New

125/75 Is Not A Normal Blood Pressure

-Morgan McSweeney, PhD

A large patch of our lawn died over the summer during a stretch of unusually intense heat and watering restrictions in our area. So, this week my daughter (2 years old) and I are taking on the project of thinning out the dead spots, mixing in some new soil, putting down new grass seed, topping with a little fresh dirt, and then covering lightly with straw. This is a great joy for both of us - an opportunity to get thoroughly dirty and exhausted, and to learn something about biology in the process.

When I think about my health, the timeline that I am optimizing for has nothing to do with the next 3 or 5 years. I am thinking about how to improve my capacity for when my daughter is twenty, thirty, forty, and fifty years old so that I can still be doing new outdoors projects with her then, as I am now.

Of everything I have read about long-term health, blood pressure may be the number that most of us underrate. They don’t call it a silent killer for nothing.

About half of US adults have high blood pressure, but only about 6 in 10 of those people are aware that they have high blood pressure.

Note: I have just finished writing this letter, and I’ve circled back to the top to add this: I think this topic is one of the most important things you’ll read this month. If you do not know what your current blood pressure is, and which risk category that puts you in, I encourage you to take this topic very, very seriously.

This blood pressure deep dive is more than a book chapter in length, and it will be truncated if you are reading in your email app. If the letter appears to cut off suddenly, you’ll have to either click “View entire message” to load the rest of the email, or scroll back up to the top of this letter now and click the title to open it in your browser. Or, read in the substack app.

The good news is that blood pressure is among the most treatable things in modern medicine (with lifestyle factors, medications, or a combination of both).

But, before you can treat it seriously, you have to know whether yours is elevated in the first place.

The risks associated with high blood pressure compound over time. On any given day, having a blood pressure of 145/90 is not likely to cause any noticeable symptoms at all. However, it becomes serious trouble when your cardiovascular system is subjected to that increased pressure over the course of years (and decades). I think of risk in terms of cumulative exposure to those higher pressures (unless it is either extremely high or low, in which case it can cause immediate and sometimes life-threatening outcomes).

A few years back, I realized that I had never properly measured my own blood pressure. Sure, I get it checked once a year when I see my primary care provider, but I had never measured it outside of the stressful context of the doctor’s office, and I’d never measured it multiple times in one day, let alone multiple days in one week. Further, I did not know where to purchase a reputable device that could give me reliable results at home. Last, I didn’t know all of the various ways that you can accidentally skew the results of a reading.

Using a blood pressure cuff that is one size too small for your arm adds about 5 points to your reading. Two sizes too small adds about 20 points! That is from a randomized trial published in 2023.

That is just one of many ways a reading can be wrong. Talking during the measurement, sitting with your legs crossed, letting your arm hang, recently having had caffeine, needing to pee: each one has been measured for its effect on the accuracy of your reading.

A home cuff (when used correctly) is one of the most useful pieces of health equipment you can own, for under $100. However, a home cuff that is used incorrectly (or not at all) doesn’t help you out very much.

Today, in the extended section, I have prepared a 7-day protocol (with a printable chart/guide) for you to properly measure your blood pressure at home, to inform your next discussion with your doctor. I also recommend a $75 validated home blood pressure device that I suspect would provide data just as reliable as the one I bought for $179.

One safety note on exceptionally high readings: if you ever see a reading above 180/120 (a top number over 180 or a bottom number over 120) along with chest pain, shortness of breath, back pain, numbness or weakness, a change in vision, or trouble speaking, call 911; do not wait to see if it comes down. With no symptoms, wait one minute and measure again. If it is still above 180/120, you should still call your doctor right away, even after hours. And call 911 whatever the cuff says if any of these come on suddenly: chest pain or shortness of breath, or numbness or weakness, a change in vision, or trouble speaking. It’s that serious. (If you are pregnant or had a baby in the last 6 weeks, the threshold for where it is “urgent” is lower: a reading of 140/90 or higher (either number), a headache that won’t go away, or a change in vision means calling your OB or midwife right away, and at 160/110 or higher (either number), or if you can’t reach them quickly, go to the hospital or call 911.)

