Strokes may have a variety of causes depending on the type of stroke involved. For example, ischemic strokes are usually caused by a blood clot that restricts the flow of blood to the brain. They can also be caused by severe atherosclerosis, which can also block the passage of blood to the brain. Hemorrhagic strokes are generally caused by the bursting of an artery within the brain. This can occur when a weak spot on an artery wall expands (cerebral aneurysm) or when artery walls begin to lose elasticity, leaving them brittle, thin and prone to cracks.  

There are several risk factors associated with strokes. In general, risk factors for stroke are the same among adults of both genders and all races and ethnic backgrounds. These risk factors include:

• Age. While strokes can strike at any age, nearly three-quarters of strokes occur in people older than 65, according to the Centers for Disease Control and Prevention (CDC).
  
  
• Gender. Men have a slightly higher risk for stroke than women, but women are more likely to die from stroke. Men are more likely than women to suffer a second stroke.
  
  
• High blood pressure (hypertension). Studies have shown that people with hypertension are 4 to 6 times more likely to have a stroke than people without hypertension. Hypertension is considered an important risk factor for stroke because it usually presents no symptoms or warning signs.
  
  
  
  
• Coronary artery disease (CAD). There is a strong correlation between CAD and ischemic stroke because both are caused by the same underlying process, atherosclerosis. Atherosclerosis occurs when arteries are obstructed by plaque deposits. This may cause the arteries to rupture.
  
  
• Atrial fibrillation. This heart rhythm disorder can cause the blood to clot. If pieces of these clots break off and block an artery, a stroke can occur. Atrial fibrillation can increase a person’s risk of stroke by 4 to 6 percent, according to the National Institutes of Health (NIH). About 15 percent of patients experience this heart rhythm disorder prior to having a stroke, according to NIH.
  
  
• Diabetes. People with diabetes have two to four times the risk of stroke compared to people who do not have the illness, according to the CDC. Having diabetes also appears to worsen the outcome of a stroke in many cases. People with diabetes are more likely to have many of the risk factors for a stroke, including high blood pressure, CAD and atherosclerosis. The risk of stroke may be increased in diabetes patients who are unable to control their blood sugar levels.
  
  
• Smoking. Smoking doubles a person’s risk for ischemic stroke, according to the CDC. Smoking promotes atherosclerosis, in which plaque builds up on the walls of arteries. In addition, smoking increases the levels of certain blood clotting factors, such as fibrinogen. Nicotine also raises blood pressure, and the carbon monoxide in cigarette smoke reduces the amount of oxygen that blood can carry to the brain.
  
  
• Family history of stroke. Stroke risk increases if a person's parent, grandparent, sister or brother has had a stroke.
  
  
• Low levels of HDL (“good”) cholesterol. Poor levels of good and bad cholesterol can lead to atherosclerosis, which significantly raises the risk of stroke.
  

  

• Obesity (a body mass index of 30 or greater). People who are obese tend to have more risk factors for stroke (e.g., high blood pressure, CAD, poor cholesterol levels). While obesity is a problem among all groups of Americans, it seems to be especially prevalent among African American women.
  
  
• Lack of exercise. Not maintaining a moderate level of physical activity can lead to obesity, which increases the risk of stroke.
  
  
• Carotid artery dissection. A tear in the inner lining of the carotid artery, creating a space between the inner and outer layers that could cause a stroke if blood leaks into it.

Other possible contributors to stroke risk include:

• Sleep apnea. A condition in which a person’s breathing stops and starts many times during sleep. Interruptions in oxygen to the heart and brain can significantly increase a person’s risk of heart disease, high blood pressure and stroke.
  
  
• Atrial flutter. A type of atrial tachycardia, which is an unusually fast heart rhythm that originates in the upper chambers of the heart (atria). Atrial flutter is characterized by a very rapid but regular electrical signal in the atria, which causes a very rapid heartbeat.
  
  
• Depression. Although the exact mechanism is not clearly understood, studies continue to show an association between chronic depressive symptoms and increased risk of stroke.
  
  
• Loss of estrogen. After menopause, women’s lower estrogen levels can gradually increase their risk of stroke. Unfortunately, however, estrogen replacement therapy has also been tied to an increase in the risk of stroke. Post menopausal women should discuss with their physician about how best to reduce their risk of stroke.
  
  
• Birth control pills. While today’s low-dose oral contraceptives carry a much lower risk than the earlier pill, they still carry an increased risk of stroke for women who use them than for nonusers. The risk is more pronounced among smokers and women over the age of 40.
  
  
• Antiphospholipid syndrome. Some women who have had frequent miscarriages suffer from a condition called antiphospholipid syndrome, which causes an increased risk of stroke.

Other risk factors for stroke include alcohol or drug abuse, injuries to the head and neck and a history of strokes or heart attacks. People also face a risk of stroke during surgeries or catheter-based procedures, which have a high risk of blood clot formation.

Research is beginning to address another potential risk factor for stroke: access to health care based on race/ethnicity. Studies have shown that African Americans are less likely to receive equitable health care to white Americans. In some cases, African Americans were also seen for emergency care later in the course of their disease than whites Americans.

Children tend to have different risk factors for stroke than adults. In addition to congenital heart disease (e.g., aortic stenosis, atrial septal defect, patent ductus arteriosus), which increases the risk of stroke for adults and children alike, a wide range of diseases and conditions may raise a child's risk for stroke. These include vasospastic diseases, leukemia, sickle cell anemia, and infection with the varicella-zoster virus, which causes chicken pox.