Half the People With High Blood Pressure Don't Know It: How to Find Out If You're One of Them

September 27, 2026

A study published on September 23 in BMJ Public Health looked at the blood pressure readings of 1.4 million adults in England and found high blood pressure in 37 percent of them. Among the people who had it, 59 percent had never been told. No diagnosis and no prescription. And of the people already taking a pill for it, half were still above the line the study drew.

Two days later the Washington Post ran the story under a headline saying that over half of people with hypertension don’t know they have it, which is how many of you will have seen it. Those are English numbers, and my first question was whether they travel. They do. Our own national survey, in which the CDC measures the blood pressure of a sample of Americans with a proper protocol, puts the share of adults with high blood pressure at nearly half, and four in ten of them have never been told either.

When this comes up in clinic, the question I get is some version of “wouldn’t I feel it?” The answer is no, almost never. What follows is why that is, what a single reading can and cannot tell you, and how to find out where you stand without waiting for a symptom that is not coming.

What the study measured

Our Future Health is a British research program that has signed up more than two and a half million volunteers. Those who attend an appointment get their height, weight, blood pressure, and heart rhythm recorded by clinic staff. Researchers at Oxford Population Health took the blood pressure readings from 1.4 million adults enrolled between 2022 and 2025 and asked three questions. How many had hypertension? How many of those knew? And of the ones on treatment, how many were controlled?

They used the World Health Organization’s definition, which is a top number of 140 or higher, a bottom number of 90 or higher, or already being on a blood pressure medication. That is a looser standard than the one we use in the United States, and I’ll come back to why that makes the American picture worse.

Thirty-seven percent had hypertension. Fifteen percent of the 18-to-39-year-olds, rising to 71 percent of those 80 and older. Men were almost 50 percent more likely to have it than women once the researchers adjusted for age, 42 percent against 29.

Of everyone with hypertension, 59 percent were undetected, meaning they had never been diagnosed and were on no medication. Nearly two-thirds. Among those taking one or more blood pressure medications, 50 percent were still at 140 over 90 or above. Wenyu Liu, the statistician who led the analysis, said the current approach to detecting and treating high blood pressure “is not fit for purpose.” Bryan Williams of the British Heart Foundation supplied the number that turns the statistic into a problem. High blood pressure is linked to around half of heart attacks and strokes in the UK.

Doctors used to call this the rule of halves, with half of the people who had high blood pressure undiagnosed, half of the diagnosed treated, and half of the treated controlled. England’s serial national surveys showed it improving toward a rule of two-thirds by 2011. The new numbers look a lot more like the old rule.

Two things about the design deserve a mention, because they pull in opposite directions. Participants were volunteers who answered an invitation, and volunteers for health studies tend to be healthier and more engaged than the people who ignore the letter. Against that, the readings came from one appointment, and pressure measured once, on one day, runs high in a fair number of people whose pressure is fine at home, which inflates the count of people who look undiagnosed. England’s own national health survey, which draws a representative sample of households, has put the undiagnosed share nearer one in three, and its authors make the same point about single-visit readings. So the exact figure for the whole population is uncertain. Every way anyone has measured it, a large share of the people with high blood pressure have never been told, and the American survey, which averages up to three readings, still finds four in ten.

The American numbers are no comfort

Every few years the CDC runs a survey called NHANES that does something no doctor’s office can. It sends a mobile examination center around the country, measures the blood pressure of a representative sample of Americans with a standard protocol, an average of up to three readings, and then asks each person whether a doctor has ever told them they have high blood pressure. Its most recent cycle covered August 2021 through August 2023.

Using the American definition of 130 over 80, 47.7 percent of adults had hypertension. Nearly half. Among them, 59.2 percent were aware of it, 51.2 percent were taking medication, and 20.7 percent had it controlled to below 130 over 80.

Run that backwards and it reads the way the English study reads. Four in ten American adults with high blood pressure have never been told. Eight in ten are above target. Put those two figures together and more than half of the people walking around this country with uncontrolled high blood pressure have no idea, which is the arithmetic behind a JAMA headline from 2024 that said exactly that. And of the people taking a pill, roughly six in ten were still above 130 over 80, by my arithmetic from the survey’s own figures.

What bothers me most is the age pattern. Among 18-to-39-year-olds with hypertension, only 27 percent knew. Among 40-to-59-year-olds, 57 percent. Past 60, 74 percent. The younger you are, the more likely your high blood pressure is a secret, and the more years it has to do its work before anyone notices. Men were less likely to know than women, 55 percent against 64.

None of this is improving.

