New or recurrent strokes affect about 600,000 people 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
Major studies have reported that ischemic strokes are more deadly in women than in men, regardless of ethnic groups. (A 2000 Canadian analysis of nearly 45,000 patient records, however, reported that among elderly stroke sufferers, women had a slight edge in survival a year after a stroke even though older men were more aggressively treated.) 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.) Reasons for both of these risks may include the following:

 
• African Americans have a higher prevalence of diabetes and hypertension than other groups.  
• Poorer diets, higher stress levels, and lack of access to health care certainly play a role. It should be that 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.  
• One study found that African Americans produce less nitric oxide in response to stress; this substance is critical for opening blood vessels and increasing blood flow.

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.

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.

Atrial Fibrillation
About one in six strokes is due to atrial fibrillation. This is a heart rhythm disorder in which the atria (the upper chambers in the heart) beat very quickly and irrhythmically. 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. [ See Box Atrial Fibrillation and Its Treatments.]

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
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 (hyperinsulinemia), 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.

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).

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. HDL (the so-called good cholesterol) may be the most important lipid for preventing ischemic stroke. The effects of high total cholesterol and LDL levels on stroke are less clear. One study suggested that the risk for ischemic stroke increases when total cholesterol is above 280 mg/dl.

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.

Alcohol, Coffee, and Drug Abuse
Alcohol. Heavy alcohol use, particularly a recent history of drinking, is associated with a higher risk of both ischemic and Hemorrhagic stroke. Studies have indicated, however, that mild to moderate alcohol use (one to seven drinks a week) is associated with a significantly lower risk for ischemic stroke, although not Hemorrhagic stroke.

Coffee. Studies suggest that drinking three or more cups of coffee a day could increase the risk of stroke in older men with hypertension. Coffee does not appear to pose a danger for men with normal blood pressure.

Drug Abuse. Drug abuse, particularly with cocaine and increasingly methamphetamine (an amphetamine), is a major factor in the incidence of stroke in young adults. Steroids used for body-building also increase the risk.

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, Marfans 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.

Heart Disease and its Treatments
Heart disease and stroke are closely tied for many reasons:

 
• They often have common risk factors, including 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, angioplasty, and coronary atherectomy.  
• Thrombolytic (clot-busting) and other anti-clotting drugs used for treatment of heart attacks also slightly increase the risk for Hemorrhagic stroke.  
• A heart attack itself increases the risk for a stroke. Those at higher risk are older people and patients who also have congestive heart failure.

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.

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, 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. In fact, migraine is associated with about 19% of all strokes. It should be pointed out that many people have migraines, and their risk is still low, 2.7% for women and 4.6% for men, according to one study. Women in the study were at greatest risk between ages 45 and 65 and men before age 45. In both genders, the risk diminished with age.

Oral contraceptives add to the risk for stroke in young women with migraines, but only in those who also have auras. Smoking intensifies their risk.

Taking decongestants may also increase the risk for stroke in people with migraines.

Infections
Reports have indicated for some time that certain bacteria and viruses may play a role in atherosclerosis and heart disease, generally by provoking an inflammatory response in the arteries. Similar mechanisms may be at work with stroke. Some evidence linking infections with stroke is as follows.

Lung Infections. In two 2000 studies, chronic infection with Chlamydia pneumoniae, a non-bacterial organism that causes mild pneumonia in adults, was linked with a higher risk for stroke. One of the studies reported a thickening of the inner vessel walls of the carotid arteries in patients who carried the organism. Chlamydia has also been linked to heart disease.

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.

Periodontal Disease. Chronic periodontal (gum) disease has been associated with an increased risk for ischemic stroke and heart disease. The bacteria that cause periodontitis may stimulate inflammatory factors that cause blood clots and other proteins that contribute to this higher risk. On the other hand, gum disease may simply be a common risk factor among other known risk factors for stroke, including being poor, African American, older, and overweight.

Varicella Zoster 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.

Other Medical or Physical Conditions
A number of medical or physical conditions may contribute to the risk for stroke:

 
• Sleep apnea, which may contribute to the narrowing of the carotid artery, appears to increase the risk for stroke three- to six-fold.  
• 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.  
• 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.  
• People with sickle-cell anemia are at risk for stroke at a young age.

Medications
Over-the-counter decongestants contain ingredients that increase the risk of stroke, particularly in people with other risk factors or who have Raynaud’s phenomenon. One study reported a possible increased risk for stroke in older women who regularly took aspirin; more research is needed to determine if there is any causal relationship.

Neck Manipulation with Chiropractic Therapy
Some studies have reported a higher risk for stroke from injury to the carotid artery after neck manipulation by a chiropractor. 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. Others believe it may simply be a chemical bystander, which increases in the presence of other risk factors.