A stroke happens when blood flow to part of the brain stops, either because a vessel is blocked by a clot or because a vessel bursts. Most strokes are built over years by high blood pressure, smoking, diabetes, high cholesterol and an irregular heartbeat. Most of those causes can be treated.
What causes a stroke?
A stroke is caused by the loss of blood supply to part of the brain. Brain tissue starts to die within minutes, which is why a stroke is an emergency and never something to watch overnight.
There are only two ways it happens. Either a vessel carrying blood into the brain is blocked, usually by a clot, or a vessel bursts and blood escapes into the tissue. Worldwide estimates put the blocked kind at about six in ten of all new strokes.
The conditions that bring a vessel to that point are familiar ones: high blood pressure, smoking, diabetes, high cholesterol and an irregular heartbeat. In a typical large blocked-vessel stroke, close to two million nerve cells are lost for every minute that treatment is delayed.
So most strokes are not caused by one bad day. They are usually the end of years of quiet damage inside vessels, often with no symptoms along the way. Worldwide, stroke is the second-leading cause of death, which makes this a common problem rather than a rare one.
Ischemic and hemorrhagic: the two brain stroke causes
Brain stroke causes sort into two groups. An ischemic stroke is a blocked vessel, so the brain beyond the blockage is starved of blood. A hemorrhagic stroke is a burst vessel, and the blood that escapes presses on the brain around it.
The clot in a blocked stroke comes from one of two places. It either builds up in the vessel wall over years and finally closes the vessel off, or it forms elsewhere, often in the heart, and travels up until it lodges in a brain vessel.
Bleeding that happens on its own, with no injury, usually comes from disease of the brain’s small vessels. That is either the damage left by years of high blood pressure, or cerebral amyloid angiopathy, a protein that collects in vessel walls in older people and makes them fragile.
The two kinds are not evenly split. Worldwide estimates put the blocked kind at about six in ten new strokes, bleeding into the brain tissue at under three in ten, and bleeding around the brain at about one in ten. Reviews that count differently put bleeding into the brain lower, at 10 to 15 in every 100 strokes.
The risk factors split too. High blood pressure is tied more tightly to the bleeding kind, while smoking, diabetes, cholesterol and heart problems are tied more tightly to the blocked kind. Neither list is exclusive, and both kinds can follow either.
A neurosurgeon is called more often for the bleeding kind, because blood inside the skull takes up room the brain does not have. That does not make a blocked stroke the lesser problem. It is just as urgent, and it is treated by a different route.
Seek care now
When to get to a hospital right away
Any of the signs below, arriving suddenly, means a hospital tonight rather than a clinic in the morning. The word that decides is sudden.
- Sudden drooping of one side of the face
- Sudden weakness or numbness in one arm or one leg
- Sudden trouble speaking, or trouble understanding what is said
- Sudden loss of vision in one or both eyes
- Sudden loss of balance, or a fall with no warning
- A sudden severe headache unlike any headache before
Balance and vision earn their place on that list. In one hospital review, checking only the face, the arms and speech would have missed a large share of strokes at the back of the brain. Adding balance and eye signs does produce more false alarms, which is the right trade when the alternative is missing a stroke.
Go to the nearest hospital that has a CT scanner. Do not wait for morning and do not drive yourself. Note the time the symptoms started, or the time the person was last seen well, because that time decides which treatments are still possible. Bring the list of maintenance medicines, any home blood pressure readings and any previous scans.
One honest exception belongs here. Weakness or confusion in an older adult that came on over days or weeks, rather than in a minute, may not be a stroke at all. It can be a chronic subdural hematoma, which can look like a stroke in an older adult, and it needs a scan rather than reassurance.
What are the main risk factors for stroke?
The main risk factors for stroke are high blood pressure first, then excess weight, raised blood sugar, air pollution and smoking. A risk factor is not the cause of any one person’s stroke. It is something that raises the odds across a whole population.
That distinction matters, because a small number of factors carry most of the burden. In a study across 32 countries, ten treatable risk factors together were associated with about 90 in every 100 of the population risk of stroke. The figure for southeast Asia was higher still, and the Philippines was one of the participating countries.
The useful way to hold all this is in two columns. The list of things that can be changed is much longer than the list that cannot, and that is the point of this post.
Which stroke risk factors can you change?
High blood pressure comes first, and by a distance. In that same 32-country study, a history of high blood pressure or a reading at or above the 140/90 threshold the study used carried about three times the odds of a stroke, and it accounted for the largest share of stroke in the population. Bleeding into the brain usually comes from small-vessel damage of exactly this kind, which is how one condition drives both the blocked and the burst stroke.
