Could You Have High Blood Pressure Without Knowing It?

TL;DR

• High blood pressure is easy to miss. In the new study, 37% of participants met the researchers' definition of hypertension, and 59% of those cases were previously undetected.
• Age made an enormous difference. Prevalence ranged from 15% among adults aged 18–39 to 71% among those aged 80 or older.
• Men were more likely to have it. After adjusting for age, prevalence was 42% in men and 29% in women.
• Treatment didn't always mean control. Half of participants taking at least one blood-pressure medicine still recorded 140/90 mmHg or higher.
• One high reading doesn't diagnose hypertension. NICE recommends confirming most raised clinic readings with 24-hour ambulatory monitoring or repeated measurements at home.
• The thresholds differ by where you measure. Hypertension is generally confirmed at an average of 135/85 mmHg or above at home or during daytime ambulatory monitoring, following a raised clinic reading.
• The useful response is to know your numbers. High blood pressure usually causes no symptoms, so measuring it is the only reliable way to know whether it may be high.

What Did the New Study Find?

Researchers at Oxford Population Health analysed blood pressure measurements from about 1.4 million adults enrolled in the Our Future Health programme in England between 2022 and 2025, in an unusually large snapshot of how hypertension is detected and treated. Published in BMJ Public Health, it classified someone as having hypertension if their systolic pressure was at least 140 mmHg, their diastolic pressure at least 90 mmHg, or they reported taking blood-pressure-lowering medication. On that definition, 37% had hypertension.

The age gradient was striking: 15% of people aged 18–39 met the definition, rising to 71% of those aged 80 or older. After age standardisation, hypertension was also substantially more common among men than women, at 42% versus 29%. But the most important finding was not how many people had a high reading. It was how many did not know. Among participants classified as having hypertension, 59% had not previously been diagnosed and were not taking blood-pressure medication.

There was a second gap among people who already knew they had a problem. Of those taking one or more blood-pressure medicines, 50% still recorded blood pressure of at least 140/90 mmHg. The researchers argue that hypertension in England is being missed and inadequately controlled on a very large scale, describing a "leaky cascade of care" between detection and control, and noting that prevalence today looks similar to two decades ago.

A High Reading Isn't Necessarily Hypertension

Blood pressure is not a fixed number. It changes through the day and responds to exercise, stress, sleep, caffeine, alcohol, medication and illness, and some people experience the white-coat effect, where blood pressure is substantially higher in a clinical setting than outside it. That matters here, because participants had their blood pressure measured at an Our Future Health clinic appointment, and for the population-level analysis a reading of 140/90 mmHg or above counted towards the definition of hypertension.

Clinical diagnosis in England is more demanding. Under NICE guidance, a clinic reading between 140/90 and 179/119 mmHg is normally followed by ambulatory monitoring (ABPM), using a monitor worn for around 24 hours, or by repeated measurements at home if ABPM is unsuitable or declined. Hypertension is then generally confirmed when the clinic reading is at least 140/90 and the daytime ambulatory or home average is at least 135/85 mmHg.

So the study does not establish that 37% of adults in England would all receive a clinical diagnosis if assessed through the full NICE pathway. Earlier English estimates make the point: Office for National Statistics analysis of the Health Survey for England put prevalence at around 32%, with roughly 29% of cases undiagnosed, against 59% here. That gap reflects a single clinic reading rather than a confirmed diagnosis, a volunteer cohort rather than a representative sample, and a definition of undiagnosed that means no prior diagnosis and no medication. None of which makes the finding unimportant: a very large number of people produced a reading high enough to warrant further investigation.

Why Would You Not Know?

Because hypertension usually does not announce itself. It is possible to have substantially elevated blood pressure and feel completely normal, and while headaches, blurred vision and chest pain can occur, symptoms are unusual enough that waiting for them is a poor way to detect the condition. That is why the NHS describes measurement as the only way to find out. The damage meanwhile accumulates gradually, as persistently elevated pressure strains blood vessels and organs including the heart, brain, kidneys and eyes, raising the risk of heart attack, stroke, heart failure, kidney disease and vascular dementia. The absence of symptoms is not evidence that your blood pressure is normal.

What Do the Numbers Mean?

Blood pressure is recorded as two numbers: systolic pressure, in your arteries when the heart contracts, and diastolic pressure, while it relaxes between beats. So 128/78 mmHg means a systolic pressure of 128 and a diastolic pressure of 78. For diagnosis in England, the important distinction is between clinic readings and out-of-clinic readings, and the NICE stages use both. Stage 1 hypertension means a clinic reading of 140/90 to 159/99 mmHg alongside a daytime ambulatory or home average of 135/85 to 149/94. Stage 2 means a clinic reading of 160/100 or above, but below 180/120, alongside an average of 150/95 or above. A clinic measurement of 180/120 mmHg or higher is treated differently and needs prompt clinical assessment rather than a week of home monitoring. The important word throughout is average: diagnosis is about a pattern of elevated pressure, not a single measurement. If the two numbers themselves are unfamiliar, our guide to understanding blood pressure readings walks through them in more detail.

