Key Takeaways
- Low diastolic blood pressure is generally a diastolic reading below 60 mm Hg.
- The coronary arteries fill between beats, so a very low diastolic number can leave the heart muscle itself under-supplied.
- Common causes include aging and stiffer arteries, dehydration, over-treatment with blood pressure medication, and heart valve problems.
- When a low diastolic number sits next to a normal or high systolic number, it widens the pulse pressure, and that wider gap is linked to higher cardiovascular risk.
- The occasional low reading without symptoms is usually nothing urgent. Dizziness, fainting, or chest pain alongside a low bottom number are a different matter and need medical review.
Below 60 mm Hg, the bottom number of a blood pressure reading may be too low to push enough blood into the heart's own arteries, which fill between beats.
You take a reading like 120/55. The top number looks fine, and the bottom one is lower than you have seen before. Low diastolic blood pressure is a diastolic reading below 60 mm Hg, the pressure in your arteries between heartbeats, when the heart rests and refills. A single low reading is common, and often it is harmless. But the bottom number does its own job, and a very low one can matter for the heart. This guide walks through what the number means, what causes it, when it turns dangerous, and how a wide pulse pressure fits into the bigger picture of heart health.
What Is Low Diastolic Blood Pressure?
Low diastolic blood pressure is a diastolic reading below 60 mm Hg. Diastolic pressure is the bottom number, the arterial pressure between beats while the heart relaxes and refills with blood.
A blood pressure reading has two numbers, written as one over the other, something like 120/80 mm Hg. The top number is systolic pressure, the peak pressure while the heart contracts and pushes blood out. The bottom number is diastolic pressure, the resting pressure between beats. Here is why that resting phase matters so much: it is when the coronary arteries, the vessels feeding the heart muscle, receive most of their blood supply. So the diastolic number is really a read on how well the heart itself is fed.
The bottom number is not just a passenger to the top one. A 2019 analysis in the New England Journal of Medicine of more than 1.3 million adults found that both the systolic and the diastolic number independently predicted heart attack and stroke risk. For reference, a normal diastolic number sits below 80 mm Hg under the 2017 ACC/AHA guideline, so a reading under 60 is well beneath the usual resting range.
What Causes Low Diastolic Blood Pressure?
Low diastolic blood pressure is most often caused by aging and stiffer arteries, dehydration, over-treatment with blood pressure medication, or a heart valve problem.
Age-related arterial stiffening is a leading driver. Rigid arteries tend to raise the systolic number while pulling the diastolic one down. Low blood volume plays a part too, and dehydration is a common cause of low blood pressure. Blood pressure medication can also overshoot, especially vasodilators and diuretics, which is why a diastolic number that keeps running low is worth reviewing with the prescriber.
Then there are the structural and systemic causes. Aortic valve regurgitation, where blood leaks back into the heart between beats, can drop the diastolic number specifically. Autonomic and orthostatic problems, prolonged bed rest, blood loss, and thyroid or adrenal conditions can lower blood pressure as well. The NHLBI lists dehydration, medications, heart problems, and diabetes among the general causes of low blood pressure, and several of those show up first in the bottom number.
Low Diastolic Number and Wide Pulse Pressure
A low diastolic number alongside a normal or high systolic number produces a wide pulse pressure, the gap between the top and bottom numbers.
Pulse pressure is the systolic number minus the diastolic number. A StatPearls overview of pulse pressure physiology puts a typical pulse pressure at about 40 mm Hg, and readings above roughly 60 mm Hg are widely regarded as wide. So a reading of 120/55 gives a pulse pressure of 65, which already sits in the wide range, even though the top number looks perfectly ordinary.
Stiffer arteries with age are the most common reason the gap widens, since they push systolic pressure up and pull diastolic pressure down at the same time. Aortic regurgitation and other high-output states can widen it too. And the gap is not just a curiosity. A 1999 Framingham Heart Study analysis found that a wider pulse pressure predicted higher coronary heart disease risk. It sounds technical, but it matters. Treat a wide pulse pressure as a marker worth noting, not a diagnosis on its own.
