Diastolic Blood PressureUnderstanding the Bottom Number

When you see a blood pressure reading like 120/80 mmHg, the bottom number—80 in this case—is your diastolic blood pressure. While the top number (systolic) often gets more attention, the diastolic reading provides crucial information about your cardiovascular health, particularly the pressure your arteries experience when your heart is at rest between beats.

Understanding diastolic blood pressure helps you interpret your readings accurately and recognize when intervention may be needed. Though its role in cardiovascular risk has been debated over the years, we now know that both numbers matter—sometimes in different ways depending on your age and health circumstances.

What Diastolic Blood Pressure Represents

Your heart works in a rhythmic cycle of contraction and relaxation. When it contracts (systole), it pushes blood out into your arteries, creating the higher pressure that becomes your systolic reading. Between beats, your heart relaxes and refills with blood—this phase is called diastole. Diastolic blood pressure measures the force against your artery walls during this resting phase.

Think of your cardiovascular system like plumbing under pressure. Systolic pressure is the surge when the pump activates; diastolic pressure is the baseline pressure that remains in the pipes even when the pump is momentarily still. A healthy system maintains enough diastolic pressure to keep blood flowing to vital organs between heartbeats, but not so much that the arteries are under constant excessive stress.

The diastolic reading reflects several aspects of cardiovascular health: how well your blood vessels relax between beats, the resistance blood encounters as it flows through your arteries, and the overall flexibility and health of your arterial walls.

Diastolic Blood Pressure Ranges

Category	Diastolic Range	What It Means
Low	Below 60 mmHg	May cause symptoms; evaluate if symptomatic
Normal	60-79 mmHg	Healthy range—maintain lifestyle
Elevated risk	80-89 mmHg	Stage 1 hypertension; lifestyle changes recommended
High	90 mmHg or above	Stage 2 hypertension; likely needs treatment
Crisis	Above 120 mmHg	Medical emergency—seek immediate care

Remember that blood pressure classification considers whichever number places you in the higher category. If your systolic is 118 (normal) but your diastolic is 85 (stage 1 hypertension), your overall classification is stage 1 hypertension.

Why Diastolic Pressure Matters

For decades, medical professionals debated which number—systolic or diastolic—was more important. The pendulum swung toward emphasizing systolic pressure, particularly after research showed its strong connection to cardiovascular events in older adults. However, diastolic pressure remains critically important, especially in certain situations.

Diastolic Pressure and Heart Health

Your heart muscle receives its blood supply during diastole, not systole. When the heart contracts, it actually squeezes the coronary arteries that run through it, temporarily reducing blood flow. It's during the relaxation phase that blood flows freely into the heart muscle. Adequate diastolic pressure is essential for coronary blood flow and heart muscle health.

This creates an interesting paradox: while high diastolic pressure damages arteries and increases cardiovascular risk, very low diastolic pressure—especially in people with coronary artery disease—can also be problematic because it may reduce blood supply to the heart muscle.

Age-Related Patterns

Diastolic blood pressure follows a distinctive pattern as we age. It typically rises gradually through early adulthood, peaks around age 50-55, and then often begins to decline. This differs from systolic pressure, which tends to keep rising with age.

This divergence explains why isolated systolic hypertension—high systolic with normal or low diastolic—becomes so common in older adults. Arterial stiffening causes systolic pressure to rise while simultaneously allowing diastolic to fall, creating a widening "pulse pressure" (the gap between systolic and diastolic).

Younger Adults: Different Considerations

In younger adults (under 50), diastolic pressure may actually be a stronger predictor of cardiovascular risk than systolic. Isolated diastolic hypertension—where diastolic is elevated but systolic is normal—occurs more frequently in younger people and often relates to modifiable factors like obesity, physical inactivity, and excessive alcohol consumption.

This pattern matters because it means young people shouldn't dismiss elevated diastolic readings simply because their systolic looks fine. Both numbers warrant attention, and addressing elevated diastolic early can prevent progression to full hypertension.

High Diastolic Blood Pressure

What Causes Elevated Diastolic Pressure?

High diastolic pressure typically indicates increased resistance in the blood vessels—they're not relaxing as fully as they should between heartbeats. This can result from several factors:

Lifestyle factors play a significant role. Obesity increases blood volume and vascular resistance. High sodium intake causes fluid retention. Physical inactivity weakens cardiovascular fitness. Excessive alcohol consumption directly raises blood pressure. Chronic stress keeps the body in a state of heightened vascular tension.

