Causes and Risk Factors of Stroke

The causes and risk factors for stroke are well understood. A stroke, or the event that occurs when blood flow is interrupted or reduced, is often related to an additional condition, such as diabetes, hypertension, or infection. While a stroke may feel sudden, the reality is there are often risk factors at play for years prior to the event.

Most people who experience a stroke have more than one predisposing factor, be it obesity, a smoking habit, a sedentary lifestyle, or certain genetic traits. While you can't control your genetics, you can take control of the lifestyle factors that may be increasing your risk.

Common Causes and Risk Factors

There are three primary types of stroke: a blocked artery (ischemic stroke), leaking or bursting of a blood vessel (hemorrhagic stroke), or a mini-stroke that serves as a warning sign of a future stroke (transient ischemic attack [TIA]). In some people, disruption of blood flow is temporary and does not create lasting complications. In others, prolonged disruption of blood flow causes cell and brain death—leading to long-term complications.

Specific causes and risk factors for all forms of stroke include:

Coronary Artery Disease

Coronary artery disease (CAD) is when blood vessels of the heart become damaged. Patients with CAD have a greater risk of strokes compared to patients with a normal heart.

Intracranial Disease

Intracranial disease is a condition in which the blood vessels that deliver blood to the brain are damaged, narrow, or irregular, usually due to hypertension, diabetes, or high cholesterol.

The blood vessels in the neck are carotid arteries. If they are narrow or irregular, they can form blood clots that may travel to and lodge in the blood vessels of the brain. There are a number of interventional procedures that can repair the carotid arteries.

Heart Failure

After a heart attack or as a result of excess strain on the heart, the heart muscle becomes weakened, making it difficult to pump blood efficiently. Reduction in the blood supply to the brain can lead to a stroke.

Brain Aneurysm

A brain aneurysm is an abnormally shaped blood vessel with an outpouching, usually present from birth. It may rupture as a result of extreme blood pressure fluctuation or severe illness. If you have been diagnosed with a brain aneurysm, you may or may not be a candidate for aneurysm repair, depending on the location of your aneurysm and your overall health.

Irregular Heartbeat

An irregular heartbeat, or arrhythmia, can contribute to the formation of blood clots. These blood clots may travel to the brain and get trapped in small blood vessels, resulting in ischemic stroke.

Often, blood thinners are recommended to reduce the risk of stroke-related to an irregular heartbeat. And new at-home tools have emerged that make it easier to detect the frequency of heart rhythm irregularities throughout the day.

Congenital Heart Defects

Heart defects that are present at birth can cause a wide variety of problems, including stroke. Heart defects can include misplaced blood vessels, leaking of blood from one region of the heart to another, and other anatomical problems. Most heart defects can be detected and safely repaired at a very young age.

Heart Valve Disease

Valve disease can be congenital (present at birth) or it may develop later in life. It may also cause changes in the blood flow throughout the body, increasing the risk of blood clot formation and potentially leading to ischemic stroke.

Arteriovenous Malformation

Arteriovenous malformation (AVM) is a blood vessel abnormality that, when ruptured, causes a hemorrhagic stroke. Sometimes, AVMs can also cause neurologic deficits by “stealing” blood flow from the surrounding brain tissue.

Heart Infection or Inflammation

Inflammation and infection of the heart are uncommon, but they can cause heart failure, abnormal blood rhythms, as well as blood clots that may affect the brain.

High Blood Pressure

High blood pressure, or hypertension, causes a slowly progressive disease of blood vessels throughout the body, including the heart, the brain, and the carotid arteries. The diseased blood vessels are likely to form clots or trap clots traveling throughout the body, leading to ischemic strokes. These conditions are all likely to develop gradually over the years if high blood pressure goes untreated.

Hypertension can also contribute to the rupture of defective, abnormally shaped blood vessels, causing hemorrhagic strokes. The latest guidelines for blood pressure management recommends keeping blood pressure below 120 mmHg over 80 mmHg.

Patients with blood pressures of 120 to 129 mmHg over 80 mmHg should be treated with lifestyle changes and re-evaluated in three to six months. In patients with blood pressure that is higher than 130 mmHg over 80 mmHg, the American Heart Association recommends treating with medication.

High Cholesterol

High cholesterol, like hypertension and diabetes, can damage the arteries of the heart, carotid arteries, and brain. Cholesterol has a tendency to build up and cause stickiness within the blood vessels. This increases the chance of a blood clot getting lodged in a blood vessel and interrupting blood supply to the brain.

In healthy adults, total cholesterol should be between 125 mg/dL and 200 mg/dL. Non-HDL cholesterol should be less than 130 mg/dL, LDL should be less than 100 mg/dL, and HDL should be 50 mg/dL or higher.

Blood Clotting Disorders

Conditions that affect the ability of blood to clot—either too much or too little—can lead to stroke. In bleeding disorders, such as hemophilia, the inability to form a proper blood clot leads to excessive and prolonged bleeding. Although a brain bleed is rarely associated with bleeding disorders, it can lead to a hemorrhagic stroke if it occurs.

Blood clotting disorders, on the other hand, can lead to an ischemic stroke. People with clotting disorders are predisposed to the formation of blood clots, which can travel through the body and lodge in the brain, cutting off the blood supply.

Sickle Cell Anemia

Sickle cell anemia is a genetic disorder of the red blood cells. Those abnormal cells are rigid and can stick to the walls of the cerebral blood vessels causing a stroke.

Diabetes

Diabetes is a condition that makes it difficult for the body to maintain a normal blood sugar level. When someone with unmanaged diabetes has recurrently high blood glucose levels, the resulting metabolic changes in the body can damage arteries, causing intracranial disease, carotid artery disease, and other diseases of the arteries of the heart. All this substantially increases the chance of having a stroke.

