Causes and Risk Factors of Stroke

A stroke can come as a shock and may feel like an unforgiving, arbitrary attack on your health and well-being. It happens suddenly and can potentially have serious and damaging repercussions.

But while the visible aspects of a stroke certainly strike abruptly, behind the scenes a stroke is caused by any number of factors that slowly build over years. The good news is that the causes of stroke are well understood.

Most people who experience a stroke have more than one predisposing factor. There is also a good deal of overlap among stroke causes, as some of the causes of stroke also lead to other conditions that ultimately influence stroke risk, resulting in a vicious cycle. Most of the causes of stroke, however, are preventable or at least controllable.

A stroke occurs when there is an interruption of blood flow to a region of the brain causing brain damage. This can cause diminished physical function, impaired thinking skills, or both, and the level to which this occurs varies depending on what part of the brain is injured and the extent of the damage.

Infections, pregnancy and lifestyle factors, such as obesity, smoking, and leading a sedentary lifestyle can also increase your stroke risk. Here's a closer look at common risk factors:

Transient Ischemic Attacks

A transient ischemic attack (TIA) is a reversible stroke, often referred to as a mini-stroke. Most people who experience a TIA go on to experience a stroke if the underlying risk factors are left untreated.​

A TIA is the most predictive stroke risk factor and is a warning sign that you need to get a thorough health evaluation. Typically, a TIA occurs due to one or more of the same risk factors that cause 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, cerebrovascular disease, carotid artery disease, and other diseases of the arteries of the heart. All this substantially increases the chance of having a stroke.

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 mm Hg over 80 mm Hg.

Elevated blood pressure (120 to 129 mm Hg over 80 mm Hg) should be treated with lifestyle changes and re-evaluated in three to six months. In patients with blood pressure that is higher than 130 mm Hg over 80 mm Hg, 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.

Cerebrovascular Disease

Cerebrovascular disease is a condition in which the blood vessels that deliver blood to the brain are damaged, narrow, or irregular. This can potentially lead to a stroke if left untreated.

Coronary Artery Disease

Coronary artery disease (CAD) is when blood vessels of the heart become damaged. The carotid arteries are the two largest and most important arteries that route blood from the heart to the brain. They can become narrow, stiff, and full of dangerous debris as a result of diseases such as hypertension, diabetes, and high fat and cholesterol levels. This can cause the blood supply to the brain to become compromised or, in severe situations, completely blocked.

Another way that carotid artery disease causes stroke is when the debris that builds up inside the carotid arteries becomes dislodged and travels to the brain, obstructing a cerebral vessel and causing a stroke. Surgery can help repair carotid artery disease and reduce the risk of stroke.

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, recently, new at-home tools have emerged which make it easier to detect the frequency of heart rhythm irregularities throughout the day.

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.

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.

Carotid Artery Disease

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.

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 Infection or Inflammation

Inflammation and infection of the heart are uncommon, but they can cause blood clots, heart failure, heart attack, and further infection or inflammation that may affect the brain.

Bleeding Disorders

Bleeding disorders are a group of diseases that have the inability to form a proper blood clot in common. This leads to excessive and prolonged bleeding in any part of the body, including the brain, after any type of injury. The bleeding can also occur spontaneously.

Blood Clotting Disorders

When blood clotting is abnormal, it can predispose the formation of blood clots. In turn, blood clots form in the blood vessels and travel and lodge in the brain or elsewhere in the body.

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.

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, psoriasis or alopecia areata, 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.

Brain Aneurysm

A brain aneurysm is an abnormally shaped blood vessel with an outpunching, 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. Find out more about brain aneurysm prognosis.

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.

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.

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 he/she orders for you.

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.

Hormonal Medications

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 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 emotion most significantly associated with an increased stroke risk due to its effect on blood flow, blood pressure, and hormones throughout the body. However, mood fluctuations, including depression and anxiety, are also associated with stroke.

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 most people do not realize that smoking 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

There are a number of well-known causes of stroke. Most of these risk factors are due to mechanisms that are well understood and that can prepare us to take preventive measures.

The majority of the causes of stroke overlap with each other and contribute to each other. That means that if you tackle one, you will simultaneously minimize one or more of the other causes of stroke. For example, taking diabetes medication to control blood glucose levels can, in turn, affect weight management, hormone levels, and other factors that often contribute to heart disease and stroke. Similarly, if you exercise to ward off stroke, it will also lend itself to the prevention of both hypertension and obesity.

Familiarizing yourself with the causes of stroke can be the best protection you have in the long-term to decrease and avoid risk.