Key Takeaways
- Diastolic pressure is the bottom number: the pressure in your arteries between heartbeats.
- Under the 2017 ACC/AHA guideline, normal is below 80 mm Hg; 80-89 is stage 1 hypertension and 90 or higher is stage 2.
- High diastolic pressure on its own (isolated diastolic hypertension) shows up most often in adults under 50.
- Below 60 mm Hg, diastolic pressure may be too low to keep the heart's own arteries supplied.
- The same measures lower both numbers: the DASH diet, less sodium, exercise, weight loss, and less alcohol.
Nearly half of US adults, about 120 million people, have high blood pressure, and most of them are reading the bottom number wrong.
You check your blood pressure and it says 118/88. The top number looks fine. So what is the bottom one telling you? That lower figure is your diastolic pressure, and here is the part that catches people off guard: high diastolic blood pressure counts as hypertension even when the top number is completely normal.
Diastolic blood pressure is the pressure in your arteries between heartbeats, when the heart rests and refills. It is the bottom number in a blood pressure reading. This guide walks through what counts as normal, high, and low, what tends to cause each, and what actually brings it down.
What Is Diastolic Blood Pressure?
Diastolic blood pressure is the pressure blood exerts on your artery walls between heartbeats, while the heart muscle relaxes and refills. Something important happens during that resting phase: the coronary arteries, the ones feeding the heart muscle itself, fill with blood right then. That is why the bottom number carries more weight than most people assume.
Systolic pressure, the top number, measures the force against your artery walls when the heart contracts and pushes blood out. Diastolic pressure measures the force between those contractions. A reading gets written as systolic over diastolic in millimeters of mercury. So 120/80 mm Hg means a systolic of 120 and a diastolic of 80. Simple enough on paper.
Both numbers carry real risk information. A 2019 analysis of 1.3 million adults in the New England Journal of Medicine found that systolic and diastolic hypertension each independently predicted heart attack and stroke. A high bottom number is not just noise. It signals risk all on its own.
Normal Diastolic Blood Pressure by Category
Normal diastolic blood pressure is below 80 mm Hg, alongside a systolic reading below 120 mm Hg. Those thresholds come from the 2017 guideline issued by the American College of Cardiology and the American Heart Association, and that guideline lays out five categories.
| Category | Systolic (top number) | Diastolic (bottom number) |
|---|---|---|
| Normal | Below 120 | and below 80 |
| Elevated | 120-129 | and below 80 |
| Stage 1 hypertension | 130-139 | or 80-89 |
| Stage 2 hypertension | 140 or higher | or 90 or higher |
| Hypertensive crisis | Above 180 | and/or above 120 |
These ranges match the American Heart Association's blood pressure reading chart. And both numbers count. Whichever one lands in the worse category, that sets your overall category. Take 118/88 again: that reading is stage 1 hypertension even though the systolic is perfectly normal.
How you measure matters as much as what you measure. Sit quietly for five minutes first, keep your arm supported at heart level, and take readings on multiple days. One high reading is not a diagnosis; doctors confirm high blood pressure with repeated readings over time, not a single number caught on a bad morning.
High Diastolic Blood Pressure: What It Means
A diastolic reading of 80 mm Hg or higher counts as high blood pressure, even when the top number is normal. When the bottom number runs high but the systolic stays below 130, doctors have a name for that pattern: isolated diastolic hypertension.
Isolated diastolic hypertension is most common in adults under 50. There is a reason for that. As arteries stiffen with age, systolic pressure tends to climb and take over as the dominant problem, so an isolated high bottom number is mostly something younger adults see.
What Causes High Diastolic Blood Pressure?
High diastolic blood pressure is associated with excess sodium, alcohol, excess body weight, inactivity, smoking, stress hormones, sleep apnea, thyroid and kidney disease, and certain medications. The contributors that come up most often:
- A high-sodium diet
- Heavy alcohol use and smoking
- Excess body weight and physical inactivity
- Stress hormones such as adrenaline and cortisol
- Sleep apnea
- Thyroid or kidney disease
- Certain medications
Fluid status can play a role too. It turns out dehydration can raise blood pressure in some people, worth knowing if your readings tend to spike on days you drink very little.
Researchers are still arguing about how risky an isolated high bottom number really is. A 2020 cohort analysis in JAMA found that isolated diastolic hypertension, defined by the 2017 thresholds, showed no significant association with more cardiovascular events. The larger 2019 analysis described above found the opposite: diastolic pressure predicts risk on its own. That unresolved debate is exactly why guidelines treat 80-89 mm Hg as stage 1 and weigh treatment against your other risk factors rather than reaching for medication automatically.
Low Diastolic Blood Pressure: When the Bottom Number Drops
Low diastolic blood pressure is generally a reading below 60 mm Hg. Why does a dropping bottom number deserve attention? It comes back to how the heart feeds itself. The coronary arteries fill between beats, so a diastolic pressure below 60 mm Hg may leave the heart's own blood supply running short.
