What is low blood pressure?

What is low blood pressure?

Lesley Dobson / 22 March 2017 ( 14 April 2021 )

Low blood pressure is when you have a blood pressure reading below what is regarded as normal. A normal reading is between 90/60mmHg and 140/90mmHg.

Low blood pressure is usually when you have a blood pressure of 90/60 or less.

A normal blood pressure reading is between 90/60mmHg and 140/90mmHg. Above this reading your blood pressure is high, and this puts you at greater risk of health problems.

To take just one example, high blood pressure is partially responsible for about half of the heart attacks and strokes that happen in the UK.

Low blood pressure is usually when you have a blood pressure of 90/60 or less. And, according to Blood Pressure UK, only one of the numbers has to be less than 90 or 60, for it to potentially count as low blood pressure.

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Low blood pressure is generally regarded as being better for your health, as it doesn’t cause the health problems that high blood pressure does. Low blood pressure is known as hypotension, while the term for high blood pressure is hypertension.

‘Low blood pressure is when it’s persistently below 90/60. It’s not as common as High BP and it’s not usually as detrimental, ‘ explains Julie Ward, senior cardiac nurse at the British Heart Foundation.

‘It’s usually related to something that’s going on at the time. If you’ve been out in the heat and haven’t drunk enough fluids, you may have dehydration. Or you may not have enough fluid, or may have an infection, such as a urinary tract or a chest infection.’

‘Low blood pressure is not actually a problem, unless a person feels faint, or dizzy, or generally unwell with it. It’s not usually a disease, it’s something that normally happens as a result of something else. In these cases low blood pressure definitely needs addressing. See your GP, to find out what’s causing it. It’s usually a temporary situation, and a symptom of something else.’

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How is blood pressure measured?

Blood pressure is usually measured by a nurse or a doctor using a piece of equipment called a sphygmomanometer. You will have a fabric cuff wrapped around your upper arm to start with. Then the control box that shows your blood pressure readings will be turned on, pumping air into the cuff. As this happens you’ll feel the cuff becoming tighter around your upper arm.

The sphygmomanometer will show your blood pressure reading on a small screen that is part of the equipment. Your nurse or doctor may take more than one reading, to double check the results, particularly if they are higher or lower than the ideal readings. These are between 90/60mmHg and 120/80mmHg.

Systolic and diastolic: what do the two blood pressure numbers mean?

Sometimes you may have your blood pressure checked using an older monitor. These work in a similar way, but they aren’t electronic and don’t have a digital display to show your blood pressure readings. Instead, the nurse or doctor will pump the cuff up by hand, and will use a stethoscope to listen to your pulse.

How to monitor your blood pressure

What causes low blood pressure?

Low blood pressure is something that can happen naturally – it is just how your body works, and may even be an inherited trait.

However, some people have low blood pressure because they have specific health issues, such as heart problems – a very low heart rate (bradycardia), heart failure, severe allergic reactions (anaphylaxis), and anaemia, where your body is deficient in red blood cells. It can also happen if you take particular medicines.

Factors that may cause low blood pressure

You are more likely to have a low blood pressure reading if:

you are relaxed,
have recently eaten (a portion of your blood supply will be busy helping you digest your food)
warmth may also send your blood pressure down
being someone who is generally relaxed, rather than stressed, may help to keep your blood pressure low

Medicines that reduce blood pressure

Some medicines may reduce your blood pressure. These include:

ACE (angiotensin-converting enzyme) inhibitors
alpha-blockers (drugs designed to lower blood pressure)
diuretics (also known as ‘water pills’), that help you pass excess water and salt (as urine) out of your body

Symptoms of low blood pressure

You may not be aware that you have low blood pressure most of the time, if this is something that has happened naturally. There are times, however, when your blood pressure can drop to the point where it does start to affect you.

You need to have enough blood supplying important parts of your body, such as your heart and brain, to keep everything functioning properly. In some cases, when your blood pressure drops lower than normal, you may feel dizzy or faint. If this does happen, make sure that you sit down, somewhere safe, until the dizziness passes.

Dizziness: symptoms, causes and treatments

Feeling dizzy or faint can also be the result of a condition called orthostatic hypotension. This is when your blood pressure drops suddenly when you stand up after you’ve been sitting or lying down. It may also happen when you get out of bed first thing in the morning.

If this happens, sit down again, carefully, and wait until the feeling that you might faint has passed. You should feel better after a few seconds. If this keeps happening, talk to your GP, in case the problem is being caused by your medication, or you have anaemia, that might need treatment.

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