A low bottom blood pressure number, called diastolic pressure, usually results from age-related stiffening of arteries, medications, or an underlying health condition. Doctors generally consider a diastolic reading below 60 mmHg to be low, especially when your top (systolic) number stays at 100 mmHg or above. This pattern, known as isolated diastolic hypotension, becomes increasingly common after age 50 and deserves attention because it can affect how well your heart muscle receives blood.
What the Bottom Number Actually Measures
Your blood pressure reading has two numbers. The top number (systolic) captures the force when your heart pumps. The bottom number (diastolic) measures the pressure in your arteries between beats, when your heart is relaxing and refilling with blood. Think of it as the baseline pressure your blood vessels maintain while your heart rests.
This resting pressure matters more than most people realize. Your heart muscle gets its own blood supply almost entirely during the relaxation phase between beats, not during the pumping phase. When your heart contracts, it actually squeezes shut the small arteries running through its muscle, blocking its own blood flow. So the diastolic pressure is what drives oxygen-rich blood into your heart tissue. When that pressure drops too low, your heart may not get the oxygen it needs, particularly if you already have narrowed coronary arteries or other cardiovascular issues.
Why Diastolic Pressure Drops With Age
The most common reason for a low bottom number is simply getting older. After about age 50, diastolic pressure tends to decline while systolic pressure continues to rise. The explanation is straightforward: your arteries lose elasticity over time. Healthy, flexible arteries stretch when the heart pumps blood into them, then spring back between beats like a rubber band, maintaining pressure in the system. As arteries stiffen from years of wear, calcification, and the natural breakdown of elastic fibers in vessel walls, they expand less with each heartbeat and have a harder time snapping back. The result is higher pressure during the pump (systolic goes up) and lower pressure between beats (diastolic goes down).
This creates what’s called a wide pulse pressure, meaning a large gap between your two numbers. Someone might have a reading of 150/60, for example. The gap between those numbers is the pulse pressure (90 mmHg in this case), and a wider gap generally reflects stiffer arteries. In the Framingham Heart Study, researchers found that the combination of a pulse pressure of 68 mmHg or higher with a diastolic pressure below 70 mmHg carried the highest risk of cardiovascular events.
Medications That Lower Diastolic Pressure
Blood pressure medications are a leading cause of low diastolic readings, which creates an ironic problem: treating high systolic pressure can push the bottom number too low. Several drug classes contribute to this.
- Diuretics (water pills) reduce blood volume by increasing urine output, which can lower both numbers but may disproportionately drop diastolic pressure.
- Alpha-blockers relax blood vessel walls, reducing the resistance that maintains diastolic pressure between heartbeats.
- Beta-blockers slow the heart rate and interfere with the body’s ability to tighten blood vessels when you stand up.
- Nitrates relax veins, reducing the amount of blood returning to the heart and lowering overall pressure.
Non-cardiovascular medications can do it too. Antidepressants (especially older tricyclics, but also SSRIs), antipsychotics, benzodiazepines, opioids, and Parkinson’s medications all have mechanisms that lower blood pressure. If you’ve noticed your bottom number dropping after starting a new medication, the timing is probably not a coincidence.
Health Conditions That Play a Role
Several medical conditions can push diastolic pressure down. Heart valve problems, particularly a leaky aortic valve, allow blood to flow backward into the heart during the resting phase, directly reducing diastolic pressure. Heart failure and a history of heart attack are both associated with lower diastolic readings. Diabetes contributes through a different pathway: chronically elevated blood sugar promotes inflammation that damages and remodels blood vessel walls, making them stiffer and less able to maintain pressure between beats.
Dehydration lowers blood volume, which reduces pressure throughout the system. Severe cases from prolonged vomiting, diarrhea, or heavy sweating can cause a noticeable drop. Hormonal conditions that affect the glands regulating blood pressure, including adrenal insufficiency and thyroid disorders, can also be involved. In older adults, some research suggests that frailty itself may show up as low diastolic pressure, making it both a cause and a marker of declining health.
Symptoms You Might Notice
Many people with mildly low diastolic pressure feel nothing at all and only discover it during a routine check. When the drop is more significant, symptoms tend to reflect reduced blood flow to the brain and other organs: lightheadedness or dizziness (especially when standing up), fatigue that doesn’t improve with rest, blurred vision, and difficulty concentrating. Some people feel faint or unsteady, particularly after meals, when blood diverts to the digestive system and diastolic pressure can dip further. This post-meal blood pressure drop is most common in older adults.
If you’re experiencing these symptoms alongside a diastolic reading consistently below 60 mmHg, the low pressure is the likely culprit rather than something to dismiss.
Why a Low Bottom Number Raises Heart Risk
The concern with persistently low diastolic pressure goes beyond uncomfortable symptoms. Data from the Framingham Heart Study found that people with diastolic pressure below 70 mmHg who had already experienced a cardiovascular event were significantly more likely to have another one. Among those on blood pressure treatment, the risk of a recurrent event was about five times higher compared to those with diastolic readings between 70 and 89 mmHg. For untreated individuals, the risk was nearly twelve times higher. Heart disease, heart failure, and stroke were all individually more common in the low diastolic group.
A large analysis using national health data found that diastolic pressure below 60 mmHg was associated with increased risk of death from all causes, even when the systolic number looked normal. The mechanism ties back to coronary perfusion: when diastolic pressure is too low, the driving force that pushes blood into the heart’s own arteries weakens. Over time, especially in someone with partially blocked coronary arteries, this can starve the heart muscle of oxygen.
What You Can Do About It
Managing a low diastolic number depends on what’s causing it. If medications are the issue, adjusting doses or switching drug classes can help, but this requires working with whoever prescribes them rather than making changes on your own.
For lifestyle approaches, staying well hydrated is the simplest and most effective step. Water increases blood volume, which supports pressure in the system. Alcohol works in the opposite direction, lowering blood pressure even in moderate amounts, so cutting back can make a measurable difference. Increasing salt intake may help raise blood pressure, though this advice is the reverse of what most people hear. It needs to be done carefully, since too much sodium can strain the heart, especially in older adults.
Compression stockings are a practical tool that many people overlook. They apply gentle pressure to the legs, preventing blood from pooling in the lower body and helping more of it circulate back to the heart. This is particularly useful if you notice symptoms when standing for long periods. Standing up slowly, avoiding prolonged hot showers, and eating smaller, more frequent meals can also help blunt the dips in pressure that trigger dizziness and lightheadedness.
Tracking your readings at home gives you and your healthcare provider a clearer picture than occasional office visits. Note the time of day, whether you’ve eaten recently, and any symptoms. A pattern of diastolic readings consistently below 60 mmHg, especially paired with a systolic number above 130 or 140, is worth a focused conversation about whether your current treatment plan needs adjusting.