That concern shows up in the data. A 2016 analysis from the Atherosclerosis Risk in Communities study, published in the Journal of the American College of Cardiology, linked diastolic pressure below 60 mm Hg to subclinical heart muscle damage and coronary events.
What Causes Low Diastolic Blood Pressure?
Low diastolic blood pressure is most often caused by age-related artery stiffening, dehydration, blood pressure medication overshoot, heart valve problems, or prolonged bed rest. Stiff arteries widen the gap between the two numbers. And dehydration is a common cause of low blood pressure for a plain mechanical reason: less fluid in the blood means less pressure between beats.
Watch for dizziness, fatigue, and fainting. The occasional low reading without symptoms is usually less concerning. Repeated dizziness alongside diastolic readings below 60 mm Hg is a different story and warrants a medical review, especially if you take blood pressure medication.
How to Lower Diastolic Blood Pressure
The same evidence-backed measures that lower systolic pressure lower diastolic pressure; no method targets only the bottom number, however much we might want one. These six steps have the strongest evidence behind them:
- Follow the DASH eating pattern. The DASH eating plan, from the National Heart, Lung, and Blood Institute, was built around vegetables, fruits, whole grains, and low-fat dairy specifically to bring blood pressure down.
- Cut sodium. The World Health Organization recommends staying under 2,000 mg of sodium per day, which works out to about 5 g of salt.
- Exercise regularly. A 2023 meta-analysis of 270 randomized trials found isometric exercise, think wall sits and planks, produced the largest reductions in resting blood pressure of any exercise type.
- Lose weight if you are overweight. Extra body weight raises blood pressure, and losing it can bring both numbers down.
- Limit alcohol and stop smoking. Both are linked to higher blood pressure, and cutting back works on the bottom number just as it does on the top.
- Manage sleep and stress. Poor sleep and chronic stress keep stress hormones elevated, and lowering chronically high cortisol supports the same goal.
Hydration cuts both ways, oddly enough. Too little fluid can push blood pressure up in some people and drop it in others, so a steady daily water intake supports stable readings.
If lifestyle change is not enough, doctors prescribe medication based on guideline thresholds and your overall risk. One thing you should never do is stop a prescribed blood pressure medication on your own; talk to your doctor before making any change.
When to See a Doctor
A reading above 180 systolic and/or above 120 diastolic is a hypertensive emergency when it comes with symptoms. Chest pain, shortness of breath, vision changes, or weakness alongside numbers that high means seek immediate care. Do not wait it out.
Book a regular appointment for repeated diastolic readings of 80-89 mm Hg, any reading paired with chest pain or breathlessness, heart palpitations, or repeated dizziness with low readings. And bring your home log. Measurements taken over several days tell your doctor far more than a single number ever could.
Frequently Asked Questions
What does high diastolic blood pressure mean?
High diastolic blood pressure means the pressure in your arteries between heartbeats is 80 mm Hg or higher, which counts as hypertension under the 2017 ACC/AHA guideline. Readings of 80-89 mm Hg fall into stage 1 hypertension, and 90 or higher into stage 2. When only the bottom number runs high, doctors call it isolated diastolic hypertension, and it is a pattern seen most often in adults under 50.
What is a dangerously low diastolic blood pressure?
A diastolic reading below 60 mm Hg is generally considered too low, because the heart's own coronary arteries fill between beats and may run short of blood below that level. Research has linked diastolic readings under 60 mm Hg to subclinical heart muscle damage. The occasional low reading without symptoms is less concerning. Readings below 60 with dizziness, fatigue, or fainting warrant prompt medical evaluation.
Can anxiety cause high diastolic blood pressure?
Yes, anxiety can raise diastolic blood pressure temporarily. Stress hormones such as adrenaline speed the heart and narrow blood vessels, which can push both numbers up for minutes to hours. The link between chronic anxiety and lasting hypertension is less direct, and honestly, still being studied. If anxious moments keep coinciding with your measurements, take readings at calm times on several days to find your true baseline.
How to raise diastolic blood pressure instantly?
There is no safe way to raise diastolic blood pressure instantly. If a low reading comes with dizziness, lying down with your legs raised, drinking fluids, and standing up slowly can ease symptoms while your body rebalances. Persistently low diastolic readings, especially below 60 mm Hg or while taking blood pressure medication, need a doctor's review rather than a quick fix; medication dosing is a common cause, and a correctable one.
How to lower diastolic blood pressure naturally and quickly?
Cutting sodium and adding isometric exercise, such as wall sits and planks, are the fastest natural approaches, with measurable reductions appearing within weeks. A 2023 meta-analysis of 270 randomized trials found isometric exercise the most effective exercise type for lowering resting blood pressure. Pair those with the DASH eating pattern, weight loss if needed, and less alcohol, and the drops in both numbers get larger and last longer.
The evidence on diastolic blood pressure is consistent on the big points. Both numbers in a reading matter. 80 mm Hg is the line where the bottom number counts as high, and readings below 60 mm Hg deserve attention too. The lifestyle measures with the best evidence, from the DASH diet to isometric exercise, lower both numbers together and remain the foundation of long-term heart health.