Blood Pressure (low)

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Introduction

Introduction

Low blood pressure, also known as hypotension, is where blood pressure in your arteries is abnormally low.

Naturally low blood pressure is unlikely to cause any symptoms and is normally nothing to worry about.

But if your blood pressure drops too low, it can restrict the amount of blood flowing to your brain and other vital organs, which can cause unsteadiness, dizziness or fainting.

See your GP if you experience any symptoms of low blood pressure and are concerned.

All adults should have their blood pressure checked at least every five years. If you haven't had yours measured or don't know what your reading is, ask your GP to check it.

Read more about the symptoms of low blood pressure.

What is low blood pressure?

The heart pumps a constant supply of blood around the body through arteries, veins and capillaries. Blood pressure is a measure of the force of the blood on the walls of the arteries as the blood flows through them.

It's measured in millimetres of mercury (mmHg) and recorded as two measurements:

  • systolic pressure - the pressure when your heart beats and squeezes blood into your arteries
  • diastolic pressure - the pressure when your heart rests between beats 

For example, if your systolic blood pressure is 120mmHg and your diastolic blood pressure is 80mmHg, your blood pressure is 120 over 80, which is commonly written as 120/80.

Normal blood pressure is between 90/60 and 140/90. If you have a reading of 140/90 or more, you have high blood pressure (hypertension). This puts you at greater risk of developing serious health conditions, such as heart attack or stroke.

People with a blood pressure reading under 90/60 are usually regarded as having low blood pressure.

Read more about diagnosing low blood pressure.

Why do I have low blood pressure?

You can have low blood pressure for many reasons, including the time of day, your age, the temperature, any medication you may be on, an injury, and some illnesses.

Read more about the causes of low blood pressure.

Treatment and self-help

Naturally low blood pressure doesn't usually need to be treated unless it's causing symptoms such as dizziness or recurrent falls. If it's causing symptoms, your GP will look at what the cause might be in case it can be treated.

There are also various things you can do to help limit symptoms of low blood pressure, including:

  • standing up gradually and avoiding standing for long periods of time
  • ensuring you are well hydrated
  • wearing support stockings
  • adding more salt to your diet
  • eating smaller meals more often

Read more about treating low blood pressure.

Symptoms of low blood pressure

Symptoms of low blood pressure

If your blood pressure is naturally low, it's unlikely to cause any symptoms or require treatment.

However, low blood pressure can sometimes mean there's not enough blood flowing to your brain and other vital organs, which can lead to symptoms such as:

What to do if you have symptoms

If you think you may be experiencing an episode of low blood pressure, you should:

  • stop what you're doing
  • sit or lie down
  • drink some water

The symptoms will usually pass after a few seconds or minutes.

When to see your GP

You should see your GP if you have frequent symptoms of low blood pressure. Your GP can measure your blood pressure and help identify any underlying causes of the problem.

Read more about diagnosing low blood pressure.

Low blood pressure after suddenly standing up

If you experience symptoms of low pressure after changing positions, such as standing up, it's known as postural, or orthostatic, hypotension.

Symptoms shouldn't last longer than a few seconds, as your blood pressure will adjust to your new position.

This type of low blood pressure tends to affect people more as they get older, when it can lead to more frequent falls. Similar symptoms may also occur after exercise.

Low blood pressure after eating

If you experience symptoms after eating, it's known as postprandial hypotension. It occurs more often in older people, particularly in those who have high blood pressure or conditions such as Parkinson's disease and diabetes mellitus.

After a meal, your intestines need a large amount of blood for digestion. If your heart rate doesn't increase enough to maintain blood pressure, your blood pressure will fall, causing symptoms.

Low blood pressure after standing for long periods

Some people experience symptoms after standing up for long periods of time. This is sometimes known as neutrally mediated hypotension, and most often affects children and young adults.

Read more about the causes of low blood pressure.

Causes of low blood pressure

Causes of low blood pressure

Low blood pressure (hypotension) has many possible causes, from lifestyle choices, to medication or an underlying health condition.

In some cases, it may just be the result of being healthy and active or a tendency you've inherited from your parents.

Throughout the day, it's normal for your blood pressure to vary depending on what you're doing. Stress at work, the temperature outside and your diet could all affect your blood pressure reading.

This is why it's important your blood pressure is checked under similar conditions each time to ensure results are consistent.