Medical conditions can also elevate diastolic pressure. Kidney disease affects fluid balance and produces hormones that raise pressure. Thyroid disorders—both overactive and underactive—can affect blood pressure. Sleep apnea causes repeated nighttime stress responses that carry over into daytime pressure. Adrenal gland disorders may produce excess hormones that constrict blood vessels.

The Risks of High Diastolic Pressure

Sustained high diastolic pressure damages the cardiovascular system over time. It accelerates atherosclerosis (plaque buildup in arteries), increases heart attack and stroke risk, damages the kidneys' delicate blood vessels, and can harm the eyes and brain through effects on small blood vessels.

Lowering High Diastolic Pressure

The strategies for lowering diastolic blood pressure largely mirror those for lowering blood pressure overall:

Weight management is particularly effective. Losing even modest amounts of weight reduces vascular resistance and can noticeably lower diastolic readings.

Sodium reduction decreases fluid retention and vascular tension. Aim for less than 2,300 mg daily, ideally 1,500 mg if you have hypertension.

Regular exercise strengthens the heart and improves blood vessel flexibility. At least 150 minutes of moderate activity weekly is recommended.

Alcohol moderation can have rapid effects—reducing heavy drinking often produces measurable blood pressure improvements within weeks.

Stress management through exercise, meditation, adequate sleep, and healthy coping strategies helps reduce chronic vascular tension.

When lifestyle changes aren't sufficient, the same medications used for general hypertension—diuretics, ACE inhibitors, ARBs, calcium channel blockers, and beta blockers—effectively lower diastolic pressure as part of overall blood pressure reduction.

Low Diastolic Blood Pressure

While much attention focuses on high blood pressure, low diastolic pressure can also be problematic—and it's more common than many realize, particularly in older adults.

When Is Diastolic Too Low?

Diastolic blood pressure below 60 mmHg is generally considered low, though the threshold for concern depends partly on the individual. Some people naturally have lower diastolic pressures without symptoms or problems. Others experience symptoms even at levels some would consider normal.

What matters most is whether the low diastolic causes symptoms and whether it's creating problems with blood flow—particularly to the heart.

Symptoms of Low Diastolic Pressure

Low diastolic blood pressure may cause dizziness or lightheadedness (especially when standing), fatigue and weakness, difficulty concentrating, blurred vision, and in severe cases, fainting. These symptoms occur because organs—including the brain—may not receive optimal blood flow during the heart's resting phase.

The J-Curve Controversy

Research has identified what's called the "J-curve" relationship between diastolic blood pressure and cardiovascular events. Very high diastolic pressures clearly increase risk, but very low diastolic pressures (below 60-70 mmHg) may also be associated with increased cardiovascular events, particularly in people with existing coronary artery disease.

The likely explanation relates to coronary blood flow. If diastolic pressure falls too low, the heart muscle may not receive adequate blood supply during diastole, potentially triggering or worsening heart problems in vulnerable individuals.

This creates a treatment challenge: when treating high systolic pressure, lowering diastolic too much might cause harm. Modern treatment guidelines account for this by recommending careful monitoring and individualized targets, especially in older adults and those with heart disease.

Causes of Low Diastolic Pressure

Low diastolic pressure can result from dehydration, certain medications (including blood pressure medications, when doses are too aggressive), heart valve problems (particularly aortic valve regurgitation), and the natural stiffening of arteries that comes with age. Some people simply have naturally lower diastolic pressure as part of their individual physiology.

Measuring Diastolic Pressure Accurately

Accurate diastolic measurement follows the same principles as blood pressure measurement generally. The diastolic reading is recorded when the sounds of blood flowing through the artery disappear completely as the blood pressure cuff deflates. Modern automated monitors detect this automatically, but technique still matters.

For reliable readings, sit quietly for five minutes before measurement, avoid caffeine and exercise for 30 minutes beforehand, keep your arm supported at heart level, and sit with back supported and feet flat on the floor. Take multiple readings a minute apart and average them.

If your diastolic readings vary significantly from measurement to measurement, this might indicate measurement technique issues, or it could reflect genuine blood pressure variability worth discussing with your doctor.

Frequently Asked Questions