Awareness, treatment, and control were all flat compared with the survey cycle before the pandemic. And the pattern is global. By the World Health Organization’s estimate, 1.4 billion adults between 30 and 79 have hypertension, about 44 percent of them do not know, and 23 percent have it under control. A 2026 analysis that pooled 287 studies from around the world landed in the same place, with awareness at 51.5 percent, treatment at 39 percent, and control just under 20 percent. Half the people on earth with high blood pressure do not know it, and one in five has it handled.

England’s numbers are the world’s numbers with a British accent.

Why you can’t feel it

Blood pressure is the force your blood exerts on the walls of your arteries, and nothing in the wall of an artery reports sustained pressure to your brain as a sensation. Nothing hurts. Nothing is short of breath. A person with a reading of 165 over 100 usually feels exactly the way they felt at 118 over 76, which is the whole problem. Old stories about headaches, nosebleeds, and a flushed face describe a small minority of people at very high pressures, and as a screening test they miss almost everyone.

What happens instead happens slowly. Extra pressure thickens and stiffens the artery wall over years. It makes the heart muscle work harder, and the muscle thickens in response the way any muscle does under load, except a thick heart wall is stiffer and fills less well. In the kidneys the small filtering vessels scar, a process described in how high blood pressure damages the kidneys. In the brain the same small-vessel damage shows up as strokes, some large and some so small they only register years later as a decline in memory. And the retina shows the damage before the person notices anything about their vision.

Few relationships in medicine are as well measured as the one between the number and the damage. A pooled analysis of a million adults found that between the ages of 40 and 69, every 20 points of extra top-number pressure roughly doubled the risk of dying from a stroke or from heart disease, with no floor below which more pressure was safe, down to about 115. What that means for you is the subject of blood pressure and death risk. The short version is that a pressure you cannot feel is doing arithmetic on your arteries every day, and the English study found that most of the people it is happening to have no idea.

One more consequence follows from the silence. Drugs for high blood pressure are cheap, generic, mostly once a day, and usually well tolerated. Lifestyle changes are known and they work. What the numbers say is that the bottleneck sits at the step before any of that, which is finding out.

What one reading can and can’t tell you

Before you run to the pharmacy kiosk, a caution that runs the other way. A single reading is a poor basis for a diagnosis, and the American guidelines say so outright.

Blood pressure moves. It rises when you talk, when you are cold, when you need the bathroom, when you have just walked in from the parking lot after twenty minutes on the 5, and when a stranger in a white coat is about to tell you a number. This office effect is real and measurable. Somewhere between 15 and 30 percent of people with elevated readings in a clinic have normal pressure everywhere else, a pattern called white coat hypertension. Their risk sits closer to normal than to hypertensive, and the guidelines do not recommend medication for it.

A reverse pattern exists too, and it is more dangerous. Some people read normal in the office and high at home and at work, which is called masked hypertension, and it turns up in a similar 15 to 30 percent of people with normal office readings. Because nobody sees the high numbers, nobody treats them. Their risk of a heart attack or stroke runs about double that of people with normal pressure, about the same as anyone else with untreated hypertension, and they are invisible to a screening program built on office readings alone.

So a single elevated reading at a kiosk or a clinic is a reason to measure properly, and a single normal one is reassurance with an asterisk. The American guidelines, both the 2017 version and the update published in August 2025, want the diagnosis confirmed with readings taken outside the office, at home or with a 24-hour monitor, before anyone starts a pill. So does the US Preventive Services Task Force. It is the standard I would want applied to my own numbers, and it is the reason the post on home monitoring exists.

How to find out where you stand

Start with the question of whether you have been measured at all. The task force recommends a reading at least every year past 40, and every year at any age for people who are overweight, whose readings have been in the elevated range, or who are Black, since hypertension starts earlier and is more common in Black Americans, close to six in ten adults at the 130 over 80 line. Between 18 and 39 with none of those, every three to five years is enough. If you cannot remember your last reading, you have your answer.

Then get a cuff of your own. A validated upper-arm monitor costs about what dinner out costs, and validated is the word that counts. Plenty of devices on the pharmacy shelf have never been tested against a reference standard. The American Medical Association keeps a free list of the ones that have, at validatebp.org, and I would not buy one that is missing from it. Skip wrist and finger devices. And skip the smartwatch for this purpose. In so many words, the 2025 guideline says cuffless devices, smartwatches included, are not to be relied on for blood pressure measurement, and I agree with it.

