antagonists, digoxin, disopyramide, flecainide, procainamide, propafenone, quinidine and sotalol.
- Electrical cardioversion may be used to restore normal heart rhythm with an electric shock.
- Radiofrequency ablation may also be used to restore normal heart rhythm. This involves inserting a thin, flexible catheter into an artery and threading it to the heart muscle where a burst of radiofrequency energy is delivered through it to destroy tissue that triggers abnormal electrical signals or to block abnormal electrical pathways.
- Surgery (rarely used) also can be used to disrupt electrical pathways that generate atrial fibrillation.
- An atrial pacemaker can be implanted under the skin of the chest to regulate the heart rhythm.
High Blood Pressure (Hypertension): High blood pressure (generally considered over 120/80 mm Hg) is the most common and most serious of all the controllable risk factors for stroke – particularly hemorrhagic stroke. Compared with people with controlled high blood pressure, people with uncontrolled high blood pressure are seven times more likely to have a stroke.
When your heart beats and pumps blood into your arteries, it creates pressure in them. The pressure causes your blood to flow to all parts of your body, transporting vital oxygen and nutrients. Arteries stretch when blood is pumped through them. How much they stretch depends on their health (the more muscular and elastic, the more they can stretch) and how much pressure the blood exerts.
High blood pressure puts excess stress on the heart (which has to pump harder) and damages blood vessels. If there is a weak spot in a blood vessel wall in the brain, high blood pressure could eventually cause it to rupture.
Sometimes high blood pressure is linked to other conditions, such as kidney disease, pregnancy or hormonal disorders, or caused by certain medications. The most common reasons for hypertension appear to be related to family history and influenced by diet (high salt intake or obesity) or habits such as smoking and drinking excessive amounts of alcohol.
It is common to have high blood pressure and not know it. The disease has no symptoms and is often called the “silent killer.” The only way to be certain is to have your pressure checked regularly by a health professional. The condition can be managed through a broad array of lifestyle changes (such as diet and exercise) and medications, of which there are more than 50 different types.
Transient Ischemic Attack (TIA): TIAs are "warning strokes" that produce stroke-like symptoms but no lasting damage. Recognizing and treating TIAs can reduce the risk of a major stroke.
Risk Factors We Can Prevent or Manage
Age: People of all ages can suffer stroke, but the older you are, the higher your risk. The chance of suffering a stroke more than doubles for each decade of life after age 55. It is most prevalent among the elderly because as people age, they tend to develop many of the risk factors for stroke. For example, their arteries tend to harden and become less elastic, making them more prone to rupture or blockage.
Although stroke often is considered a disease of the elderly, 25 percent occur in people younger than 65 years. In fact, every year, five out of every 200,000 children have a stroke. It can even happen in utero.
The causes in children tend to be quite different from the usual ones in adults. Children haven’t had the time to develop hardening of the arteries (atherosclerosis) or other long-term effects of hypertension, high cholesterol, diabetes, and smoking that are among the most common stroke risks in adults. Causes can vary according to a child’s age and can include:
- brain infections acquired in the uterus or during or after birth
- premature birth (for example, inadequately developed blood clotting mechanisms and immature, fragile blood vessels)
- birth defects of the heart or brain
- blood clotting disorders
- severe infections
- metabolic disorders
Gender: Men have a higher risk for stroke (1.25 times that of women), but more women die from stroke. Women account for three out of every five stroke deaths. (This may be due in part to the fact that men do not live as long as women so they are usually younger when they have their strokes and therefore are better able to survive the trauma.)
Nearly one in five women over 45 will have a stroke by age 85. Among women worldwide, stroke is the No. 2 cause of death and No. 1 cause of disability.
Ethnicity & Heredity: Stroke is more common in people whose close relatives have suffered stroke. This appears to indicate certain genetic “predispositions” within families that put them at greater risk for stroke.
African-Americans have a higher risk of death from stroke than do Caucasians. This is partly because blacks have a higher incidence of many of the risk factors for stroke. For example, high blood pressure tends to occur earlier in African-Americans and be more severe. Sickle cell disease (sickle cell anemia) — a genetic disorder primarily affecting African-Americans — is a risk factor for stroke because "sickled" red blood cells are less able to carry oxygen to the body's tissues and organs. They also tend to stick to blood vessel walls, which can block arteries to the brain.
African Americans – along with Hispanics, American Indians and Asians – appear to be at higher risk for developing type 2 diabetes.