How to prevent a stroke: the risk factors within your control

A parent has a stroke. Or a colleague your own age does, out of nowhere. The question arrives fast, and it is hard to shake: could that be me, and is there anything I can actually do about it?

Type "how to prevent a stroke" into a search bar and you get the same checklist everyone gets. Eat well, move more, stop smoking. All true, all worth doing, and none of it tells you what matters most for you.

The honest answer is more useful, and more reassuring. No one can promise you will never have a stroke. What you can do is shift the odds a long way in your favour, especially if you start early and work on the right things. That is what this piece is about: the risk factors you can understand, measure and act on, and how to tell which ones deserve your attention.

What "preventing a stroke" actually means

A stroke is what happens when part of the brain is cut off from oxygen. There are two ways that happens. In an ischaemic stroke, a clot lodges in an artery and closes off the blood flow behind it. In a haemorrhagic stroke, a blood vessel ruptures, and the bleed damages the surrounding tissue. Two different events, one shared result: brain tissue starved of oxygen. It does harm quickly, because nerve cells are metabolically busy and depend on a constant oxygen supply to work.

Some of what drives stroke risk cannot be changed. Age is the obvious one. So are certain inherited factors, and a family history of stroke. But the factors that carry much of the risk are a shorter list than most people expect, and they can be influenced:

• blood pressure

• insulin sensitivity

• blood lipids, particularly ApoB

• clotting factors

That is where the reassurance sits. The mechanisms behind stroke, especially the ischaemic kind, are well understood, and much of the risk lives in factors you can measure and move. The large INTERSTROKE study associated a set of modifiable risk factors with the large majority of strokes across 32 countries (O'Donnell et al., Lancet, 2016). Prevention here does not mean removing risk entirely. It means lowering it by acting on what is driving it.

And if stroke runs in your family? You are far from powerless. A family history raises your starting point, it does not remove the levers. Most of the mechanisms behind inherited risk can be measured directly and the controllable ones can be controlled. Even where an inherited marker cannot be lowered, keeping everything around it in good order, blood pressure in a healthy range, good insulin sensitivity, a low ApoB, not smoking, can reduce your overall risk.

The risk factors you can measure and act on

These factors compound, and they feed into each other. That is why prioritising beats working through a long list. Here is what each one is, why it matters, and what acting on it looks like.

Blood pressure

Blood pressure is the single biggest lever. At a population level, the INTERSTROKE study associated high blood pressure alone with close to half of all strokes (O'Donnell et al., Lancet, 2016).

The problem is that it is almost entirely silent. Raised blood pressure produces nothing you can feel, while it quietly stiffens and damages arteries over years. Often the first sign is the event itself. So you cannot go on how you feel. You have to measure.

Measuring properly means more than one reading in a GP's surgery. A single clinic measurement says little about what your blood pressure does across the rest of the year, including how far everyday stress pushes it up, which for many people is significant and invisible on a one-off check. Knowing your numbers, in practice, means measuring regularly, at home, and watching the trend over time.

What should you aim for? The idea that matters is optimal rather than merely acceptable. The 2024 European Society of Cardiology guidelines classify a blood pressure below 120/70 mmHg as non-elevated, the low-risk range where medication is not indicated, and for anyone already on blood pressure treatment they aim for a systolic reading of 120 to 129 (ESC, 2024). Lower is not endlessly better, though. Blood pressure that runs too low leaves some people lightheaded and drained, so the right target for you is one to set with a clinician, aimed at the range where your risk is low and you still feel well.

Cholesterol, blood lipids and ApoB

Cholesterol travels through the blood inside particles, and it is the particles, not the cholesterol they carry, that lodge in an artery wall and build the plaque a clot can later form on. ApoB is essentially a count of those particles, which is why it maps more directly onto arterial risk than a standard cholesterol number. In INTERSTROKE, an ApoB-based ratio was the strongest lipid predictor of ischaemic stroke, and the signal was stronger still in people who had a stroke young (O'Donnell et al., Lancet, 2016).

A standard cholesterol check can miss two things. The first is a mismatch between your LDL cholesterol and your actual particle count. The two usually track together, but they can come apart in people with insulin resistance, whose particles carry less cholesterol each (Sniderman et al., 2014). That leaves a normal-looking LDL result sitting on top of a high particle count, so the number reads reassuring while the real risk is raised. Looking at ApoB rather than LDL alone closes that gap.