In a US study of adults classified before age 40, stage 2 blood pressure came with about 3.5 times the cardiovascular risk of normal blood pressure

The ACC/AHA categories are in the table below. If your two numbers land in different categories, the higher category counts. So for example, if your pressure is 125/82, that counts as stage 1.

Some data on risk by blood pressure category comes from the CARDIA study, which sorted about 4,850 adults by the highest category they reached at clinic exams before age 40 and followed them for a median of 19 years:

The takeaway here is that the “old” thresholds you may have in your head for where blood pressure starts to increase risk (e.g., “above 140”) are probably too conservative.

As it turns out, even having a pressure of 125/75, putting you in the elevated category, is associated with ~1.7-fold higher risk of a cardiovascular event, compared to being under 120 and under 80.

(This is observational data in younger adults. Absolute rates of cardiovascular events climb steeply with age, and the last column is adjusted for other risk factors, which is why it is smaller than the raw rates suggest.)

Lowering systolic pressure (the first, or upper number in a blood pressure reading) by 10 points cut major cardiovascular events by 20% across 123 trials

Blood pressure has some of the strongest treatment evidence in all of medicine. A meta-analysis of 123 randomized trials covering 613,815 people found that every 10 mmHg reduction in systolic pressure (the first, or top number in a blood pressure reading) cut major cardiovascular events by 20% (relative risk 0.80, 95% CI 0.77 to 0.83), stroke by 27%, heart failure by 28%, and death from any cause by 13%.

The grave danger with all of this is that you feel the same at a pressure of 133/85 as you do at 119/75. However, as those risk data indicate, your arteries do not.

Ten common factors each pushed systolic readings up, from a few mmHg to more than 20

A 2017 systematic review went through 328 studies of what distorts a resting blood pressure reading and found 27 factors with a measurable effect. The figure below shows the significant effects that review reported on systolic pressure. Note that wide bars mean there was a lot of uncertainty in the estimated effect size.

In most of my experience, my prior blood pressure readings at my primary care doctor went something like this: I make myself a coffee at home, drive to the doctor, walk in from the parking lot, go up a flight of stairs to the clinic, sit in the cold waiting room for ~5-10 minutes, then sit on the exam table with nothing behind my back while a nurse wraps the cuff on my arm while asking me about my weekend.

Many errors are in play at once!

And that’s not even to mention my general “white coat” anxiety that I feel in the clinic. (Yes, I experience white coat anxiety despite having a wife who is a physician, and despite being fully aware that most healthcare providers are humans, too.)

The review’s conclusion was that “a single BP value outside the expected range should be interpreted with caution,” and the 2017 ACC/AHA guideline accordingly says to “use an average of ≥2 readings obtained on ≥2 occasions” to estimate a person’s blood pressure.

That is what I have now done with a validated device at home, and it resulted in an estimated average reading that was literally 15 points lower than my most recent single measurement taken at my primary care doctor’s office.

Caffeine’s effect on blood pressure shows up within about 30 minutes, peaks at 1 to 2 hours, and can last more than 4

The AHA’s current advice for patients tells you to avoid caffeine for 30 minutes before you measure your blood pressure, and so did the home-monitoring table in the 2017 ACC/AHA guideline. I find that odd, because 30 minutes after consumption is about when caffeine’s effect on your blood pressure is just getting started.

In 2008, two researchers at South Dakota State University reviewed the research on exactly this question. Caffeine peaks in your blood 30 to 120 minutes after you drink it, and its half-life is 3 to 6 hours. Blood pressure typically starts climbing within about 30 minutes, peaks at 1 to 2 hours, and may stay up for more than 4 hours after caffeine, by roughly 3 to 15 points systolic in the earlier reviews they summarized (close to the caffeine bar in the chart above), and by more in people who already have high blood pressure.

Their verdict was that abstaining for 30 minutes “is not adequate to avoid caffeine’s potential effects” on blood pressure, and that even 60 minutes “appears too short,” because it “would coincide with the time frame in which the peak blood pressure effect is usually observed.” Many daily coffee drinkers develop some tolerance, but how much varies a lot, and some still get a clear rise (one of the studies they cited was titled “Caffeine Tolerance is Incomplete: Persistent Blood Pressure Responses in the Ambulatory Setting”).