How Should You Measure Blood Pressure at Home?

Home monitoring replaces one snapshot with a series of measurements under normal conditions, but technique matters. Sit down and relax with your arm supported, and put the cuff around your upper arm rather than over clothing. The NHS advises taking a reading, recording it, waiting a minute and taking another, usually twice daily over several days as instructed. NICE's protocol is more specific: two consecutive seated measurements a minute apart, twice daily, ideally for seven days and at least four, with the first day discarded and the rest averaged. If you are buying a monitor, choose an upper-arm device with the correct cuff size, because one that has not been clinically validated can give a reassuringly precise number without giving an accurate one. If a reading is unexpectedly high, sit quietly and repeat it rather than treating the first result as a diagnosis, and speak to your GP practice or pharmacist if repeated measurements stay high. Very high readings are different: NICE defines severe hypertension as a clinic systolic pressure of 180 mmHg or above or a diastolic of 120 or above, which needs prompt clinical assessment, and chest pain, severe breathlessness or anything suggesting a heart attack or stroke needs urgent medical attention whatever a home monitor says.

What About the Half Already Taking Medication?

This may be the more uncomfortable finding. Among participants taking one or more blood-pressure medicines, half still recorded 140/90 mmHg or above. That does not mean half of hypertension treatment is failing: the study measured blood pressure on one occasion, and relied on participants reporting their own medication use rather than on prescribing records. There are also ordinary reasons someone on treatment might record a high number, from a dose that needs adjusting to normal day-to-day variability. At population level, though, the finding matters: finding hypertension is only the first step, and keeping it controlled is a separate problem.

Who Should Get Checked?

You don't need to buy a monitor because this study exists, but you should know roughly where your blood pressure sits. The NHS advises a check if you think you may be at increased risk, and specifically for people aged 40 or over who haven't had one in more than five years — an interval we have looked at before. Many pharmacies offer free checks for the over-40s, and GP surgeries and some workplaces also measure it. Alongside age and family history, the NHS lists Black African, Black Caribbean and South Asian background, excess weight, smoking, high salt intake, excessive alcohol and long-term stress among factors linked to higher blood pressure.

The new study is also a reminder not to treat hypertension as purely an older person's condition, since 15% of participants aged 18–39 met its definition. That is not the same as 15% of young adults having confirmed hypertension, since this is a volunteer cohort rather than a random sample, but youth is no guarantee of normal blood pressure.

What This Actually Means

The most alarming reading of this study would be that 37% of adults in England have hypertension and most don't know it. The more precise reading is that in an enormous research cohort, more than one in three adults either recorded at least 140/90 mmHg or were already taking medication, and 59% of those had not previously been diagnosed or treated. Because hypertension normally needs confirmation with repeated out-of-clinic measurements, the study cannot show that every undiagnosed participant truly had persistent hypertension. It does show that high readings are extraordinarily common, and that many people who record them are not being treated.

The researchers' proposal points somewhere more specific: towards more proactive detection and treatment decisions that consider predicted cardiovascular risk alongside blood pressure itself. That fits a separate Oxford analysis presented at the European Society of Cardiology Congress in August, which found similar relative benefits from blood-pressure lowering across the range of cardiovascular risk. Whether UK guidelines move further in that direction is a question for NICE. For an individual deciding what to do this week, the response is simpler: measure again.

Frequently Asked Questions

Can you have high blood pressure and feel completely healthy?

Yes. High blood pressure usually causes no symptoms, so feeling well doesn't tell you whether your blood pressure is normal.

Is one reading of 140/90 hypertension?

Not usually. In England, a clinic reading of 140/90 mmHg or above and below 180/120 normally triggers confirmation using 24-hour ambulatory monitoring or repeated home measurements. An average daytime or home reading of 135/85 mmHg or above can then confirm hypertension.

How often should I check my blood pressure?

If your clinic blood pressure is below 140/90 mmHg, NICE advises checking at least every five years, and more often when it is close to that threshold. The NHS advises people aged 40 or over who haven't had a check in more than five years to get one.

Can high blood pressure be lowered?

Yes. Reducing excess salt, exercising regularly, losing excess weight where appropriate, limiting alcohol and not smoking can all help. Many people also need blood-pressure-lowering medication, sometimes more than one. Diet has a measurable role too, as our look at beetroot juice and blood pressure shows.

The Bottom Line

The headline from England's largest study of its kind is hard to ignore: 59% of participants meeting its definition of hypertension didn't know they had it. The qualification matters just as much, because a single elevated clinic measurement isn't normally enough to diagnose hypertension, and this study shouldn't turn one unexpected reading into a medical condition. What it should do is make knowing your blood pressure feel less optional. The number takes minutes to measure, repeated measurements can establish whether there is really a problem, and if there is, hypertension is something medicine already knows a great deal about reducing. The difficult part is finding it.

If you want structured support for the habits that sit underneath blood pressure — sleep, movement, salt, alcohol and stress — the Reset Series offers step-by-step programmes, and Reset Companion can help you adapt them to your own week.

This article is for general information and does not replace individual medical advice.