All types of strokes involve the interruption of blood supply to some area of a person’s brain. Both blocked and leaking blood vessels result in a lack of oxygen and nutrients in the brain cells. It takes only a few minutes after blood flow is interrupted—or even seconds—to kill millions of brain cells. 

  • Thrombotic or embolic strokes usually occur when some areas of the blood vessels are damaged by atherosclerosis—a build-up of cholesterol and other fats, combined with calcium. This leads to formation of atherosclerotic “plaques.” Atherosclerosis in these areas results in blood clots that can suddenly clog up and block already narrowed arteries. Sometimes the narrowing occurs in the carotid arteries of the neck, stopping the blood from getting to a person’s brain. In rare occasions, very low blood pressure can prevent enough blood from getting to the brain during a medical emergency, such as while being in shock.
  • Embolic strokes are often associated with an irregular or abnormal heart rhythm in one of the upper chambers of your heart (called an atrium). The abnormal rhythm is called atrial fibrillation. Atrial fibrillation may cause blood clots to form in the heart, which may travel up to the brain and cause an embolic stroke.  
  • Intracerebral hemorrhagic strokes are usually caused by uncontrolled high blood pressure (hypertension).
  • Subarachnoid hemorrhagic strokes are more likely to result from the breaking of a weak area of a blood vessel known as an aneurysm. Often, these weak areas are abnormalities that someone may have been born with.

Lifestyle Factors

A person’s likelihood of having a stroke is higher if their lifestyle is unhealthy. The following lifestyle factors increase a person’s stroke risk:

  • Obesity or being overweight
  • A diet high in saturated and trans fats and low in “good” fats
  • High salt intake
  • Alcohol abuse
  • Substance abuse (cocaine and other illegal drugs)
  • Smoking 

Medical Factors

Having certain medical conditions or diseases increases a person’s chances of having a TIA or a stroke. These conditions include: 

  • Previous stroke or TIA
  • High blood pressure (hypertension). This is the number one risk factor for stroke.
  • Atrial fibrillation
  • Diabetes
  • Family history of stroke
  • High cholesterol
  • Older age (the risk increases for people over age 55)
  • Race (stroke is more likely to cause death in African Americans)
  • Heart disease
  • Atherosclerosis
  • Peripheral artery disease (PAD). This is when plaques are present in blood vessels that carry blood to different parts of the body, especially to legs or to the brain via the carotid arteries. This can lead to reduced blood flow to these body parts.
  • Other circulation problems that are not well-controlled, such as sickle cell anemia
  • Anemia that is left untreated

Last Updated September 2020