Stroke

Description

Alternative Names

Risk Factors

New or recurrent strokes affect about 700,000 Americans every year. Although incidence of stroke has increased between 1988 and 1998, more people are surviving stroke, and the death rate from this condition fell by about 15% during that period. While age is the major risk factor, in general, people with stroke are likely to have more than one risk factor.

Age

Older Adults. People most at risk for stroke are older adults, particularly those with high blood pressure, who are sedentary, overweight, smoke, or have diabetes. Older age is also linked with higher rates of post-stroke dementia. In the older age groups, studies are mixed on the effects of stroke by gender.

Younger Adults. Younger people are not immune, however; about 28% of stroke victims are under 65. Strokes in younger people affect men and women equally.

Gender

In most age groups except older adults, stroke is more common in men than in women. However, it kills more women than men, regardless of ethnic groups. Women may have a higher risk for hemorrhagic strokes than men (although this risk is not consistent in all countries). It is not clear why women have a higher mortality rate from stroke. In one study comparing men and women with atherosclerosis (hardening of the arteries), the risk for stroke in women appeared to be higher with less blockage in the blood vessels. Another study also reported that women had a higher risk for fatal strokes after heart surgery. The arteries that lead to the brain may be more vulnerable to the effects of plaque build-up in women than in men.

Ethnicity

All minority groups, including Native Americans, Hispanics, and African Americans, face a significantly higher risk for stroke and stroke death than American Caucasians. The risk is also higher in Asian Americans, although some evidence reports a marked decline in incidence in this group over the past decades. The differences in risk among all groups diminish as people age.

The greatest disparity in risk occurs in young adults. Middle aged African Americans are two to three times more likely to experience a stroke than their Caucasian peers and four times more likely to die from one. (They also face a higher risk for death from heart disease.)

African Americans have a higher prevalence of diabetes and hypertension than other groups. However, studies suggest socioeconomic factors are important in these differences.

Poorer diets, higher stress levels, and lack of access to health care certainly play a role in the higher rates. Socioeconomic disparities may play a large role in the differences in mortality between all major American minority ethnic groups and Caucasian Americans.

All African Americans face discrimination, but women may be at particular risk for unequal treatment. (In one study in which female actors portrayed heart patients, African American women were 60% less likely to receive aggressive diagnostic tests than African American men or any Caucasians, even though they presented with similar symptoms.)

While African Americans comprise 13% of the US population, African Americans have comprised only 2% to 9% of subjects in most of the major research trials, and so knowledge about their specific risks is limited.

Geography

People in the Southeastern US have had the highest risk for stroke in the country for some years; those at particular risk live in North Carolina, South Carolina, and Georgia. This risk may be shifting westward so that high stroke rates are also occurring in the lower Mississippi valley and in Southern California. Socioeconomic differences do not fully explain these higher-risk areas.

Heart Disease and Heart Attack

Heart disease and stroke are closely tied for many reasons:

• Patients with one condition often have risk factors for the other, such as high blood pressure, atherosclerosis (hardening of the arteries), and diabetes.
• The risk of stroke is increased during surgical procedures involving the coronary arteries, including coronary bypass operations and angioplasty. Coronary bypass poses the greater risk--about 2% to 5%.
• Anti-clotting drugs used for treatment of heart disease and heart attacks slightly increase the risk for hemorrhagic stroke.
• A heart attack itself poses a high risk for stroke, which, according to a major 2002 study, is 2.5% in the first six months and 5% per year thereafter. In the study, patients with a higher risk (about 4%) for stroke within six months of a heart attack tended to be older (over age 75), African American, or to have a history of a previous stroke, atrial fibrillation, hypertension, diabetes, or peripheral artery disease. Most people at high risk have more than one of these problems.

Many of these and other heart risk factors also associated with stroke are discussed in separate discussions.

Abnormal Blood Pressure

High Blood Pressure (Hypertension). High blood pressure (known medically as hypertension) contributes to 70% of all strokes. In fact, researchers have estimated that nearly 40% of strokes could be averted by controlling blood pressure.