Pregnancy

For some women, pregnancy can increase the risk of blood clotting. There is a mildly increased risk of stroke during pregnancy. It is typically associated with an underlying blood clotting disorder or an inflammatory condition.

Autoimmune Disease

Some autoimmune disorders can increase the risk of stroke by predisposing you to the development of blood vessel disease or the formation of blood clots. If you have been diagnosed with an autoimmune disease such as lupus, there is a mildly increased risk of stroke and other blood clotting events.

Severe Infections

Infections can predispose the formation of blood clots, dehydration, or heart failure. The link between infections and stroke is believed to be related to an increase in inflammation that can make a stroke more likely. In fact, even poor dental health, which causes mild oral infections, is linked to stroke.

HIV

HIV and AIDs can increase the risk of infection, inflammation, and cancer—all of which raise your stroke risk. There has been an observed increase in the incidence of stroke among people with HIV and AIDS.

Cancer

Cancer can increase the chance of stroke and can also increase the risk of infection, inflammation, and blood clotting problems—all factors that can lead to a stroke.

Your Stroke History

A person who has already had a stroke is at an increased risk of having another stroke. In fact, of the 800,000 strokes that occur in the United States each year, almost 25% are recurrent strokes.

If you have had a stroke, talk with your doctor about prevention strategies, which may include anti-platelet medications along with diet and exercise changes.

A transient ischemic attack (TIA), or mini-stroke, is a temporary and brief disruption of blood flow in the brain. A TIA is the most predictive stroke risk factor and a warning sign that you need to get a thorough health evaluation.

Non-Modifiable Risk Factors

While you have some control over certain risk factors for stroke, there are some factors for stroke that you cannot influence.

Age

Although a stroke can occur at any age, your risk of stroke increases as you grow older. From age 55 and up, your risk of stroke doubles every 10 years, and three-quarters of all strokes occur in people over the age of 65. 

Sex

Women are more likely than men to have a stroke and to die from it. Factors that increase the female odds of having a stroke include pregnancy, hormonal birth control, and longevity. In addition, women have higher rates of anxiety and depression, both of which can increase stroke risk. 

Race

Race and ethnicity also play a role in stroke risk. Whites and Asians have the lowest rates of stroke, while Blacks, Hispanics, American Indians, and Alaska Natives are at increased risk. In fact, an African American is nearly twice as likely to have a stroke as a white person of the same age and gender .

Genetics

If you have family members who have had a stroke, you may be at an increased risk due to similar lifestyle habits or hereditary factors. Be sure to tell your doctor if you have a family history of stroke, as that will guide the medical tests that they order for you.

Lifestyle Risk Factors

Certain habits and lifestyle choices can increase the risk of stroke. These are typically modifiable, meaning you have the power to reduce your risk by engaging in healthier behaviors.

Obesity

Science shows that a BMI over 30 is linked to high stroke risk. While it is known that high cholesterol, hypertension, and diabetes—which all contribute to stroke—are associated with obesity, research shows that obesity is an independent stroke risk factor.

This means that obese people are more likely to have a stroke when compared to non-obese individuals who have comparable blood pressure, cholesterol, and blood sugar. Interestingly, the most consistently documented benefit of weight loss surgery is a decreased risk of stroke.

Sedentary Lifestyle

To some, a lack of activity is a surprising cause of stroke. Yet, research consistently shows that inactivity causes stroke independently of obesity, high cholesterol, and hypertension.

It has also been proven that a moderate amount of exercise is strongly associated with stroke prevention.

Hormonal Medication Use

Taking oral contraceptives can slightly increase the chance of blood clot formation. The risk is more prevalent among smokers who use oral contraceptives.

In addition, hormonal replacement therapy has been associated with an increased stroke risk. However, there is conflicting data among a few studies showing no or decreased risk.

Stress and Mood

Long-term anxiety and agitation alter hormones in your body, contributing to hypertension and heart disease. In fact, post-traumatic stress disorder (PTSD) is associated with an increased chance of having a stroke, even years after the initial source of trauma has ceased.

Other stressful lifestyle factors, including long work hours, shift work, and family upheaval, are also strongly correlated with an increased chance of having a stroke.

Stress is the feeling most significantly associated with an increased stroke risk due to its effect on blood flow, blood pressure, and hormones throughout the body. In addition, some studies have suggested a potential association between mood disorders and strokes.

Smoking

Smoking is one of the most preventable causes of stroke. The chemicals in cigarette smoke are well known to be toxic to the lungs. But smoking also injures the inner lining of blood vessels throughout the body, making them jagged, stiff, and narrow. This makes it likely for blood clots to form and get stuck inside the arteries.

Smoking contributes to heart disease, intracranial artery disease, and carotid artery disease.

Drug Use

A variety of different drugs commonly abused are known to cause a stroke. Some drugs cause stroke during use, while others produce gradual physical damage to the body, causing a stroke after multiple uses.

Cocaine, for example, induces sudden stroke due to its tendency to cause blood vessels to spasm abruptly, blocking blood flow to the heart or brain. Repeated use of methamphetamine, on the other hand, produces long-term damage that raises the likelihood of stroke.

Chronic, heavy alcohol use has also been connected with stroke.

A Word From Verywell

Familiarizing yourself with the causes of stroke can be the best protection you have in the long-term to decrease and avoid risk. Many stroke causes overlap with and contribute to one another. That means that if you tackle one cause or risk factor of stroke, you will simultaneously minimize one or more of the others. For example, if you exercise to ward off stroke, it will also lend itself to the prevention of both hypertension and obesity.