High diastolic blood pressure: why is my bottom number high?

A high bottom number with a normal top number is common, especially before about 55. It's rarely an emergency, but it shouldn't be ignored either. Here's what counts as high, what the research says about the risk, and what actually brings it down.

Published November 1, 2026 · Based on the 2025 AHA/ACC high blood pressure guideline

What counts as a high bottom number?

The bottom number, or diastolic pressure, is the pressure in your arteries while your heart rests between beats. Under the 2025 American Heart Association and American College of Cardiology guideline:

If your two numbers fall in different categories, the higher one counts. So 118/85 is stage 1, even though 118 on its own would be normal. When only the bottom number is high, it's called isolated diastolic hypertension.

Not every country draws the line at 80. European and UK guidelines start at 140/90 for clinic readings, so a reading of 118/85 may be called high in the US but not diagnosed as hypertension in Europe. To check any reading, use our blood pressure reading checker.

First, check the reading is real

One high number doesn't mean you have high blood pressure. Before you worry, rule out the things that push a reading up:

• Talking can raise both numbers by around 10 points.
• An unsupported back or dangling feet can add about 6 points.
• The wrong cuff or a badly placed arm. A cuff that doesn't fit, or an arm resting below heart level, can throw off a reading.
• A rushed measurement. Sit quietly for 5 minutes first, with an empty bladder and no coffee, exercise or smoking in the previous 30 minutes.

Then look at your average. Our guide to measuring at home explains the 7-day routine, which tells you far more than any single reading.

Why the bottom number goes up

Experts don't fully understand why the bottom number sometimes rises on its own. It's most common in people younger than about 55. Later in life the pattern often flips, with the top number climbing while the bottom number levels off or falls. Cleveland Clinic names three of the biggest risk factors:

• Overweight or obesity
• Sleep apnea. If you snore loudly, wake up tired or someone has noticed you stop breathing at night, mention it to your doctor.
• Smoking

Heavy drinking and a salty diet raise blood pressure too, and your doctor may also check whether another condition is behind it.

How serious is it?

The risk seems to depend on how high the number is.

That's not an all-clear, for three reasons:

• It can be an early sign. People with a high bottom number were more likely to develop a high top number later, which is why the authors of that eight-study analysis recommend follow-up.
• Younger adults are a gap. Those results may not apply to people under 40, who haven't been studied as closely.
• Both numbers still count. In 1.3 million adults, high systolic and high diastolic pressure each predicted heart attack and stroke, though the top number had the bigger effect.

So a home average of 82 is a reason to act on your habits and keep measuring, not a reason to panic. A steady average of 90 or more is a reason to book an appointment.

How to lower diastolic blood pressure

No habit targets the bottom number alone. What lowers blood pressure in general tends to lower both numbers:

• Lose weight, if you're carrying extra. It's one of the main risk factors above.
• Eat less salt. In a controlled feeding trial, people over 45 without high blood pressure who cut salt from a high to a low level on a typical US diet saw an average drop of 7 points in the top number and about 4 in the bottom.
• Try the DASH diet. It's rich in vegetables, fruit and low-fat dairy. The same trial found the combination of DASH and less salt worked best.
• Drink less. Cutting back made the biggest difference in heavy drinkers: people having six or more drinks a day who halved their intake lowered their bottom number by about 4 points. Among people having two drinks a day or fewer, cutting back made no significant difference.
• Move more. Aim for at least 150 minutes of aerobic exercise a week.
• Stop smoking, and get sleep apnea checked and treated if it's suspected.

Will you need medication? Many people with isolated diastolic hypertension don't, at least not right away. Your doctor may suggest it if the bottom number stays high, the top number starts rising, or you have a condition such as diabetes or kidney disease. In a 2026 analysis of 51 clinical trials, blood pressure medication lowered cardiovascular risk about as much in people with isolated diastolic hypertension as in everyone else, though the result for that smaller group alone fell just short of statistical significance. That decision depends on your overall risk, so it's one to make with your doctor. Blood pressure medicine lowers both numbers, and there isn't one that only treats the bottom one.

Track both numbers at home

Since a high bottom number can come before a high top number, the useful thing to watch is how your average changes over time:

1. Measure morning and evening for 7 days, two readings each time.
2. Leave out day 1, and average the rest for each number separately.
3. Repeat after a few months, or after any change to your habits or medication.

Our free printable log has a row for every reading and a box for the average, or you can keep it on an iPhone with the app above. Either way, take it with you: a doctor can do much more with a week of readings than with one number from memory.

Common questions

Is a diastolic of 85 bad?

As a home average, 85 is stage 1 in the US and worth working on through your habits. On its own, with a normal top number, it isn't an emergency. Mention it at your next appointment, sooner if you have diabetes, kidney disease or a history of heart problems.

Is a diastolic of 100 dangerous?

If it's a repeated average, that's stage 2, so see your doctor soon rather than waiting for a routine visit. Measure again first if it's a single reading. If it's above 120, see when to get help.

Why is my bottom number high but my top number normal?

It's a common pattern, particularly under about 55. Overweight, sleep apnea and smoking are among the biggest risk factors, though often no single cause is found. First make sure your measuring technique isn't the reason.

Is stress the cause?

Stress can raise blood pressure for a while, which is one reason a single reading can mislead. If your average stays high over a week of calm, seated readings, don't put it down to stress alone.

What if my bottom number is low?

A low bottom number with a high top number is a different pattern, more common in older adults. See normal blood pressure for older adults. If it comes with dizziness or fainting, contact your doctor.

When to get help

If your bottom number is above 120 or your top number is above 180, wait a minute and measure again. If it's still that high and you have chest pain, shortness of breath, back pain, numbness or weakness, a change in vision or difficulty speaking, call 911 or your local emergency number. Without symptoms, contact your doctor the same day.

Sources

• American Heart Association and American College of Cardiology: 2025 guideline for high blood pressure in adults
• American Heart Association: Understanding blood pressure readings
• Cleveland Clinic: Isolated diastolic hypertension
• Jacobsen AP, et al. European Heart Journal, 2021: Cohort study and meta-analysis of isolated diastolic hypertension
• McGrath BP, et al. Hypertension, 2020: Isolated diastolic hypertension in the UK Biobank
• Flint AC, et al. New England Journal of Medicine, 2019: Effect of systolic and diastolic blood pressure on cardiovascular outcomes
• Bidel Z, et al. European Heart Journal, 2026: Blood pressure lowering in isolated diastolic hypertension and cardiovascular risk
• Vollmer WM, et al. Annals of Internal Medicine, 2001: Effects of diet and sodium intake on blood pressure (DASH-Sodium subgroups)
• Roerecke M, et al. Lancet Public Health, 2017: The effect of a reduction in alcohol consumption on blood pressure
• American Medical Association: 4 big ways blood pressure measurement goes wrong
• StatPearls: Blood pressure measurement