Two numbers are used to describe blood pressure phases and may affect stroke risk separately:

• The systolic pressure (the higher and first number) is measured as the heart contracts to pump out the blood. Evidence suggests that elevated systolic pressure poses a significant danger for heart events and stroke events when diastolic is normal, a condition called isolated systolic hypertension. The wider the spread between the systolic and diastolic measurements, the greater the danger.
• The diastolic pressure (the lower and second number) is measured as the heart relaxes to allow blood to refill the heart between beats. Abnormally higher diastolic pressure is a strong predictor of heart attack and stroke in most people with hypertension. [For more information, see the Well-Connected Report #14, High Blood Pressure.]

Hypertension is a disorder characterized by chronically high blood pressure. It must be monitored, treated and controlled by medication, lifestyle changes, or a combination of both.

Click the icon to see an image of the risks of untreated hypertension.

• Stroke from Low Blood Pressure (Hypotension). Uncommonly, blood pressure that is too low can reduce oxygen supply to the brain and cause a stroke. This can occur from a heart attack, a major bleeding episode, an overwhelming infection, or rarely, from surgical anesthesia or from overtreatment of high blood pressure.

Heart Abnormalities Causing Traveling Blood Clots (Embolisms)

Atrial Fibrillation. About one in six strokes are due to atrial fibrillation. This is a heart rhythm disorder in which the atria (the upper chambers in the heart) beat very quickly and nonrhythmically. The blood pools instead of being pumped out, increasing the risk for formation of blood clots that break loose and travel toward the brain. Atrial fibrillation, in fact, poses a six-fold increased risk for stroke and may also pose a higher risk for complications after a stroke.

Atrial fibrillation is uncommon in people under 60 years old, but about 6% of adults over 80 have this heart rhythm disorder. In this patient group, the risk for stroke may be higher or lower with the presence of other risk factors, including having heart failure, high blood pressure, diabetes, and a previous history of stroke, TIA, or rheumatic heart disease. More women than men have AF, but risk for stroke is higher in women with this condition than in men.

Patent Foramen Ovale. Patent foramen ovale (PFO) is a flap-like opening between chambers of the heart. The foramen ovale is always open during fetal development to enhance blood flow to the fetus. It then typically closes after birth when the lungs take over. However, evidence suggests that it remains open in up to 30% of adults. In such cases, blood moves backward (right to left) through this opening when pressure in the right chamber exceeds the left. Large PFOs in fact, be turn out to be a major cause of stroke, particularly in younger adults. A 2001 study suggested that stroke patients with PFO have a higher risk for a recurring stroke only if they also have atrial septal aneurysm. The process leading to blood clots and stroke in such cases are complex and not entirely clear. Treatments include anti-clotting agents and procedures for closing the opening.

Atrial Septal Aneurysm. Atrial septal aneurysm is an inborn condition in which part the atrium (one of the heart chambers) bulges out. Studies indicate that this may pose a slight risk for stroke in young people.

Note: It had been commonly believed that mitral-valve prolapse is a major cause of stroke in young people, but the connection has not been well researched. A 1999 study found no evidence that this usually mild heart abnormality has any effect on stroke.

Smoking

People who smoke a pack a day have almost two and a half times the risk for stroke as nonsmokers. Smoking increases both hemorrhagic and ischemic stroke risk. The risk for stroke may remain elevated for as long as 14 years after quitting, so the earlier one quits the better.

Diabetes and Insulin Resistance

Heart disease and stroke are the leading causes of death in people with diabetes. Diabetes is a strong risk factor for ischemic stroke, perhaps because of accompanying risk factors, such as obesity and high blood pressure. Studies have also implicated insulin resistance, which is an important disease mechanism in type 2 diabetes, as an independent factor in the development of atherosclerosis and stroke. With this condition, insulin levels are normal to high, but the body is unable to use the insulin normally to metabolize blood sugar. The body compensates by raising the level of insulin, which can, in turn, increase the risk for blood clots and reduce HDL levels (the beneficial form of cholesterol). Diabetes does not appear to increase the risk for hemorrhagic stroke. Some studies have also reported a worse outcome in patients whose blood sugar levels are high at the time of a stroke. [For more information, see the Well-Connected Report #60, Diabetes: Type 2.]

