Most blood clots in the brain are preventable. Ischemic stroke, which accounts for 87% of all strokes, happens when a clot blocks an artery supplying the brain. Over 7 million people die from stroke globally each year, making it the second leading cause of death among non-communicable diseases. The good news: the major risk factors are things you can control.
How Blood Clots Form in the Brain
The vast majority of brain clots are arterial, meaning a clot blocks one of the arteries that delivers oxygen-rich blood to brain tissue. This usually results from a buildup of fatty plaque in the artery walls (atherosclerosis), which narrows the vessel until a clot forms and cuts off blood flow. Without oxygen, brain cells begin dying within minutes.
A much rarer type, cerebral venous thrombosis, accounts for only 0.5 to 1% of strokes. Instead of blocking incoming blood, these clots form in the veins that drain blood away from the brain, causing pressure to build up inside the skull. Venous clots primarily affect younger adults and children, with a mean age of onset around 42. Women make up about 72% of cases, partly because oral contraceptives, pregnancy, and hormone replacement therapy are specific risk factors. The prevention strategies below focus mainly on arterial clots, since they cause the overwhelming majority of brain clot events.
Keep Your Blood Pressure in Check
High blood pressure is the single largest modifiable risk factor for stroke. It damages artery walls over time, making them stiffer, narrower, and more prone to clot formation. Keeping your systolic blood pressure (the top number) below 130 mm Hg significantly reduces your risk. For most people, this means regular monitoring, reducing sodium intake, staying physically active, and taking prescribed medication if lifestyle changes aren’t enough on their own.
Move Your Body Regularly
Physical activity protects your brain’s blood supply in multiple ways: it lowers blood pressure, improves cholesterol, reduces inflammation, and helps maintain a healthy weight. The American Heart Association recommends 150 to 300 minutes of moderate aerobic exercise per week, or 75 to 150 minutes of vigorous exercise.
The numbers are striking. People who participate in moderate-intensity activities can reduce their stroke likelihood by about 20%. That reduction climbs to as high as 60% with 30 to 60 minutes of daily moderate activity. Even running at a slow pace for just 5 to 10 minutes a day has been linked to a 45% lower risk of cardiovascular death compared to not running at all. You don’t need to train for a marathon. Walking briskly, cycling, swimming, or dancing all count.
Follow a Stroke-Protective Diet
What you eat directly affects blood pressure, cholesterol, and inflammation, all of which influence clot formation. A Mediterranean-style diet, rich in vegetables, fruits, whole grains, fish, nuts, and olive oil, is one of the most studied dietary patterns for stroke prevention. A meta-analysis of 15 studies found that high adherence to this diet was associated with a 32% lower stroke risk. In one large trial, participants assigned to a Mediterranean diet supplemented with extra-virgin olive oil or nuts had a 39% lower risk of stroke compared to the control group.
The DASH diet (Dietary Approaches to Stop Hypertension) offers similar benefits and shares many of the same principles. Both emphasize whole foods over processed ones and limit red meat, added sugars, and sodium. Dietary interventions overall may decrease stroke risk by roughly 19%, according to a Cochrane Review, and those numbers improve with greater adherence.
Stop Smoking
Smoking accelerates clot formation through several mechanisms at once. It increases platelet stickiness, raises levels of a clotting protein called fibrinogen, thickens the blood, and damages artery walls. The encouraging part is how quickly the body begins to recover after quitting. The increased clotting tendency reverses within days of stopping. Stroke risk then declines sharply and returns to baseline, roughly the same as a never-smoker, within about 5 years.
Manage Blood Sugar
Diabetes damages blood vessels throughout the body, including the arteries feeding the brain. Chronically elevated blood sugar promotes inflammation and accelerates plaque buildup. International guidelines recommend keeping HbA1c, a marker of average blood sugar over three months, below 7.0% for most people with type 2 diabetes. Each 1-percentage-point increase in HbA1c above target is associated with a 37% rise in stroke fatality. If you have diabetes or prediabetes, consistent blood sugar management through diet, exercise, and medication when necessary is one of the most impactful things you can do to protect against brain clots.
Understand the Role of Atrial Fibrillation
Atrial fibrillation (AFib), an irregular heart rhythm, is a major but often overlooked cause of brain clots. When the heart’s upper chambers quiver instead of contracting properly, blood can pool and form clots that travel to the brain. Doctors assess your stroke risk from AFib using a scoring system called CHA2DS2-VASc, which considers factors like age, high blood pressure, diabetes, prior stroke, heart failure, vascular disease, and sex. Each factor adds one or two points.
A score of 0 means low risk, 1 means moderate risk, and 2 or higher means high risk. For men with a score of 1 or higher, and women with a score of 2 or higher, guidelines from both the American Heart Association and European Society of Cardiology recommend blood thinners to prevent clots. If you’ve been diagnosed with AFib, this risk assessment is one of the most important conversations to have with your doctor, because anticoagulation therapy dramatically reduces stroke risk in higher-risk patients.
Rethink Daily Aspirin
For years, many people took a daily low-dose aspirin to prevent heart attacks and strokes. That advice has shifted considerably. The U.S. Preventive Services Task Force now recommends against starting aspirin for primary prevention in adults 60 and older, because the bleeding risks outweigh the benefits. For adults aged 40 to 59 with a 10-year cardiovascular risk of 10% or higher, aspirin is a personal decision to weigh with a clinician, not a routine recommendation. If you’re already taking daily aspirin, the evidence suggests considering stopping around age 75. If you’re not currently taking it, don’t start on your own.
Limit Alcohol
Heavy drinking raises blood pressure and promotes atrial fibrillation, both major stroke risk factors. Moderate consumption, generally defined as up to one drink per day for women and two for men, carries a smaller risk. But the safest approach for stroke prevention is to keep alcohol intake low or avoid it altogether, especially if you already have high blood pressure or AFib.
Recognize Warning Signs Early
Prevention also means acting fast if a clot does form. The BE-FAST tool captures over 95% of ischemic strokes and is more thorough than the older FAST acronym, which misses about 14% of cases. BE-FAST stands for:
- Balance: sudden loss of balance or coordination
- Eyes: sudden vision changes in one or both eyes
- Face: drooping on one side of the face
- Arm: weakness or numbness in one arm
- Speech: slurred or difficult speech
- Time: call emergency services immediately
The addition of balance and eye symptoms to the original checklist reduced the proportion of missed strokes from 14% down to about 4%. Every minute matters during a stroke. Brain tissue that can still be saved shrinks rapidly with each passing hour, so recognizing these signs and calling for help immediately is the last and most urgent layer of prevention.