# Low Diastolic Blood Pressure: What a Low Bottom Number Means

Published: 2026-10-20

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Understand Your Numbers

# Low diastolic blood pressure: what a low bottom number means

After 50, the bottom number often drifts down while the top one climbs. Here’s what a low diastolic reading is measuring, what pulls it down, and why “below 60” on a home monitor is a conversation with your GP rather than an emergency.

[NK Medically reviewed by Dr Nouman Kazmi, MBBS FCPS](https://getmatter.co/pages/matter-cardiologist-dr-syed-nouman-kazmi)
·10 min read

## Key Takeaways

* The NHS and the British Heart Foundation both define low blood pressure as a reading below 90/60mmHg. That’s the pair of numbers, not the bottom one on its own.
* Diastolic pressure is the pressure while the heart rests between beats. Harvard Health notes it often declines after age 50, as arteries become less elastic and don’t spring back as easily after each push.
* Harvard Health puts the goal for most older adults at a systolic close to 120, as long as the diastolic stays at 60mmHg or higher. That 60 is the number to know.
* Blood pressure medicines are one of the common reasons a bottom number sits low. The NHS says changing medicines or altering a dose is something a GP recommends, so it’s a conversation, never a self-adjustment.
* The BHF says most people with low blood pressure have no noticeable symptoms. Dizziness, feeling sick, blurred vision, tiredness or fainting are what make it worth getting checked.

In This Article

1. [What counts as a low bottom number](#what-counts)
2. [What the bottom number actually measures](#what-it-measures)
3. [Why it falls while the top number climbs](#why-it-falls)
4. [What else pulls it down](#what-pulls-it-down)
5. [When it is worth a conversation](#when-to-ask)
6. [What to log before you see your GP](#before-the-gp)
7. [Frequently asked questions](#faq)
8. [The bottom line](#bottom-line)

## What counts as a low bottom number

Every home monitor shows two numbers, and almost every piece of advice is about the first one. So when the second number starts reading in the 50s, there isn’t an obvious place to go and look it up.

Start with the definition that does exist. The NHS describes low blood pressure, hypotension, as a reading of less than 90/60mmHg, and the British Heart Foundation uses the same figure. Both are talking about the whole reading. A diastolic of 58 sitting underneath a systolic of 150 doesn’t meet that definition, and it isn’t what either page is describing.

Which leaves a gap, and it’s the gap most people land in. The bottom number can read low on its own, with a top number that’s perfectly ordinary, or one that’s high in its own right, and none of the standard advice really speaks to it. Harvard Health is straightforward about why: doctors tend to focus on the top number, for good reason, and the bottom one “tends to get overlooked”.

The UK reference points run the other way too. The NHS considers blood pressure high at 140/90 or higher when a healthcare professional checks it, or 135/85 or higher when you check it at home. Those are ceilings, and they’re what a GP is looking at. Neither the NHS nor the BHF publishes an equivalent floor for the diastolic number by itself.

90/60

**mmHg is where the NHS and the BHF both draw the line for low blood pressure, and it’s a pair of numbers.** A low bottom number underneath a normal or high top number falls outside that definition, which is exactly why it’s so hard to look up.

## What the bottom number actually measures

Systolic pressure is the pressure in the arteries while the heart contracts and pushes blood out. Diastolic is the pressure during the heart’s resting phase between beats. Harvard Health describes a healthy diastolic pressure as critical for the coronary vessels to supply the heart muscle with enough oxygen.

That last line is the one to hold onto, because it’s what explains why the bottom number matters at all. Dr Jason Guichard, a cardiologist at the University of Alabama at Birmingham, sets out the mechanism in an interview with UAB News: most of your arteries feed your organs during systole, but the coronary arteries sit around the aortic valve and get blood only when that valve closes, which happens in diastole. A low diastolic pressure means a low coronary artery pressure, which means the heart muscle is doing its work on less blood and oxygen than it would like.

## Why it falls while the top number climbs

Here’s the pattern that brings most people to this question. The top number has been creeping up for years, and the bottom number has quietly been heading the other way.