Obesity and Sedentary Lifestyles

Obesity may increase the risk for both ischemic and hemorrhagic stroke independently of other risk factors that often co-exist with excess weight, including insulin resistance and diabetes, high blood pressure, and unhealthy cholesterol level. Weight that is centered around the abdomen (the so-called apple shape) has a particularly high association with stroke, as it does for heart disease, in comparison to weight distributed around hips (pear-shape). [For more information, see the Well-Connected Report #53, Weight Control and Diet.]

Cholesterol and Other Lipids

Although an unhealthy balance of cholesterol and other lipids (fatty compounds) plays a major role in heart disease, its role in stroke is less clear. Different lipids may have different effects:

Ischemic Stroke. The effects of high total cholesterol and LDL levels on stroke are not clear. One study suggested that the risk for ischemic stroke increases when total cholesterol is above 280 mg/dl. HDL (the so-called good cholesterol) may protect against ischemic stroke (although statins have little effect on HDL).

Hemorrhagic Stroke. HDL may also reduce the risk for hemorrhagic stroke. People with overall cholesterol levels below 180 mg/dl, however, may be at risk for hemorrhagic stroke (which is bleeding in the brain), particularly if they also have high blood pressure. This is a far less common stroke, however, than ischemic stroke.

In any case, reducing cholesterol is extremely important in anyone with heart disease and abnormal lipid levels.

Genetic and Inborn Factors

Genetics may be responsible for many of the causes of stroke. Studies indicate that a family history of stroke, particularly in one's father, is a strong risk factor for stroke.

Genetics and Subarachnoid Hemorrhage. Genetic factors account for between 7% and 20% of cases of subarachnoid hemorrhage. Ruptured aneurysms that occur in such patients tend to happen at an earlier age, to be smaller, and are more apt to recur than in those without an inherited condition. A study of people who had suffered subarachnoid hemorrhages found that first-degree relatives of these stroke victims had a high lifetime risk of between 2% and 5%. Some experts recommend screening for aneurysms in people with more than one close relative who suffered a hemorrhagic stroke.

Inherited Disorders that Contribute to Stroke. Some cases of atrial fibrillation may be inherited. Genetic disorders that cause connective tissue disorders are also associated with stroke from hemorrhage; they include polycystic kidney disease, Ehlers-Danlos syndrome type IV, neurofibromatosis type 1, Marfan's syndrome, and moyamoya disease.

Specific Genetic Factors Under Investigation. Specific genetic factors are under investigation. The following are some examples:

• Inherited deficiencies in factors called protein C and S, which inhibit blood clotting, are strongly suspected of being responsible for certain cases of stroke in young adults, although one study indicated they were not significant.
• A genetic mutation in a factor V Leiden may be related to blood clotting risks.

People who have inherited a gene called apolipoprotein (Apo) E-4 may be at increased risk of stroke. This gene is also associated with Alzheimer's disease. More studies are needed.

Mental and Emotional Factors

Stress. One survey revealed that men who had a more intense response to stressful situations, such as waiting in line or problems at work, were more likely to have strokes than those who did not report such distress. In some people, prolonged or frequent mental stress causes an exaggerated increase in blood pressure. In fact, a 2001 study has linked for the first time a higher risk for stroke and elevated blood pressure during times of stress in adult Caucasian men (particularly those in lower socioeconomic groups).

Depression. Depression has also been linked to a higher risk for having a stroke and lower survival rates after one. In one 2000 study, for example, patients with severe depression had a 73% higher risk for stroke, and those with moderate depression had a 25% higher risk than average. The risk for stroke in depressed African Americans in the study was notable, 160% higher than average.

Migraine and Associated Risk Factors

Studies have found that migraine or severe headache is a risk factor for stroke in both men and women, especially before age 50. Overall, between 1.8% and 3% of ischemic strokes occur in people with a history of migraine. However, in patients under age 45, about 15% of all strokes (and 30% to 60% of strokes in young women) are associated with a history of migraines, particularly migraine with aura. Some evidence suggests that some strokes in these cases may actually be due to excessive activation of the nervous system and dehydration (e.g., from vomiting) that occurs during a severe migraine with aura. There is some weak evidence to suggest that stroke patients with a history of migraines tend to have a better outlook than other stroke patients. Interestingly, a 2001 study reported that in people who experienced migraine-related stroke, the frequency of migraines declined afterward.

