A high diastolic blood pressure reading, the bottom number on your blood pressure result, means the pressure in your arteries stays elevated between heartbeats. Under current guidelines, a diastolic reading of 80 mm Hg or higher puts you in the hypertension range, even if your top number looks normal. This matters because elevated diastolic pressure independently raises your risk of heart attack, stroke, and cardiovascular death.
What Counts as High Diastolic Pressure
The 2025 guidelines from the American Heart Association and American College of Cardiology define blood pressure categories using both the systolic (top) and diastolic (bottom) numbers. Either number alone can qualify you for a diagnosis:
- Normal: below 120/80 mm Hg
- Elevated: 120 to 129 systolic with diastolic still below 80
- Stage 1 hypertension: 130 to 139 systolic or 80 to 89 diastolic
- Stage 2 hypertension: 140 or higher systolic or 90 or higher diastolic
So a reading of, say, 118/86 would be classified as Stage 1 hypertension based on the diastolic number alone. This pattern, where only the bottom number is high, is called isolated diastolic hypertension. When the 2017 guidelines lowered the threshold from 90 to 80 mm Hg, roughly 12 million more U.S. adults were reclassified as hypertensive.
Why Diastolic Pressure Rises
Diastolic pressure reflects what’s happening in your blood vessels during the brief pause between heartbeats. It’s driven mainly by two factors: how much blood your heart pumps and how much resistance your smaller arteries create. When those small vessels are stiff or constricted, blood has nowhere to go easily, and the pressure stays high even while the heart relaxes.
Cholesterol levels and insulin resistance appear to play a direct role. Research from the American Heart Association found that both were independently linked to diastolic pressure increases, more so than age, body weight, or fitness level. This makes sense: cholesterol buildup narrows arteries, and insulin resistance impairs blood vessels’ ability to relax and widen properly.
What Causes It
For most people, high diastolic pressure results from the same combination of genetics, diet, physical inactivity, and excess weight that drives high blood pressure in general. But several specific medical conditions can push diastolic readings up:
- Kidney disease: The kidneys regulate fluid balance and blood pressure. Conditions like diabetic kidney damage, polycystic kidney disease, or inflammation of the kidney’s filtering units can raise pressure by retaining sodium and water.
- Sleep apnea: Repeated breathing interruptions during sleep deprive the body of oxygen. Over time, this damages blood vessel walls and triggers the nervous system to release chemicals that raise blood pressure.
- Narrowed kidney arteries: Fatty plaque buildup in the arteries feeding your kidneys tricks them into thinking blood flow is low, which triggers hormones that tighten blood vessels body-wide.
- Hormonal disorders: Conditions like aldosteronism, where the adrenal glands produce excess aldosterone, cause the body to retain salt and water. Cushing syndrome, involving excess cortisol, also raises pressure.
- Thyroid problems: An underactive thyroid can increase vascular resistance, while an overactive thyroid increases the heart’s output.
If your diastolic pressure is high and doesn’t respond well to typical treatments, your doctor may investigate these secondary causes.
The Cardiovascular Risks
A persistently elevated diastolic reading is not a harmless quirk. Studies tracking patients over time found that elevated diastolic pressure was associated with a 42% higher risk of cardiovascular death, a 19% higher risk of stroke, and a 14% higher risk of the combined outcome of cardiovascular death, heart attack, or stroke. These risks held even when systolic pressure was under control.
At the extreme end, a diastolic reading above 120 mm Hg (along with systolic above 180) qualifies as a hypertensive crisis. Symptoms at that level can include severe headache, vision changes, chest pain, and shortness of breath. This requires immediate medical attention because it can damage the brain, heart, and kidneys within hours.
How Age Changes the Pattern
High diastolic pressure is more common in younger and middle-aged adults. Population data show that both systolic and diastolic pressure rise steadily until around age 60. After that, something shifts: systolic pressure keeps climbing, but diastolic pressure plateaus and often drops.
The reason is arterial stiffness. As large arteries lose their elasticity with age, they absorb less of the force from each heartbeat. This pushes systolic pressure higher while actually reducing diastolic pressure for a given level of blood flow. So if you’re under 50 with a high diastolic reading, it likely reflects increased resistance in your smaller blood vessels. If you’re over 65, your doctor is probably more focused on your systolic number, since diastolic hypertension naturally becomes less common with aging.
Make Sure Your Reading Is Accurate
Before worrying about a single high reading, consider whether it was measured correctly. Blood pressure cuff size is one of the most common sources of error. A cuff that’s too narrow for your arm inflates around a smaller area and produces falsely high readings. Research has shown that standard one-size cuffs fail accuracy standards for diastolic pressure on both small and large arms. If your arm circumference is larger or smaller than average, ask for an appropriately sized cuff.
Other factors that inflate readings include caffeine or exercise within 30 minutes, a full bladder, crossed legs, talking during the measurement, or resting your arm below heart level. A single elevated reading doesn’t confirm hypertension. The diagnosis typically requires elevated readings on at least two separate occasions.
Lifestyle Changes That Lower Diastolic Pressure
Diet has a meaningful effect. The DASH eating pattern, which emphasizes fruits, vegetables, whole grains, and low-fat dairy while limiting saturated fat, reduces diastolic pressure by about 3 mm Hg on average. That may sound modest, but at a population level, even small reductions translate to fewer strokes and heart attacks over time. Interestingly, simply cutting sodium alone has a less clear effect on diastolic pressure. A review of long-term trials found sodium restriction lowered systolic pressure by about 1 mm Hg but had no significant effect on diastolic. The combination of lower sodium with an overall healthier dietary pattern seems to be what moves the needle.
Regular aerobic exercise, maintaining a healthy weight, limiting alcohol, and managing stress all contribute as well. For people with high diastolic readings driven by insulin resistance and cholesterol, these lifestyle shifts address the root cause rather than just the number on the monitor.
When Medication Is Needed
If lifestyle changes aren’t enough and your diastolic pressure stays at 90 or above, medication is generally recommended. For readings between 80 and 89, the decision depends on your overall cardiovascular risk, including factors like diabetes, kidney disease, or existing heart problems.
Four main classes of blood pressure medication are used as first-line treatment. Each lowers diastolic pressure by roughly 4 to 5 mm Hg on average, though individual responses vary. These medications work through different mechanisms: some relax blood vessels, some reduce fluid volume, and others slow the heart rate or block hormones that tighten arteries. Your doctor will choose based on your age, other health conditions, and how you respond. If one medication at a standard dose doesn’t bring your numbers into range, a combination of two medications from different classes is common.
One important note: thiazide-type diuretics, one of the most commonly prescribed blood pressure medications, tend to have a stronger effect on systolic than diastolic pressure. If your diastolic number is the primary concern, your doctor may lean toward a different class or a combination approach.