Harvard Health explains it through the arteries themselves. Systolic pressure tends to increase with age as blood vessels weaken and narrow, while diastolic pressure often declines after age 50, because arteries become less elastic. An artery that’s gone stiff expands with the systolic push but doesn’t spring back as easily between heartbeats, so the pressure in the gap between beats drops. Harvard also names endothelial dysfunction, where the coronary arteries on the heart’s surface constrict instead of opening, as another possible cause.

Guichard describes the same change from the clinic side: as you get older your vessels become a little more stiff, and that tends to push the systolic number up and the diastolic number down.

If the top number is the one out of range while the bottom one stays normal, there’s a name for that too: isolated systolic hypertension. Harvard describes it as a common type of high blood pressure in older adults, happening because less elastic arteries have trouble accommodating surges of blood.

💡

One change, two numbers

The stiffening that pushes the top number up is the same stiffening that lets the bottom number fall. It’s one change in the arteries showing up twice on the same display, which is why the two figures say more as a pair than either does on its own. That’s the case for writing both numbers down rather than just the top one.

## What else pulls it down

Age and arterial stiffness are the slow version. A handful of other things turn up on the list, and some of them are a good deal more fixable.

* **Medicines.** The BHF lists heart medicines, high blood pressure medicines and water pills, or diuretics, among the causes of low blood pressure, and notes that medicines for Parkinson’s disease and erectile dysfunction increase the risk of orthostatic hypotension. Guichard names alpha blockers and centrally acting agents as the classes most likely to pull the diastolic down further than the systolic.
* **Dehydration.** The BHF’s explanation is a mechanical one. When your body does not have enough water, there is less blood travelling around it.
* **Other conditions.** The BHF names Parkinson’s disease, diabetes and other heart conditions, including heart failure and bradycardia, alongside endocrine disorders, where hormones such as cortisol help to regulate blood pressure.
* **Blood loss and pregnancy.** Both change the volume of blood or the width of the vessels carrying it. The BHF notes blood pressure should return to how it was before pregnancy after giving birth.
* **Simply being you.** The NHS points out that blood pressure may be low because you’re fit and healthy, or because you inherited it from your parents, and that some people develop low blood pressure as they get older.

⚠

**If a tablet looks like the reason, that’s still your GP’s call.** The NHS says that where a cause for low blood pressure can be found, a GP will be able to recommend what to do about it, and that this can mean changing medicines or altering the dose. The BHF asks you to speak to your doctor before making any changes to your lifestyle, diet or exercise routine. Bring the readings. Don’t adjust anything on the strength of them.

## When it is worth a conversation

Most of the time the honest answer is that a low bottom number gets kept an eye on, and not much else. The BHF says most people with low blood pressure have no noticeable symptoms at all.

Symptoms are what change the picture. The NHS says to get your blood pressure checked if you keep getting lightheadedness or dizziness, feeling sick, blurred vision, generally feeling weak, confusion or fainting, and to see a GP if symptoms such as dizziness and fainting keep coming back. The BHF’s version of the list adds feeling tired. If the symptoms arrive when you stand up or change position suddenly, the NHS says that may be postural hypotension, a type of low blood pressure with its own name and its own pathway.

The research is where that “below 60” figure comes from. A 2011 paper in the journal Hypertension by Guichard and Ali Ahmed, described in the same UAB News interview, coined the term “isolated diastolic hypotension” for a diastolic below 60mmHg sitting under a systolic that is still normal, which they put at above 100mmHg. Older adults who fitted that description, they found, were at increased risk of developing new-onset heart failure.

A 2023 cohort study in the Journal of Clinical Hypertension followed 25,858 US adults whose blood pressure was already inside the recommended range, which the study defined as under 130mmHg systolic and under 80mmHg diastolic. Within that group, a diastolic below 60mmHg was associated with a higher risk of death from any cause than a diastolic between 70 and 80mmHg, with a hazard ratio of 1.30 (95% confidence interval 1.12 to 1.51). It helps to know who that figure doesn’t describe. If your top number is 150, you wouldn’t have been in that cohort at all. It describes people whose systolic was already fine.

