Stroke happens when blood flow to part of the brain is blocked or when a blood vessel in the brain bursts. The major causes fall into two categories: medical conditions that damage blood vessels over time and lifestyle behaviors that accelerate that damage. Here are the 10 most significant causes, starting with the ones that carry the greatest risk.
1. High Blood Pressure
High blood pressure is the single largest contributor to stroke risk. It damages artery walls throughout the body, including the vessels that supply the brain. Over time, that constant force promotes the buildup of fatty plaques inside arteries, which can block blood flow and cause an ischemic stroke. High blood pressure also weakens smaller arteries deep in the brain, making them prone to rupture and causing a hemorrhagic (bleeding) stroke. Roughly half of all strokes are attributed to uncontrolled blood pressure.
2. Heart Disease and Irregular Heart Rhythm
A heart condition called atrial fibrillation, where the upper chambers of the heart quiver instead of contracting normally, is one of the most direct paths to stroke. When the heart doesn’t pump efficiently, blood pools in the left atrium and can form clots. If a clot breaks free and travels to the brain, it blocks an artery and triggers a stroke. The sluggish blood flow in atrial fibrillation also activates clotting factors and platelets, creating what researchers describe as a prothrombotic state, meaning the blood itself becomes stickier and more clot-prone. Other forms of heart disease, including heart failure and valve problems, raise stroke risk through similar mechanisms.
3. High Cholesterol
Excess LDL cholesterol infiltrates damaged spots in artery walls, triggering a chain reaction. Immune cells rush to the site and absorb the cholesterol, becoming bloated “foam cells” that accumulate into fatty plaques. Over months and years, those plaques harden with calcium and narrow the artery. Cholesterol crystals within the plaque also trigger inflammation, which can destabilize the plaque and cause it to rupture. When that happens in a carotid artery (the major vessel running up each side of the neck), the debris can travel directly to the brain and cause a stroke.
4. Diabetes
People with diabetes face roughly 1.5 to 2 times the stroke risk of people without it, and that risk climbs the longer someone has the disease. Chronically elevated blood sugar damages the inner lining of blood vessels, accelerates plaque formation, and promotes inflammation. Diabetes also tends to travel with other stroke risk factors like high blood pressure, high cholesterol, and obesity, compounding the danger. Both type 1 and type 2 diabetes increase risk, though type 2 carries a slightly higher hazard ratio at about 1.76 compared to 1.50 for type 1.
5. Obesity
Carrying excess weight raises stroke risk both directly and indirectly. Fat tissue, especially around the midsection, releases inflammatory signals that damage blood vessels. It also drives up blood pressure, blood sugar, and cholesterol. A large cohort study found that people who were both overweight and metabolically unhealthy (meaning they had at least one abnormal marker like high blood pressure or elevated blood sugar) had roughly three times the risk of ischemic stroke compared to people at a healthy weight with normal metabolic markers. Even people at a normal weight faced more than double the stroke risk if their metabolic health was poor, which underscores that the metabolic consequences of excess weight matter as much as the weight itself.
6. Smoking
Tobacco smoke damages the lining of blood vessels, makes blood more likely to clot, and raises blood pressure. Someone who smokes 20 cigarettes a day is six times more likely to have a stroke than a nonsmoker. The good news: quitting reverses much of the damage. After five years without cigarettes, your stroke risk drops back to the same level as someone who never smoked. Few interventions offer that kind of return on a single behavior change.
7. Physical Inactivity
A sedentary lifestyle sets the stage for nearly every other risk factor on this list. Without regular movement, blood pressure creeps up, blood sugar regulation worsens, cholesterol ratios shift in the wrong direction, and weight tends to climb. Regular physical activity, even moderate exercise like brisk walking, lowers stroke risk by improving all of these markers simultaneously. Current guidelines recommend at least 150 minutes of moderate activity per week.
8. Heavy Alcohol Use
The relationship between alcohol and stroke follows a J-shaped curve. A meta-analysis of 27 studies covering more than 1.4 million people found that light drinking was associated with a 15% lower risk of stroke and a 33% lower risk of dying from one. Heavy drinking, on the other hand, increased total stroke risk by about 20%. Alcohol in large amounts raises blood pressure, increases triglycerides (a type of blood fat that hardens arteries), and can trigger atrial fibrillation. The threshold between “light” and “heavy” matters, and for most adults, more than two drinks per day consistently pushes into the harmful range.
9. Poor Diet and Excess Sodium
Diets high in saturated fat, trans fat, and cholesterol directly feed the plaque-building process in arteries. But sodium deserves special attention. Excess salt raises blood pressure, and most people consume far more than they realize. The American Heart Association recommends no more than 1,500 milligrams of sodium per day for ideal cardiovascular health. In one study of a diverse urban population, 88% of participants exceeded that threshold. For context, a single fast-food meal can contain 1,500 mg or more. Reducing sodium intake is one of the most accessible ways to lower blood pressure without medication.
10. Age and Family History
Some stroke risk factors can’t be changed. Age is the most powerful non-modifiable risk factor: your chance of having a stroke doubles with every decade after age 55. A family history of stroke also raises your risk, likely through a combination of shared genetics and shared lifestyle habits. Men have a higher stroke incidence at younger ages, while women face higher lifetime risk partly because they tend to live longer. Black Americans and Hispanic Americans also face elevated stroke rates compared to white Americans, driven by a combination of genetic predisposition, higher rates of hypertension and diabetes, and disparities in healthcare access.
How These Causes Overlap
These 10 causes rarely act alone. High blood pressure accelerates the damage from high cholesterol. Diabetes worsens the effects of obesity. Smoking compounds nearly everything. This clustering is why a single stroke often has multiple contributing factors, and why addressing even two or three of these risks can dramatically lower your overall odds. The modifiable causes (the first nine on this list) account for roughly 90% of all stroke risk, which means most strokes are, in principle, preventable.