The actual risk itself for migraineurs is low, however. In one study, women with migraines had a 2.7% risk of stroke, with the time of greatest risk between the ages of 45 and 65. Men with migraines had a 4.6% risk and their greatest time of risk was before age 45. In both genders, the risk diminished with age. Studies suggest specific risk factors for younger women with migraines, particularly those with auras, include taking high-estrogen oral contraceptives (OCs). (Whether progesterone-alone contraceptives carry any risk is unknown.) In migraineurs who take OCs, the risk increases with high blood pressure, smoking, or both.

Infections and Inflammation

Inflammation that occurs with various infections has been associated with stroke. A 1998 study found that patients hospitalized for stroke were three times more likely than patients without strokes to have recently been exposed to infections, usually mild ones in the respiratory tract.

Varicella Virus. Varicella zoster virus (the virus that causes chicken pox and shingles) has been associated with cerebral vasculitis, a condition in which blood vessels in the brain become inflamed. It is a very rare cause of stroke in children. The virus has also been associated with some cases of stroke in young adults.

Chlamydia Pneumonia. Some investigators suspect that some infections may produce inflammation in the arteries that can lead to stroke over time. (Similar work is underway in heart disease.) Researchers are particularly interested in Chlamydia pneumoniae, a non-bacterial organism that causes mild pneumonia in adults. Chronic infection has been linked with a higher risk for stroke and evidence of the organism has been observed in thickened inner vessel walls of the carotid arteries in some studies. Chlamydia has also been linked to heart disease.

Periodontal Disease. A number of studies now strongly support an association between periodontal disease and cardiovascular disorders. According to a major 2003 analysis, periodontal (gum) disease is associated with a 20% higher risk for ischemic stroke and heart disease. (The added risk may be even greater in adults under 65.) Recent evidence is pointing to the inflammatory response as the common element.

Peripheral Artery Disease

Peripheral artery disease (PAD) occurs when atherosclerosis affects the extremities, particularly the feet and legs. In fact, the major risk factors for heart disease and stroke are also the most important risk factors for PAD. (The occurrence of such conditions in combination with PAD often signals more severe forms of heart or circulatory disease.) [For more information see Well-Connected Report #102 Peripheral Artery Disease.]

Other Medical or Physical Conditions Associated with a Higher Risk for Stroke

A number of medical or physical conditions may contribute to the risk for stroke:

• Sleep apnea. This common disorder, in which the throat becomes obstructed during sleep, may contribute to the narrowing of the carotid artery, appearing to increase the risk for stroke three- to six-fold.
• Pregnancy. Pregnancy carries a very small risk for stroke, mostly in women with pregnancy related high blood pressure and in those with cesarean delivery. The risk appears to be higher in the postpartum (post-delivery) period, perhaps because of the sudden change in circulation and hormone levels.
• Anti-phospholipid antibodies. Nearly 40% of young people with strokes and 10% of all stroke patients have components of the immune system known as anti-phospholipid antibodies that increase the chance for blood clots.
• Sickle-cell anemia. People with sickle-cell anemia are at risk for stroke at a young age.
• Drug abuse, particularly with cocaine and increasingly methamphetamine (an amphetamine), is a major factor in the incidence of stroke in young adults.

Other Factors Associated with Stroke

Timing. Like heart attack and sudden cardiac death, stroke appears to be more common in the morning hours, perhaps due to a temporary rise in blood pressure at that time. Various studies point to a higher risk for stroke on weekends, Mondays, and holidays. The risk for hemorrhagic stroke may also be higher in the winter, particularly in older hypertensive people.

Height. Shorter people are at higher risk than taller individuals.

Homocysteine and Vitamin B Deficiencies. Abnormally high blood levels of the amino acid homocysteine, which occur with deficiencies of vitamin B6, B12, and folic acid, are strongly linked to an increased risk of coronary artery disease and stroke. Some experts believe that homocysteine is a major risk factor for stroke, second only to high blood pressure. A major 2002 study suggested that lowering homocysteine levels with folic acid would reduce the risk for heart disease by 16% and stroke by 24%.

Neck Manipulation. Some studies have reported a higher risk for stroke from injury to the carotid artery after neck manipulation by a chiropractor.

Anabolic Steroids. Steroids used for body-building increase the risk.