You’ve probably sat in that crinkly paper-covered chair at the doctor's office, felt the squeeze of the cuff, and heard the nurse rattle off two numbers. Maybe it was 120 over 80. Or 138 over 92. Most of us focus on that big first number—the systolic—because it feels like the "main" one. But if you’re wondering what is the bottom number of blood pressure, you’re actually asking about the part of the cycle where your heart is supposed to be relaxing.
It’s called diastolic pressure.
Basically, while the top number measures the force of blood against your artery walls when your heart beats, the bottom number is the pressure in those same arteries when your heart is resting between those beats. It’s the "off" beat. But don’t let the word "rest" fool you. That number tells a huge story about the health of your blood vessels and how hard your heart has to work even when it isn't actively pumping.
The Bottom Number of Blood Pressure Explained Simply
So, what’s actually happening down there?
Think of your circulatory system like the plumbing in an old house. When the pump is on, the pressure is high. When the pump pauses, the pressure drops, but it shouldn't drop to zero. If it did, your blood would stop moving. Your arteries have a natural elasticity that keeps a baseline level of pressure going so that oxygen still reaches your organs.
According to the latest 2025-2026 guidelines from the American Heart Association (AHA) and the American College of Cardiology (ACC), that bottom number should ideally be less than 80.
If it's consistently hitting 80 or 89, you're in Stage 1 Hypertension territory. If it crosses 90, you're looking at Stage 2. Honestly, many people walk around with a normal top number and a high bottom number (this is called isolated diastolic hypertension), and they have no idea they’re at risk.
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Why doctors used to ignore it (and why they don't now)
For a long time, the medical community was obsessed with the top number. The thinking was that as we age, the systolic pressure is a better predictor of strokes and heart attacks. And that's still mostly true for older adults.
However, recent research—including a massive study published in the New England Journal of Medicine—has shown that the diastolic number is a major "red flag" for younger adults. If you're under 50, that bottom number might actually be a better predictor of your future heart health than the top one.
What Does a High Bottom Number Mean?
When that bottom number starts creeping up into the 80s and 90s, it usually means your arteries are losing their "stretch."
They’re becoming stiffer.
When your heart tries to rest, the blood is still pushing too hard against the vessel walls. This can be caused by a bunch of stuff:
- Too much salt: Sodium makes your body hold onto water, which increases the volume of blood in your pipes.
- Stress: It’s not just a cliché; chronic stress keeps your blood vessels constricted.
- Alcohol: Even a couple of drinks can cause that bottom number to spike the next day.
- Lack of sleep: Your blood pressure is supposed to "dip" at night. If you aren't sleeping well, it stays high.
Dr. Michael Hecht Olsen, a prominent researcher in cardiovascular prevention, has pointed out that for people under 50, diastolic readings provide "additional prognostic predictive information." In plain English? If your bottom number is high, your heart is never truly getting a break.
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The Danger of "The Gap"
There is also something called Pulse Pressure. This is the mathematical difference between your top and bottom numbers. If your top number is 150 and your bottom is 70, that’s a gap of 80. A wide gap like that often points to very stiff, aged arteries, which is its own kind of trouble.
Can the Bottom Number Be Too Low?
Yes. And it's kinda scary.
While we spend all our time worrying about high blood pressure, isolated diastolic hypotension—where the bottom number is too low (usually below 60)—is a real problem, especially for seniors.
Your heart muscle is unique. Unlike the rest of your body, which gets its blood supply when the heart pumps, the heart’s own coronary arteries actually fill up during the "rest" phase (diastole).
If the bottom number of blood pressure is too low, your heart might not be getting enough oxygen for itself. This can lead to:
- Dizziness or "room-spinning" when you stand up.
- Fatigue that doesn't go away with rest.
- An increased risk of falls.
- Potential heart failure over long periods because the heart muscle is "starving" for blood.
Often, this happens because of over-medication. A doctor might be trying so hard to get your top number down that the bottom number sinks like a stone. It’s a delicate balancing act.
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Real-World Ways to Fix the Numbers
If you've checked your stats and realized your bottom number is acting up, don't panic. You can actually move the needle quite a bit with lifestyle tweaks that aren't just "eat more kale."
Fix Your Potassium-to-Sodium Ratio
Most people focus on "low salt." That’s fine, but it’s only half the battle. You need potassium to help your kidneys flush that salt out. Reach for bananas, sure, but also avocados, potatoes (with the skin!), and spinach. It’s about the balance, not just the deprivation.
The "Dipping" Factor
Your blood pressure should naturally drop by 10% to 20% while you sleep. If you have sleep apnea—where you stop breathing periodically at night—your body stays in "fight or flight" mode. This keeps the bottom number of blood pressure high 24/7. If you snore or wake up tired, getting a sleep study might do more for your blood pressure than any pill.
Grip Training?
Surprisingly, some studies have shown that isometric handgrip exercises—basically squeezing a stress ball or a dedicated grip strengthener for a few minutes a day—can specifically help lower diastolic blood pressure. It’s a weirdly effective trick for such a small movement.
Taking Action Today
Knowing what is the bottom number of blood pressure is the first step, but the second is getting an accurate reading. Most people mess this up at home.
To get a real number, you've gotta sit still. No talking. No scrolling on your phone. Feet flat on the floor—crossing your legs can actually boost your diastolic number by 5 to 10 points instantly. Take two or three readings a minute apart and average them out.
If that bottom number is consistently over 80, it’s time to have a real conversation with a professional. They might use the new PREVENT™ risk calculator (the 2026 gold standard) to see what your 10-year risk looks like.
Next Steps for Your Health:
- Track your trends: Don't rely on one "white coat" reading at the doctor; log your numbers at home for one week, twice a day.
- Check your meds: If your bottom number is below 60 and you feel dizzy, ask your doctor if your current dosage is too aggressive.
- Audit your salt: Look at the labels on "healthy" frozen meals; they are often hidden sodium bombs that target your diastolic pressure specifically.
- Prioritize Sleep: Aim for 7-9 hours of quality rest to ensure your blood pressure "dips" correctly at night.