Get the cuff size right, because this is probably where more home readings go wrong than anywhere else. A trial at Johns Hopkins measured 195 adults with a standard adult cuff and then with the cuff that fit their arm. In people who needed a large cuff, the standard one read 4.8 points too high on the top number. In people who needed an extra-large cuff, it read 19.5 points too high, enough to turn an average reading of 125 over 79 into 144 over 87 and manufacture a diagnosis of stage 2 hypertension out of nothing. Fewer than a third of the people in that study fit a standard cuff. Measure around your upper arm with a tape before you buy, and check that number against the arm range printed on the box.

Then measure the way the studies measure, because technique moves the number as much as the device does. Sit in a chair with your back supported and your feet flat on the floor for five quiet minutes first. No coffee, exercise, or cigarettes in the previous half hour, and an empty bladder. Rest your arm on a table so the cuff sits at the level of your heart. That last one is not fussiness. The same Hopkins group ran a second trial in which the arm rested on the lap or hung at the side, and the lap added 3.9 points to the top number while the hanging arm added 6.5. Six and a half points is the difference between 123 and 130, or between 133 and 140. Do not talk during the reading. Take two readings a minute apart and write both down.

Do that twice in the morning before coffee and medication, and twice in the evening, for seven days. Then average everything, and if you want to follow the formal protocol to the letter, throw out the first day, when most people are still learning the routine. Your average is the number, and the outliers are noise. One reading of 152 after an argument tells you that you had an argument. A seven-day average of 138 tells you that you have hypertension. The full protocol, including what happens to the readings once you have them, is in why I ask so many patients to monitor at home.

What the average means, under the 2025 American guideline. Below 120 over 80 is normal. A top number of 120 to 129 with a bottom number under 80 is elevated, which is a warning and not yet a disease. Stage 1 hypertension is a top number of 130 to 139, or a bottom number of 80 to 89. Stage 2, the same threshold the English study used, is a top number of 140 or higher, or a bottom number of 90 or higher. Either number qualifies on its own, so a reading of 122 over 86 is stage 1 on the strength of the bottom number.

If your average lands at 130 over 80 or above, bring the log to a doctor and have the conversation. Stage 2 means medication for nearly everyone. Whether stage 1 means a pill right away depends on your overall risk, which is a calculation any doctor can run in a minute from your age, cholesterol, and a few other numbers. At lower risk the guideline gives lifestyle changes three to six months to work first, and reaches for medication if the average is still at 130 over 80 after that. If your average lands in the elevated range, you are the person with the most to gain from salt, weight, alcohol, and exercise, which is the subject of weight loss, exercise, and blood pressure, and you are the person the drugs were never meant for.

If you already take a pill for it

Half of the treated people in England were above 140 over 90. By my arithmetic from the CDC survey, about six in ten treated Americans are above 130 over 80. If you take a blood pressure medication and have not measured at home lately, the odds that you are one of them are not small.

Most of the reasons are ordinary. Reaching target takes more than one medication for most people, about three in four by the usual estimate, and in the largest blood pressure trial ever run only three in ten got there on a single drug. Both American guidelines say so outright, and the 2025 version has stage 2 starting on two drugs in a single pill for that reason. Doses get set at a first visit and never revisited. Side effects lead people to quietly stop, and swollen ankles on amlodipine, the subject of a post on that exact side effect, is a common one. Some pills fight the medication. Ibuprofen and naproxen raise blood pressure by a few points on average, more in people taking an ACE inhibitor, and they blunt most classes of blood pressure drugs, as described in NSAIDs and the heart. Decongestants do the same. Salt and alcohol both push the number up. Untreated sleep apnea keeps it up all night, and it is present in most people whose pressure will not come down on three drugs. And a minority of people have a specific, findable cause, an adrenal gland making too much of a hormone, a narrowed kidney artery, a thyroid problem, which is the territory of secondary hypertension. The most common of those, an adrenal condition called primary aldosteronism, affects perhaps one in twenty people with high blood pressure and one in five of those whose pressure resists treatment. Fewer than two in a hundred of the people who should be tested for it ever are, and it responds to a cheap old drug, spironolactone.

Beta-blockers deserve their own line, because a lot of people are on one for blood pressure alone. The 2025 guideline does not list them as a first-line choice for hypertension without another reason to use one, which I wrote about in do you still need that beta-blocker. If your regimen was built years ago and has not been reviewed since, a home log is the fastest way to find out whether it is doing its job.