So, by the official rules, the coffee in my pre-appointment routine above was perfectly fine, as long as I finished it 30 minutes before the cuff went on. But by the pharmacology, the cuff would have gone on right as the caffeine was maximally pushing my numbers up. If anything, I suspect a reading taken 3 minutes after a coffee would land closer to my caffeine-free number than one taken an hour later, right at the peak. (I am not recommending that)

My guess is that the “30 minutes” rule stuck because it is a wait a clinic can actually enforce (nobody is going to keep you in a waiting room for 4 hours, though admittedly some days it feels close). When measuring at home, you and I have no such excuse. Take your morning reading before your first coffee, tea, or energy drink, which fits right in with taking it before your morning medications. For the evening reading, ideally have your last caffeine at least 4 hours earlier (longer is better), and if you didn’t manage to leave that much of a time gap, take the reading anyway but write down when you had the caffeine as a note.

If you drink caffeine all day long, though, your blood pressure is running higher for a lot of the day, and that counts from your arteries’ perspective, so it’s worth measuring anyway. Keep those evening readings in your average, with the note, and let your doctor read them in context.

Of the 30-minute rules, only the one for cigarettes appears to hold up; after exercise, readings run low for hours

The 2017 guideline lists three things to avoid for 30 minutes before a reading: caffeine, exercise, and smoking. For a cigarette, 30 minutes seems about right: in a small randomized trial, systolic pressure stayed up for about 15 minutes after one (and for about 45 minutes after vaping nicotine). Exercise errs in the other direction. After you’ve cooled down from a workout, blood pressure tends to dip 5 to 8 points below its usual number and can stay there for up to a day, so a reading taken 30 minutes after the gym will flatter you.

As a side note, how cool is it that doing exercise gives you a lasting decrease in blood pressure? Add this to one of the many mechanisms through which daily physical activity can improve your health long-term – it’s literally giving your blood vessels a break for hours after each bout of activity.

Alcohol is not on the 30-minute list, even though a Cochrane review of 32 trials found that it lowers blood pressure for several hours, and that after heavier drinking it later swings higher. The simplest fix covers all of these: take your morning reading first thing, before coffee, food, medications, nicotine, a workout, etc.

So what is your real number, and if it turns out to be high, what actually brings it down?

This letter has no ads, no sponsors, and I have no relationship with any blood pressure monitor or wearable company; I will point you toward the validated device list and I will tell you which one I personally bought ($179), but there’s no affiliate link for that product. In fact, I will nudge you toward a $75 option that I suspect would be just as useful as mine.

That’s the entire point of running my letter as fully reader-supported. You can have confidence that when I name a specific product I have tried, you can take it at face value; there is no ulterior financial motive.

In today’s extended section:

The quick summary: a 4-point list of what you should do
The 7-day protocol the AHA and AMA specify: how many readings, at what times, for how many days, and what to do with the numbers at the end.
[Printable] A one-page blood pressure log sheet to print out and keep next to the cuff, with a row for your average and a list of the readings that would mean “call someone right now.”
How to choose a home machine, including the validated $75 option that I would trust about the same as my $179 machine.
How to size the cuff for your arm in 30 seconds with a tape measure, and the cuff dimensions the AHA statement specifies.
Brief description of evidence-based lifestyle factors to lower your blood pressure: the eating pattern plus salt cut that lowered systolic pressure by 5 to 21 points, the kind of exercise you can do against a wall in a few minutes, the salt swap that cut strokes in a 21,000-person trial, and what being “salt-sensitive” means in practice.
The 180/120 rule: the list of symptoms that mean “call 911 right away,” the blood pressure finding that means re-measure once and then call your doctor (180/120), and the mistake to not make in between.

A paid subscription also opens the full archive, including

Subscribe now

The paid tier of my letter is $12 a month, or $8 a month via the annual plan ($96 a year). I choose my topics and write my deep dive letters with the intention of making the rate feel deeply worth it, with respect to the health insights you will gain over the course of the year.

If you subscribe and then find it is not useful, call me a silly name (I can take it) and then cancel in one click.

Nothing you measure at home is a reason to change, skip, or add a blood pressure medication that your doctor recommended. If you already take a medication and one day you find that your readings are much lower than usual and you feel dizzy or lightheaded, call your doctor the same day (even if it’s after hours), before taking your next dose.

Back to Listing

credit: