A stroke can occur when a blood clot blocks a blood vessel carrying nutrients and oxygen to the brain, resulting in brain cell death. Doctors refer to this as an ischemic stroke.

A blood clot may cause an ischemic stroke due to obstruction in a blood vessel that transports blood to the brain, or a transient ischemic attack (TIA), which people sometimes call a mini-stroke. In a TIA, the blockage is temporary, and the clot typically dislodges or dissolves quickly.

A TIA may indicate that a person is likely to have a more severe stroke in the future. Stroke is the second leading cause of death worldwide, affecting almost 800,000 people in the United States annually.

This article explains how a blood clot causes a stroke and whether blood clots cause all strokes. It also discusses risk factors and prevention of blood clots and stroke.

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A blood clot is the formation of proteins, platelets, and cells that stick together and form a mass in the blood. The body produces blood clots to stop the bleeding after a person injures themselves, and they typically dissolve once the wound heals.

If the body produces abnormal or excessive blood clots, the blood clots may not break down as they should. These blood clots may block blood vessels, resulting in ischemic stroke or other health complications.

The main cause of ischemic stroke is blood clotting due to the narrowing and hardening of the arteries, which is called atherosclerosis. This happens when the artery walls become lined with fatty deposits made up of cholesterol, fats, and other substances. These fatty deposits harden into plaque, which can break open. If this occurs, platelets may gather around the affected areas and form blood clots.

The fatty deposits can lead to two types of blockages, which in turn lead to ischemic stroke:

  • Cerebral embolism: A cerebral embolism is a blood clot that forms somewhere in the circulatory system, usually in the heart or large arteries of the chest and neck. The most common cause is an irregular heartbeat or atrial fibrillation, which can cause a clot to form in the heart, dislodge, and travel through the bloodstream to the brain. Once the blood clot reaches a blood vessel in the brain too narrow to pass through, it obstructs blood flow and, therefore, oxygen to the brain.
  • Cerebral thrombosis: This blood clot develops at the site of fatty plaque inside the blood vessel in the brain. The blood clot obstructs the passage of blood through the blood vessel and causes an ischemic stroke.

Learn about the difference between thrombosis and embolism.

Blood clots are not the only cause of stroke. While blood vessel obstruction can lead to ischemic stroke or TIA, sudden bleeding on the brain may cause a hemorrhagic stroke.

What causes an ischemic stroke?

Blood clots cause most ischemic strokes, which account for 87% of all strokes. However, other cellular debris, such as plaque, may also break away from the arterial walls and obstruct a blood vessel in the brain, leading to an ischemic stroke.

What causes a hemorrhagic stroke?

If an artery in the brain ruptures, the blood that leaks from it can cause the brain to swell. The pressure the swelling causes can damage brain cells. A hemorrhagic stroke may occur as a result of:

There are various risk factors for blood clots, including:

  • family history of blood clots
  • smoking
  • pregnancy and giving birth
  • remaining in one position for a prolonged period, such as sitting during a long plane or car journey
  • serious injuries
  • serious surgeries, such as hip replacement
  • some medications, such as birth control pills

Health conditions that may increase a person’s risk of blood clots include:

People at high risk of developing blood clots may need blood thinning medication, such as antiplatelets or anticoagulants.

Other steps that may help prevent blood clots include:

  • stopping or avoiding smoking
  • maintaining a moderate weight
  • getting regular exercise
  • moving around as soon as possible after surgery or illness
  • moving around every few hours during long periods of sitting

Learn about treatment and home management for blood clots.

There are various risk factors for stroke, including:

  • family history of stroke
  • older age, as the risk of stroke increases after the age of 55
  • sex, as females are more likely to die from stroke
  • smoking or using tobacco
  • eating a diet high in cholesterol, trans fats, and saturated fats
  • drinking excessive alcohol
  • getting too little physical activity

The Centers for Disease Control and Prevention (CDC) notes that Black people are more likely to die from a stroke than white people. One reason for this may be inequities in healthcare.

Health conditions that may increase a person’s risk of stroke include:

Read more about the risk factors for stroke.

While a person cannot change some risk factors of stroke, such as age and family history, some lifestyle choices can help prevent stroke, including:

  • stopping or avoiding smoking
  • eating a diet high in fiber and low in saturated fats, trans fats, and cholesterol
  • getting regular physical activity
  • avoiding or limiting alcohol
  • discussing health conditions with a doctor and taking steps to control diabetes, blood pressure, cholesterol, and heart disease

Learn how to avoid a stroke after a TIA.

Blood clots are the main cause of ischemic stroke, the most common type of stroke. A blood clot can obstruct blood flow and oxygen to the brain, resulting in brain cell death. It is a medical emergency.

Other cellular matter, such as plaque, can also obstruct blood vessels and result in an ischemic stroke. Sudden bleeding in the brain can also cause a stroke, which doctors call a hemorrhagic stroke.

Risk factors for blood clots and stroke include a family history of the conditions, smoking, and various other health conditions, such as diabetes and high blood pressure.

A person may be able to help prevent blood clots and stroke by eating a diet low in saturated fats, trans fats, and cholesterol, getting regular physical activity, and taking steps to manage other health conditions.