There’s a second half to that study, and it’s the half that matters if you take blood pressure medicines. When the researchers split the group by medication, a diastolic below 60 in people *not* taking blood pressure medicines carried the raised risk, at a hazard ratio of 1.46 (95% confidence interval 1.21 to 1.75). In people whose diastolic sat below 60 while on blood pressure medicines, it did not, at a hazard ratio of 0.99 (95% confidence interval 0.73 to 1.36). Their reading of it was that the risk was already there, and bringing the diastolic down a little further with medication didn’t add to it.

Guichard’s own emphasis is the same one. His point about watching the bottom number is that nobody should be driving their numbers down so far they can’t play with their grandchildren or walk round the block. He calls anything between 60 and 90 good in an older adult. Below 60 is where people start to feel uncomfortable, and that’s where he thinks a closer look belongs.

## What to log before you see your GP

Guichard’s answer, for people whose medicines can’t be changed, is closer monitoring: more frequent appointments, and an eye on any cardiovascular or heart failure symptoms. That’s a job a home monitor happens to be good at, and it’s the part you can arrive with already done.

* **Both numbers, every time.** A diastolic on its own tells a GP far less than the pair does.
* **Same time of day, same technique.** The NHS notes blood pressure varies depending on the time of day, so two readings only compare if they were taken the same way. We’ve set the method out in [how to measure blood pressure correctly at home](https://getmatter.co/blogs/heart-health/how-to-measure-blood-pressure-correctly-at-home).
* **Any symptom, next to the reading it belongs to.** Dizzy standing up, tired by mid-afternoon, a near-faint in the kitchen.
* **Every medicine you take**, including anything you buy over the counter.

Then leave it alone for a few weeks. One low morning is noise. Six to eight weeks of readings taken the same way is what turns a handful of numbers into a trend, and a trend is the thing a GP can work with. If a check has already suggested your blood pressure might be high, the NHS says you may be asked to use a monitor at home over the next few days, to come back for another check, or to wear a portable monitor that takes readings across 24 hours. [What happens during a 24-hour blood pressure monitor on the NHS](https://getmatter.co/blogs/heart-health/24-hour-blood-pressure-monitor-nhs) covers that appointment.

Separately from all of this, the NHS says to get help from 111 if you often have headaches or blurred vision, or chest pain that comes and goes. It says to call 999 for sudden chest pain or discomfort that does not go away, for pain spreading to your arm, neck, jaw, stomach or back, or for chest pain alongside sweating, feeling sick, lightheadedness or breathlessness. Those aren’t bottom-number questions.

Matter BP Tracker

## Two numbers, logged for *weeks*.

The bottom number only makes sense next to the top one, and the pair only makes sense across weeks. The Matter BP Tracker keeps both figures, the dates and the symptoms you noted beside them in one place, so what you hand your GP is a trend rather than a memory.

[Open the BP Tracker →](https://tracker.getmatter.co?utm_source=resource_centre&utm_medium=article&utm_campaign=low-diastolic&utm_content=tracker_section)
Both numbers·Charted over weeks

## Frequently asked questions

What is a low diastolic blood pressure?

The NHS and the British Heart Foundation both define low blood pressure as a reading below 90/60mmHg, and that figure covers the whole reading, bottom number and top. Neither body publishes a figure for the diastolic alone. The number that recurs in the clinical literature is 60. Harvard Health puts the goal for most older adults at a systolic close to 120, as long as the diastolic stays at 60mmHg or higher, and the research on low diastolic pressure uses below 60mmHg as its cut-off.

Why is my diastolic low when my systolic is high?

Usually the arteries. Harvard Health explains that systolic pressure tends to increase with age as blood vessels weaken and narrow, while diastolic pressure often declines after age 50, because a stiffer artery expands with each push but doesn’t spring back as easily between beats. It’s one change in the arteries, and two numbers moving in opposite directions.

Is a diastolic of 55 dangerous?