If your blood pressure reading is low, your GP will first consider whether it has been affected by:

  • the time of day - blood pressure is normally lower overnight while you're sleeping, rises a few hours before you wake up, and continues to rise during the day, reaching its highest mid-afternoon
  • how stressed or relaxed you are - you have lower blood pressure the more relaxed you are
  • how much exercise you do - initially, exercise will raise your blood pressure, but if you're healthy and exercise regularly, your blood pressure will be low when you're resting
  • temperature - a warm temperature may cause your blood pressure to fall
  • if you have recently eaten - blood is diverted to the gut when food needs to be digested, so the blood pressure elsewhere in your body falls

If your blood pressure is still considered low after taking these factors into account, there may be another cause. Some possibilities are explained below.

Genes

Some research has suggested low blood pressure is genetic. If your parents have low blood pressure, it's possible you could inherit it from them.

Age

Your blood pressure usually increases as you get older, but a drop in blood pressure from movement or eating is more common with age.

Medication

Some types of medication may cause low blood pressure, including the following:

  • beta-blockers - a medicine that may be prescribed for a problem with your heart
  • angiotensin-converting enzyme (ACE) inhibitors
  • angiotensin receptor blockers
  • alpha-blockers - medicine prescribed to lower blood pressure for people with high blood pressure (hypertension) and men with prostate gland problems
  • diuretics (water tablets)
  • some antidepressants

Your GP will discuss possible side effects with you when prescribing medication, and your blood pressure will be carefully monitored if you're considered to be at risk of hypotension.

Dehydration

Dehydration can occur if fluid is lost, either through skin from excessive sweating in hot weather, or from the gastrointestinal tract as a result of vomiting or diarrhoea.

An illness or underlying health condition

Examples of conditions and illnesses that can lead to low blood pressure are given below. Prolonged bed rest can also lower blood pressure.

Anaemia

Low blood pressure can sometimes be caused by anaemia, where the amount of haemoglobin in the blood is below the normal level or there are fewer red blood cells than normal.

Heart condition

A heart condition, such as heart disease or a heart attack, can cause low blood pressure because your heart may not be able to pump blood around your body.

Neurological disorder

Neurological disorders, such as Parkinson's disease, are conditions that affect your nerves. Low blood pressure can occur if part of your nervous system called the autonomic nervous system is affected.

Your autonomic nervous system controls bodily functions you don't actively think about, such as sweating and digestion. It also controls the widening and narrowing of your blood vessels.

If there's a problem with your autonomic nervous system, your blood vessels could remain too wide, which can cause low blood pressure.

Hormone problem

Having a condition that affects the production of certain hormones in your body can also cause low blood pressure. Examples are diabetes and Addison's disease.

In Addison's disease, the immune system attacks and damages the adrenal glands, two small glands above your kidneys that produce hormones to control your blood pressure and maintain the balance of salt and water in your body.

Low blood pressure can also occur if your adrenal glands become damaged - for example, because of an infection or tumour.  

Miscommunication between the heart and brain

Low blood pressure that occurs after standing for long periods of time (neurally mediated hypotension) happens when your body tells the brain your blood pressure is too high when it's actually too low. This causes your brain to slow down the heartbeat, further reducing your blood pressure.

Serious injury and shock

Low blood pressure can be caused by serious injuries or burns, particularly if you lose a lot of blood. Low blood pressure can also occur if you go into shock after a serious injury.

Septic shock and toxic shock syndrome

Septic shock and toxic shock syndrome are caused by bacterial infections. Bacteria attack the walls of the small blood vessels, causing them to leak fluid from the blood into the surrounding tissues. This causes a significant drop in blood pressure.

Anaphylactic shock

Anaphylactic shock, or anaphylaxis, is caused by an allergic reaction. During an allergic reaction, your body produces a large amount of a chemical called histamine, which causes your blood vessels to widen, leading to a sudden severe drop in blood pressure.

Cardiogenic shock

Cardiogenic shock occurs when your heart cannot supply enough blood to your body, leading to a drop in blood pressure. This can happen during a heart attack.

Diagnosing low blood pressure

Diagnosing low blood pressure

Low blood pressure (hypotension) can be easily diagnosed by measuring your blood pressure. You may need further tests, such as blood tests or an electrocardiogram (ECG), to determine the underlying cause.

Blood pressure testing is available in a variety of settings:

  • at your GP surgery - by a GP, practice nurse, healthcare assistant or self-service machine
  • at a pharmacy
  • as part of your NHS Health Check
  • in some workplaces
  • at a health event
  • at home - you can check blood pressure yourself with a home testing kit

Healthy adults aged over 40 should have their blood pressure checked at least once every five years.

