When you get your blood pressure checked, the result is given as two numbers (e.g., 120/80 mmHg). These numbers measure the force of blood against your artery walls during two different stages of your heartbeat.
Understanding the difference between systolic and diastolic pressure is the first step in managing your cardiovascular health.
The systolic number (the higher value) measures the pressure in your arteries when your heart muscle contracts and pumps oxygen-rich blood out to your body.
What it represents: The maximum pressure exerted on your artery walls.
Why it matters: Doctors pay close attention to this number because a high systolic reading often indicates arterial stiffness or that your heart is working too hard. It is a major risk factor for heart disease and stroke, especially as we age.
The diastolic number (the lower value) measures the pressure in your arteries when your heart rests between beats.
What it represents: The minimum “resting” pressure in your circulatory system.
Why it matters: A high diastolic reading suggests your blood vessels aren’t relaxing properly between beats, which can put a constant, underlying strain on your heart.
Whilst ‘normal’ can vary based on age, gender, and pregnancy status, most doctors use the following categories for adults:
| Blood Pressure Category | Systolic (Top) | Diastolic (Bottom) | |
| Low Blood Pressure | Under 90 | and/or | Under 60 |
| Normal | 90 – 120 | and | 60 – 80 |
| Elevated (Pre-high) | 121 – 139 | or | 81 – 89 |
| High (Hypertension) | 140 or over | or | 90 or over |
Note: In the elderly, a reading of 140/90 may be considered acceptable, whereas during pregnancy, readings often drop below 100/70. Always consult your GP to determine your personal “optimal” target.
Is the top or bottom number more important?
Both are vital. However, for people over 50, the systolic (top) number is often a more accurate predictor of heart attack and stroke risk. For younger individuals, a high diastolic (bottom) number can be an early warning sign of future hypertension.
What if only one number is high?
This is known as Isolated Hypertension. Whether it is just the top or just the bottom number that is elevated, the risk to your long-term health remains the same, and it should be discussed with a healthcare professional.
Blood pressure is a dynamic parameter. It reacts to stress, caffeine, exercise, and even how you are sitting. This is why doctors look for trends over time rather than a single “one-off” reading.
Low: <90/60 mmHg
Ideal: Between 90/60 and 130/80 mmHg
High: >140/90 mmHg
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