The second is lipoprotein(a), or Lp(a). It is not on the usual test, it is largely inherited, it is raised in roughly one in five people, and it barely moves with diet or exercise (Kronenberg et al., European Atherosclerosis Society consensus, 2022). Because it does not change, you only need to measure it once. But it is worth measuring, because otherwise it stays invisible while it quietly shifts your risk.

Blood sugar and insulin sensitivity

This one matters more than most people realise, because insulin resistance is the connector that ties the other factors together rather than a separate problem off to the side. It can raise ApoB, it can stiffen blood vessels by disrupting the signalling that keeps them relaxed, and once blood sugar itself runs high, that sugar can damage the lining of the vessels directly. One upstream problem, several downstream levers moving at once. It builds silently over years, which is exactly why it is worth catching early. (We go deeper on this in our guide to insulin resistance and blood sugar. [Internal link to be added: insulin resistance / diabetes post.])

Which markers show what is going on? The most direct read on insulin sensitivity is fasting insulin measured alongside fasting glucose. HbA1c is a useful supporting marker, but it is not one to lean on alone, because it can read falsely low or falsely high depending on things like red blood cell lifespan. Markers that reflect how the liver is handling insulin, such as SHBG, ALT and GGT, add to the picture. None of these are simple pass or fail cut-offs. The read is a gradient, and a result that is higher but still inside the "normal" range can still be telling you something.

Heart rhythm and atrial fibrillation

Atrial fibrillation is worth understanding because of one specific mechanism. Normally the upper chamber of the heart contracts and pushes blood cleanly onward. In atrial fibrillation it does not contract properly, it quivers, and blood that should be moving is left to pool. Pooled blood can clot, and that clot can break loose and travel to an artery in the brain. It is the same principle as a clot forming on a stagnant plaque, or in a leg on a long-haul flight: blood that stops moving is blood that can clot.

It often goes unnoticed, because it can come and go, and an episode may pass with only a flutter, a skipped beat, some breathlessness, or nothing you would notice at all. It is also strongly linked to age, so it is uncommon between 30 and 45 and becomes more common later in life (Wolf et al., Framingham Study, 1991). For most readers in this age group it is more a case of knowing it exists and watching for it later than a present concern.

The important point is this. If you do have atrial fibrillation, it is not something to manage yourself. It needs proper assessment by a clinician. So if you notice a persistently irregular or racing pulse, palpitations, or unexplained breathlessness, treat that as a reason to get checked rather than something to wait out or try to fix with lifestyle alone.

Lifestyle: what moves the numbers

Everyday habits all matter, but they do not matter equally, and the point of ranking them is to stop you spreading your effort across six things when two would do most of the work.

Quit smoking first. This is the one item on the list that is not a judgment call, because it works against your blood pressure, your ApoB and your clotting risk all at once, and everything else works better once it is gone.

After that, the biggest levers are diet quality and physical activity. A whole-food diet and regular movement improve insulin sensitivity and blood pressure, and pull ApoB down as a side effect of the same fix. Alcohol comes lower down the list for most people, not because it is harmless but because it is usually the smaller lever, and it matters more the more someone drinks.

So the short version of where to spend your effort: sort out smoking, get diet and activity genuinely right, and treat alcohol in proportion to how much you actually drink. A few sustained changes beat a long list you cannot keep up.

Sleep

Sleep belongs alongside diet and activity, and it matters most for insulin sensitivity. Poor sleep works against the very factors you are trying to improve. Sleep apnoea deserves a specific mention, because it can push blood pressure up and is closely tied to insulin resistance. It is worth taking seriously, and improving diet and activity often helps it too. If you snore heavily, gasp at night, or wake up unrefreshed, that is worth raising with your GP.

Where stroke prevention advice usually falls short

Most stroke advice is a generic checklist. It is not wrong, but it leaves the same gaps for almost everyone.

The first is blood pressure. Most people do not know their numbers and do not take them seriously, even though it is the single biggest factor and completely silent.

The second is insulin sensitivity. Most people are effectively blind to it, because the standard checks either skip it or read it through a single marker that can mislead.

Then there are two traps in how results get read. Treating a "within range" result as good enough is one. A reference range is simply the middle of a population that mostly has not been diagnosed with a disease. It is not proof that you are optimal, and for several markers a "normal" result can sit on top of real, ongoing risk. Normal is not the same as optimal.

Relying on a single check is the other. A one-off reading is a snapshot, but what drives risk is cumulative exposure over years. Someone whose blood pressure or ApoB has quietly sat above the line for fifteen years carries a very different risk from someone who crossed it last month, even though a single test of each can look identical. This is where the real value lies: measure the factors that matter directly, track them over time, and check whether the actions you are taking are actually moving them.