It’s a GP conversation rather than an emergency. The BHF says most people with low blood pressure have no noticeable symptoms. What changes the picture is symptoms, and the NHS says to get your blood pressure checked if you keep getting lightheadedness or dizziness, feeling sick, blurred vision, generally feeling weak, confusion or fainting. Take a few weeks of readings to the appointment, because one low morning on its own doesn’t tell anybody much.

Can blood pressure tablets make the bottom number too low?

They can be part of it. The BHF lists high blood pressure medicines, heart medicines and water pills among the causes of low blood pressure, and a 2023 study in the Journal of Clinical Hypertension found antihypertensive use was associated with a diastolic below 60mmHg. Never change a dose yourself. The NHS says that once a cause has been found, a GP will be able to recommend what to do about it, and that can mean changing medicines or altering the dose. That call is theirs.

Does a low diastolic reading mean something is wrong with my heart?

Not on its own. The reason clinicians watch it is that the coronary arteries are supplied during diastole, so Harvard Health describes a healthy diastolic pressure as critical for those vessels to deliver oxygen to the heart muscle. Research has linked a diastolic below 60mmHg with higher risk in older adults, but that’s an association measured across large groups, not a reading of your heart. What helps is a few weeks of logged readings and a GP appointment.

## The bottom line

A bottom number drifting down while the top one climbs is usually the arteries getting stiffer, and it’s the most overlooked thing on a home monitor’s display. It isn’t a number to panic about, and it isn’t a number to ignore either. Write down both figures at the same time each day, note any dizziness or tiredness beside them, keep going for six to eight weeks, and take the trend to your GP. That’s the version of this a GP can do something with. Changing a dose is their decision. Having the readings ready is yours.

## Continue Learning

[📚

Understanding

The Complete Guide to Understanding Blood Pressure (UK)](https://getmatter.co/blogs/heart-health/the-complete-guide-to-understanding-blood-pressure-uk)
[📊

Numbers

Normal Blood Pressure by Age: A UK Guide](https://getmatter.co/blogs/heart-health/normal-blood-pressure-by-age)
[🧪

Measuring

How to Measure Blood Pressure Correctly at Home](https://getmatter.co/blogs/heart-health/how-to-measure-blood-pressure-correctly-at-home)

**Medically reviewed by Dr Nouman Kazmi**
Consultant Cardiologist (MBBS, FCPS). Dr Kazmi reviews clinical content on the Matter Heart Health Resource Centre for accuracy.

[View Dr Kazmi’s profile →](https://getmatter.co/pages/matter-cardiologist-dr-syed-nouman-kazmi)

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## References

1. NHS. Low blood pressure (hypotension). Page last reviewed 11 July 2023. Available at: [nhs.uk](https://www.nhs.uk/conditions/low-blood-pressure-hypotension/)
2. NHS. High blood pressure (hypertension). Available at: [nhs.uk](https://www.nhs.uk/conditions/high-blood-pressure-hypertension/)
3. British Heart Foundation. Low blood pressure: causes and symptoms. Published 25 June 2024. Available at: [bhf.org.uk](https://www.bhf.org.uk/informationsupport/risk-factors/high-blood-pressure/low-blood-pressure)
4. Harvard Health Publishing. A look at diastolic blood pressure. Reviewed by Mallika Marshall MD, 2 April 2026. Available at: [health.harvard.edu](https://www.health.harvard.edu/heart-health/a-look-at-diastolic-blood-pressure)
5. Wang Z, Yu C, Cao X, He Y, Ju W. Association of low diastolic blood pressure with all-cause death among US adults with normal systolic blood pressure. J Clin Hypertens (Greenwich). 2023;25(4):326–334. Available at: [pmc.ncbi.nlm.nih.gov](https://pmc.ncbi.nlm.nih.gov/articles/PMC10085810/)
6. UAB News. Diastolic blood pressure: how low is too low? Interview with Jason Guichard MD PhD, 17 May 2015. Available at: [uab.edu](https://www.uab.edu/news/research-innovation/diastolic-blood-pressure-how-low-is-too-low)

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Tags: blood pressure, diastolic, heart health, home monitoring, understanding your numbers

Source: https://getmatter.co/blogs/heart-health/low-diastolic-blood-pressure