Smoking has its own section below, because readers ask about it on its own.
Diabetes roughly doubles the risk of the blocked kind of stroke and raises the bleeding kind by less. Estimates vary widely: a pooled analysis of 102 studies found about twice the risk of ischemic stroke, while the 32-country study found a much smaller effect.
Cholesterol enters as a balance rather than a single number. In the same study, an unfavourable ratio between the proteins that carry cholesterol into and out of the vessel wall went with higher odds of stroke.
Atrial fibrillation is an irregular heartbeat in which the upper chambers quiver instead of beating cleanly, so blood pools, a clot can form there, and the clot can travel to the brain. Heart causes carried about three times the odds of stroke in the 32-country study. Older long-term work found that the share of strokes explained by atrial fibrillation rises with age rather than falling.
High intake or heavy episodes of drinking carried about twice the odds of stroke compared with people who never drank or had stopped. That study did not measure whether a smaller amount is safe, so no safe amount is given here.
A salty diet is associated with about a quarter higher risk of stroke across pooled studies. Regular physical activity and a better-quality diet ran the other way, with lower odds of stroke, and a larger waist relative to the hips went with higher odds.
Can a stroke be caused by smoking?
Yes. Smoking raises the odds of a stroke by roughly two thirds, and at population level it accounts for about 12 in every 100 strokes.
That is a minority of strokes, and smoking still sits among the five leading risk factors for stroke worldwide by the amount of illness and early death it carries. Its measured effect is larger on the blocked kind than on the bleeding kind, which does not mean it spares either.
Estimates of the size differ between studies. An earlier report from the same 32-country project found a larger effect than the later one, and the more conservative figure is the one used here. What the research measures is how much the odds rise, not the precise mechanism in the vessel wall.
What is known about stopping is encouraging, and worth stating carefully. In a review restricted to people with diabetes, those who had stopped smoking sat close to people who had never smoked, while current smokers carried clearly higher risk. That is a comparison between groups, not a promise to one person, and no source here measures how long the change takes.
Which stroke risk factors can you not change?
The list that cannot be changed is the shorter one: age, family history, and having already had a stroke or a warning stroke. None of them is a reason to give up on the longer list. They are the reason to work on it harder.
Stroke becomes more common as people get older. No figure is offered here for how much the risk rises per decade, because the sources behind this post do not measure that. One age effect is measured: the share of strokes explained by an irregular heartbeat rises with age instead of falling.
Men and women both have strokes. In the 32-country study, the same handful of treatable risk factors carried most of the risk in both sexes and in every region examined.
A stroke in a parent, a brother or a sister raises your own risk modestly. The better-quality studies put it at about 1.3 times, the studies disagree with each other, and none of it means a stroke is inherited the way eye colour is.
The loudest warning anyone ever gets is a transient ischemic attack, a warning stroke whose symptoms clear completely. In a large registry of patients seen urgently by stroke specialists, most of the early risk of a full stroke landed in the first days, and the raised risk continued for years afterwards. Clinics that see these patients within a day have reported a lower early risk than older studies found, which is one more reason to be seen urgently.
Why do younger adults have strokes?
Younger adults have strokes for the same reasons older adults do, plus a few that belong to them. Stroke is not only a disease of the elderly: worldwide, both the number of people living with stroke and the rate of new strokes rose among people under 70 over three decades, even while age-adjusted rates fell.
In a registry of 26 hospitals in Argentina, adults aged 18 to 50 made up about eight in every 100 ischemic strokes. The commonest risk factors in that group were high blood pressure, smoking and obesity, which is to say the ordinary ones, arriving early.
Two things are different in a younger patient. In about half of that Argentine group no cause was found at first, and among the less usual causes that were identified, a tear in an artery wall was the most frequent. Some cases went with a patent foramen ovale, a small flap between the two sides of the heart that never closed.
On the bleeding side, a younger patient is also checked for an aneurysm, a weak bulge in a vessel wall, and for a tangle of abnormal vessels. Those are looked for rather than assumed, and no figure is given here for how often they are found.
What raises stroke risk in the Philippines?
High blood pressure is the local answer, and the difficulty here is not that it is rare but that it goes untreated. A review of Philippine data found about a quarter of Filipino adults living with high blood pressure, almost half of them unaware of it, and only 27 in every 100 with it under control. In that same review, stroke was the commonest complication recorded among Filipino patients with high blood pressure.
Everyday diet is the second thread. A Philippine modelling study estimated that a tax on packaged foods high in salt or sugar, by cutting how much of them people eat, would avert thousands of blocked strokes over 20 years. That is a projection under a policy that has not been implemented, and it is quoted here only for the scale it implies.
One exposure runs against the global trend. In modelled estimates, the stroke burden attributed to smoke from solid cooking fuel indoors fell in most countries over three decades while rising in the Philippines.
Forecasts for Asia keep raised blood pressure as the leading contributor to cardiovascular death in the coming decades, with stroke one of the two largest drivers. What this post cannot give you is a dependable national figure for how many Filipinos have a stroke each year, or where stroke ranks among causes of death here. No such figure was found for this post, and a global number is not a substitute for one.
What to do now
How do you lower your risk of a stroke?
Start with the blood pressure, because that is where the evidence is strongest. Across 123 randomised trials, every 10 mmHg fall in the upper blood pressure number went with about a quarter lower risk of stroke. That is an average across trial populations rather than a promise to any one person.
The rest is ordinary, unglamorous follow-through.
- Know your own blood pressure number, not only that it was called a little high.
- Take maintenance medicine the way it was prescribed, not only on the days your head aches.
- Keep the follow-up, and bring your home readings to it.
- Ask whether your heart rhythm has ever been checked for an irregular beat.
- Ask what your blood sugar and cholesterol were, and what the plan is if a reading is high.
For almost all of this, the first doctor is not a surgeon. If you are unsure whether to see a neurologist or a neurosurgeon, start with the physician who already handles your blood pressure and let them decide what needs a specialist.
What a referring physician should work up
The first job is the clock and the scan, not the cause. Establish the time of onset or the time last seen well, and separate ischemic from hemorrhagic on non-contrast CT before anything else, because the two are treated in opposite directions and imaging is the only thing that distinguishes them. Blood pressure, capillary glucose and cardiac rhythm follow immediately.
Intracerebral hemorrhage is a minority of strokes yet carries a disproportionate share of stroke deaths and disability. Cases that usually need a neurosurgeon include blood occupying space, blood in the ventricles with hydrocephalus, a bleed or large infarct in the cerebellum, a pattern that raises suspicion of an aneurysm or vascular malformation, and a large infarct with swelling. When in doubt, discuss the scan.
A transient ischemic attack is not an outpatient slot for next month. In a registry of patients assessed urgently, risk was front-loaded into the first days, and multiple infarcts on imaging, large-artery disease, or a high ABCD2 score, a short bedside risk score, each more than doubled it.
A young or otherwise unexplained stroke prompts a search for arterial dissection, a clotting disorder and a cardiac source, including a patent foramen ovale. On the bleeding side, secondary prevention rests on sustained blood pressure control and on getting antithrombotic therapy right, which are decisions for the treating team.
Send the time of onset, the medication list including any blood thinner, the blood pressure readings, and the images themselves rather than only a report. It also helps the family to know what to bring to a first appointment.
Frequently asked questions
Can stress cause a stroke?
Stress and low mood, which this research groups together as psychosocial factors, were associated with about twice the odds of stroke in the 32-country study. Because people were asked to recall their stress after the stroke, that design cannot show stress caused it, and treating stress as the whole explanation hides the treatable causes.
Can a stroke happen while you sleep?
Yes, and people do wake with the symptoms already present. Even when nobody knows what time it began, imaging can sometimes still show that emergency clot-dissolving treatment is possible, so waking with symptoms is a reason to go in at once rather than to assume the chance has passed.
Does high blood pressure always cause symptoms first?
No. Almost half of Filipinos with high blood pressure do not know they have it, which means it usually gives no warning. The only way to know the number is to have it measured.
Is a mini-stroke serious if the symptoms went away?
Yes. Symptoms that clear completely still carry a real risk of a full stroke in the days that follow, and in a registry of urgently assessed patients most of the early risk fell inside the first week.
Can a stroke be inherited?
Family history raises risk somewhat, by about 1.3 times in the more reliable studies, and the evidence is mixed. A stroke in the family is a reason to have your own blood pressure, sugar and cholesterol checked, not a verdict about your future.
Can a fall or a blow to the head cause a stroke?
A head injury and a stroke are different problems with different clocks. A blow to the head can cause bleeding around or inside the brain rather than what is usually meant by a stroke, and an injury to the neck can rarely tear an artery. Weakness appearing days or weeks after a head injury after a fall in an older adult is a reason to be seen rather than to wait.
See sources
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