Where Calibre fits

If the problem with generic advice is that it cannot tell you which factors are raised for you, that is the gap Calibre is built to close.

Calibre helps you identify which of these risk factors are actually elevated in your own data, and turns that into a prioritised plan rather than another checklist. It is clinician-led, delivered with a CQC-regulated clinical partner, so the picture is read by people qualified to read it. And because risk is about your trajectory rather than a single snapshot, it is built around tracking your factors over time, so you can see whether what you are doing is working.

It fits at the point where you stop guessing and decide you want to know your own numbers, and what to do with them.

Putting this into action

Prevention here means lowering your risk by acting on what is driving it. The starting point is understanding your own measurable risk factors, blood pressure first, then the markers that sit underneath it, including ApoB and your insulin sensitivity, and Lp(a) once. From there, the work is turning those numbers into a short, prioritised plan you can actually keep to, and tracking whether it is moving the needle.

And it is worth remembering what this is all for. The goal is not chasing your next lab result or trying to live to 120. It is protecting your trajectory, so you keep the energy and capability to do the things you love, well into later life. Prevention is the tool. A long, capable life is the point.

FAQs

Can you actually prevent a stroke, or only lower your risk? No one can guarantee you will never have a stroke. What you can do is shift the odds a long way in your favour by acting on the factors you can measure, especially if you start early. Research into the modifiable risk factors links them to the majority of strokes, which is why prevention is best thought of as changing the odds rather than promising an outcome.

What are the main risk factors for a stroke? The ones you can influence are blood pressure, insulin sensitivity, blood lipids (particularly ApoB) and clotting factors. Alongside them sit factors you cannot change, such as age, family history and some inherited markers.

Which stroke risk factors can you change, and which ones can't you? You can influence blood pressure, insulin sensitivity, ApoB and clotting risk, through lifestyle and, where needed, medication. You cannot change your age, your family history, or inherited markers like Lp(a). But you can still optimise everything around the fixed ones, which reduces your overall risk.

What everyday habits increase your risk of a stroke? Smoking is the biggest, because it works against several factors at once. A poor diet, too little activity, and poor sleep, including untreated sleep apnoea, all raise risk too. Alcohol matters in proportion to how much you drink.

How can you reduce your stroke risk if it runs in your family? A family history raises your starting point, it does not remove the levers. Measure what can be measured, keep the controllable factors in good order (blood pressure, ApoB, insulin sensitivity, not smoking), and get Lp(a) checked once, so you know whether it is part of your picture.

What is the single most important number to know for stroke risk? Blood pressure. It is the biggest factor and it is silent, so measuring it, at home and over time rather than in a single clinic reading, tells you something you cannot feel.

Can you have stroke risk factors without any symptoms? Yes, and this is the point. High blood pressure, raised ApoB, insulin resistance and even atrial fibrillation can all be present with nothing you would notice. That is why measuring beats relying on how you feel.

How is preventing a stroke different from managing an existing condition? The mechanisms and the levers are the same. Without a diagnosis you are upstream of the problem, which is where the leverage is greatest. With a diagnosis, the same work is done alongside a clinician, often with medication added, with the priority on stopping a first event from becoming a second.

What should you do if you spot the signs of a stroke? That is an emergency, not a prevention question. Learn the FAST test (face, arms, speech, time) and call 999 straight away if you suspect a stroke in yourself or anyone else. Acting fast is what protects the brain.

References

1. O'Donnell MJ, Chin SL, Rangarajan S, et al. Global and regional effects of potentially modifiable risk factors associated with acute stroke in 32 countries (INTERSTROKE): a case-control study. Lancet. 2016;388(10046):761-775.

2. McEvoy JW, Touyz RM, et al.; ESC Scientific Document Group. 2024 ESC Guidelines for the management of elevated blood pressure and hypertension. European Heart Journal. 2024;45(38):3912-4018.

3. Kronenberg F, Mora S, Stroes ESG, et al. Lipoprotein(a) in atherosclerotic cardiovascular disease and aortic stenosis: a European Atherosclerosis Society consensus statement. European Heart Journal. 2022;43(39):3925-3946.

4. Wolf PA, Abbott RD, Kannel WB. Atrial fibrillation as an independent risk factor for stroke: the Framingham Study. Stroke. 1991;22(8):983-988.

5. Sniderman AD, et al. Apolipoprotein B and the discordance between LDL cholesterol and particle number, concentrated in insulin resistance. Journal of Clinical Lipidology, 2014 (with Witt et al., Diabetes, Obesity and Metabolism, 2025).