What works best for getting treated people to target is boring. Home monitoring plus someone on the other end who adjusts the medication between visits, a nurse or a pharmacist working with the doctor, beats home monitoring alone, which beats the usual pattern of a reading every six months and a shrug. In pooled trials that model, with a nurse or pharmacist doing the adjusting, brought the top number down about ten points more than usual care, and a cuff wired to a phone app with nobody on the other end did no better than the cuff alone. That model is what the 2025 guideline built its recommendations around. New pharmacology is arriving for the people who stay high on three drugs, including the aldosterone-blocking pill covered in a post on baxdrostat, though the common problem is old drugs that were never adjusted, and that is fixable with a cuff and a phone call.

What I would tell you

If you have not had your blood pressure measured in a year, get it measured, and treat any number at or above 130 over 80 as a reason to buy a cuff and measure properly for a week. If you are under 40 and healthy, do not file this under later. Three in four young adults who have it do not know, and arteries do not wait for the diagnosis.

If you take a pill for it and could not tell me your home average, you are guessing, and the English study says the guess is a coin flip. A week of readings costs nothing and settles it.

And if the average is high, do the ordinary things and take them seriously, because they work, and then have the medication conversation with a doctor, whether that is with me here in Encinitas or with your own. Bring the log. A week of numbers from your kitchen table is worth more to that conversation than anything measured in the ten minutes after you have found parking.

Frequently Asked Questions

Can you feel high blood pressure?

No, almost never. Headaches, nosebleeds, and a flushed face describe a few people at very high pressures and miss the vast majority, which is why so much of it goes undetected. In the CDC’s examination survey four in ten American adults with hypertension had never been told, and in the English study of 1.4 million adults it was 59 percent. The only way to know is to measure. If you cannot remember your last reading, that is the reading to get.

What number counts as high blood pressure?

Under the American guideline updated in 2025, normal is below 120 over 80. Elevated is a top number of 120 to 129 with a bottom number below 80. Stage 1 hypertension is 130 to 139 on top or 80 to 89 on the bottom, and stage 2 is 140 or higher on top or 90 or higher on the bottom. Either number qualifies on its own. A diagnosis should rest on an average of readings taken properly over several days, never on a single number.

The pharmacy machine said 148 over 94. Do I have hypertension?

Maybe. One reading, in a public place, with a cuff that may not fit your arm, is a reason to measure properly and is not a diagnosis. Between 15 and 30 percent of people with high readings in a clinic setting have normal pressure everywhere else. Buy a validated upper-arm cuff, measure twice each morning and evening for a week using the technique described above, and take the average to your doctor. If the average is 130 over 80 or higher, you have your answer.

Is a wrist monitor or a smartwatch good enough?

No. Wrist devices are far more sensitive to arm position and read less reliably in ordinary use. Smartwatches and other cuffless devices estimate blood pressure from pulse signals and have not shown the accuracy needed to diagnose or manage hypertension, and the 2025 American guideline advises against relying on them for that purpose. Use a validated upper-arm cuff from the American Medical Association’s list at validatebp.org, and make sure the cuff fits your arm.

How often should a healthy person get checked?

Every year from age 40, says the US Preventive Services Task Force, and every year at any age for people who are overweight, whose readings have been in the elevated range, or who are Black. Between 18 and 39 with none of those risk factors and prior normal readings, every three to five years is enough. A yearly physical covers this, which is one more reason to keep having one.

I take a blood pressure pill. Why would it still be high?

Because most people need more than one medication to reach target, and a dose that was set years ago may never have been adjusted. Salt, alcohol, ibuprofen and naproxen, decongestants, poor sleep, and untreated sleep apnea all push the number up. A minority of people have a specific cause such as an overactive adrenal gland. In the English study half of the people on treatment were still above 140 over 90, and the fix in most cases is adjusting what you already take, guided by a home log.

The study was in England. Does it apply in the United States?

Yes, and the American picture is worse because the United States uses a lower threshold. For 2021 to 2023 the CDC’s examination survey found hypertension in 47.7 percent of American adults at the 130 over 80 definition, with 59 percent aware, 51 percent treated, and 21 percent controlled. Only 27 percent of 18-to-39-year-olds with hypertension knew they had it. The World Health Organization’s global estimate is that 44 percent of adults with hypertension do not know, so the English finding is close to the norm.

References

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2. University of Oxford, Oxford Population Health. “Two-Thirds of Adults With High Blood Pressure Do Not Know They Have It.” Press release, September 23, 2026.

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21. Adler, Gail K., Michael Stowasser, R. R. Correa, et al. “Primary Aldosteronism: An Endocrine Society Clinical Practice Guideline.” Journal of Clinical Endocrinology and Metabolism (2025).

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Published on damianrasch.com. The above information was composed by Dr. Damian Rasch, drawing on individual insight and bolstered by digital research and writing assistance. The information is for educational purposes only and does not constitute medical advice.