Is Low Diastolic Blood Pressure Dangerous?
A diastolic reading below 60 mm Hg can matter because the heart's own arteries fill between beats, so very low diastolic pressure may reduce the heart muscle's own blood supply.
The evidence points in a consistent direction. A 2016 analysis from the ARIC study, published in the Journal of the American College of Cardiology, linked diastolic pressure below 60 mm Hg to subclinical heart muscle damage and more coronary events. And in people already being treated for high blood pressure and coronary artery disease, a 2006 analysis of the INVEST trial in Annals of Internal Medicine tied excessively low diastolic pressure to more cardiac events. That pattern has a name, the J-curve.
Context is what decides how much a low diastolic number matters. For many people, especially younger adults, a naturally low bottom number without any symptoms is not itself an emergency. Age, symptoms, existing heart disease, and blood pressure medications all shape the risk, which is part of how blood pressure ties into heart health. A low reading in a healthy 25-year-old and the same number in a treated heart patient are simply not the same situation.
Symptoms and When to See a Doctor
Low diastolic blood pressure often causes no symptoms, but when it does, the most common are dizziness, lightheadedness, fatigue, blurred vision, and fainting, according to the NHLBI.
See a doctor for repeated low diastolic readings, and pay attention to whether symptoms track with them. Persistent dizziness, ongoing fatigue, or heart palpitations alongside a low bottom number are all worth raising. Seek prompt care for fainting, chest pain, shortness of breath, or confusion with a low reading, since those can signal that organs are not getting enough blood. And do not stop any prescribed blood pressure medication on your own. That is a decision for the clinician who prescribed it.
Frequently Asked Questions
What is a dangerously low diastolic blood pressure?
A diastolic reading below 60 mm Hg is generally considered low, and the risk grows as it falls further, especially in people with coronary artery disease. A 2016 ARIC analysis linked diastolic pressure below 60 to heart muscle damage and more coronary events. In a healthy person with no symptoms, a low bottom number is often not an emergency. But readings paired with dizziness, chest pain, or fainting need prompt medical review.
What causes a low diastolic blood pressure?
Low diastolic blood pressure is most often caused by aging and stiffer arteries, dehydration and low blood volume, over-treatment with blood pressure medication, or a leaking aortic valve. Vasodilators and diuretics can push the bottom number down, and blood loss, prolonged bed rest, and thyroid or adrenal problems can contribute as well. Because the causes range from harmless to serious, a persistently low diastolic number is worth checking with a doctor.
What does a low diastolic number mean?
A low diastolic number means the pressure in your arteries between heartbeats has dropped below the usual resting range, generally under 60 mm Hg. Since the coronary arteries fill during that resting phase, a very low diastolic number can mean the heart muscle receives less of its own blood supply. On its own, one low reading usually means little, but a repeated low bottom number is worth tracking with a clinician.
What are the symptoms of low diastolic blood pressure?
Low diastolic blood pressure often causes no symptoms at all. When symptoms do appear, the most common are dizziness, lightheadedness, fatigue, blurred vision, and fainting, because the brain and other organs briefly receive less blood. Chest pain, shortness of breath, or confusion with a low reading are more concerning and warrant prompt care. Many people only discover a low bottom number when they check their blood pressure for some other reason.
What does a wide pulse pressure indicate?
A wide pulse pressure, the gap between the systolic and diastolic numbers, usually indicates stiffer arteries and is often driven by aging or a leaking aortic valve. A typical pulse pressure is about 40 mm Hg, and above roughly 60 mm Hg is considered wide. A 1999 Framingham analysis found a wider pulse pressure predicted higher coronary heart disease risk, so it is a useful marker to mention to your doctor rather than a diagnosis by itself.
Below 60 mm Hg is the general line for a low diastolic number, and the core concern is straightforward: a very low bottom number can under-supply the heart's own arteries. A wide pulse pressure is a related warning marker, one that points to stiffer arteries. For many healthy people a low reading without symptoms is not urgent. But age, existing heart disease, medications, and symptoms together are what decide how much any single low diastolic reading really matters.