How blood pressure is measured

Blood pressure is often measured using a sphygmomanometer, a device that consists of a stethoscope, arm cuff, dial, pump and valve.

The cuff is placed around your arm and pumped up to restrict the blood flow. The pressure is then slowly released as your pulse is checked using the stethoscope.

A measurement is taken on the mercury scale, giving an accurate reading of your blood pressure.

Many GP surgeries now use digital sphygmomanometers, which measure your pulse using electrical sensors.

Before having your blood pressure taken, you should rest for at least five minutes and empty your bladder.

To get an accurate blood pressure reading, you should be sitting down and not talking when the reading is taken.

Postural or orthostatic hypotension

If your symptoms of low blood pressure mostly occur when you suddenly move into a more vertical position, your blood pressure may be measured before and after you move. For example, your blood pressure may be measured while you are sitting down and again while you are standing up.

Depending on what your seated blood pressure is, if your systolic reading falls by between 15 to 30mmHg when you stand up, you may have orthostatic hypotension (also known as postural hypotension).

Understanding your blood pressure reading

Blood pressure is measured in millimetres of mercury (mmHg) and is recorded as two figures:

  • systolic pressure (the top number) - the pressure of the blood when your heart pushes blood out
  • diastolic pressure (the bottom number) - the pressure of the blood when your heart rests in between beats, which reflects how strongly your arteries are resisting blood flow

If your GP says your blood pressure is "140 over 90" or 140/90mmHg, it means you have a systolic pressure of 140mmHg and a diastolic pressure of 90mmHg.

As a general guide, low blood pressure is a reading below 90/60. If you have low blood pressure according to this guide, you don't need to worry. Naturally low blood pressure rarely causes symptoms or needs treatment. Having low blood pressure is considered healthy because it protects you from the risks and diseases of high blood pressure.

Treating low blood pressure

Treating low blood pressure

Low blood pressure (hypotension) usually only needs to be treated if it's causing symptoms. This involves general lifestyle advice and treating any underlying cause of the condition.

If you have naturally low blood pressure and it's not causing any problems, treatment is rarely necessary.

General advice

The advice outlined below can often help limit symptoms of some of the most common types of hypotension:

  • stand up gradually - particularly first thing in the morning. It may also be useful to try other physical movements first to increase your heart rate and the flow of blood around your body. For example, stretching in bed before you get up, or crossing and uncrossing your legs if you're seated and about to stand. 
  • avoid standing for long periods of time - this can help prevent neurally mediated hypotension (low blood pressure caused by miscommunication between the heart and brain).
  • wear support stockings - sometimes called compression stockings, these are tight-fitting elastic socks or tights. They provide extra pressure to your feet, legs and tummy, which can help improve circulation and increase blood pressure. However, you should speak to your GP before using support stockings as they're not suitable for everyone.
  • avoid caffeine at night, and limit your alcohol intake - this can help you to avoid becoming dehydrated, which can also cause low blood pressure.
  • eat small, frequent meals rather than large ones - this can help prevent postprandial hypotension (low blood pressure after eating). Lying down after eating or sitting still for a while may also help.

Increasing your fluid and salt intake

Dehydration can cause low blood pressure. This can be easily treated by increasing your fluid and salt intake. Ensuring you drink enough fluid will help by increasing the volume of your blood, which increases your blood pressure.

If you have low blood pressure, you may benefit from having more salt in your diet. Your GP can advise how much additional salt you need and whether you can add salt to your usual food or take salt tablets. Don't add extra salt to your diet without seeing your GP first.

Changing your medication

If your GP suspects your medication is causing low blood pressure, they may alter your dose or advise using an alternative medication.

Your blood pressure should be monitored while you're taking medication and any changes should be noted. Tell your GP if you're experiencing side effects from taking medication.

Treating underlying conditions

If your GP suspects your low blood pressure is caused by an underlying health condition, you may be referred to hospital for further tests and treatment.

For example, if your low blood pressure is related to hormone problems, you may be referred to a specialist called an endocrinologist who may prescribe hormone replacement medication.

See causes of low blood pressure for more information.

Medication for low blood pressure

Very few people are prescribed medication for low blood pressure. The symptoms of hypotension can usually be treated by making the above changes to your lifestyle and, in particular, by increasing your fluid and salt intake.

If medication is necessary, it will usually be medicine to expand the volume of your blood or narrow your arteries. Your blood pressure will increase as there will be more blood flowing through a smaller space.