Low blood pressure

What is blood pressure?

Blood pressure is a measure of the force that your heart uses to pump blood around your body. It’s measured in millimetres of mercury (mmHg) and has 2 figures:

1. Systolic pressure measures the pressure exerted when your heart pushes out blood

2. Diastolic pressure reflects the pressure of your heart at rest between beats.

If your blood pressure reads 120/80mmHg, then 120mmHg is the systolic and 80mmHg is the diastolic pressure.

What is low blood pressure?

A normal blood pressure for an adult over 18 is 120/80mmHg.

Low blood pressure means having a systolic blood pressure of <90mmHg or a diastolic pressure <60mmHg. It is the opposite of hypertension which is high blood pressure (>140mmHg/90mmHg).

Some people naturally have a low blood pressure and this causes no problem but, in others, there can be an underlying problem.

There are three major types of low blood pressure:

• Orthostatic (postural) hypotension

• Postprandial hypotension

• Neurally mediated hypotension

What is considered dangerously low blood pressure?

If blood pressure reaches dangerously low levels it can deprive the organs of nutrients and oxygen. This is because pressure is required to pump blood - and this provides oxygen for organs to function. This is called shock and can be life-threatening.

How to measure low blood pressure

You can check if you have low blood pressure either by asking a pharmacist or a GP practice nurse to measure it for you. You can also do it yourself if you have a home blood pressure monitor.

What is low blood pressure affected by?

It is natural for your blood pressure to fluctuate throughout the day. It can be affected by:

• Food and drink

• Medications

• Stress

• Body position

Low blood pressure symptoms

Symptoms of low blood pressure can include:

• Lightheadedness and dizziness

• Feeling weak

• Blurred or tunnel vision

• Confusion

• Fainting

• Nausea

Additionally, features of the underlying cause of low blood pressure can also be present, for example:

• Chest pain

• Shortness of breath

• Fever

• Infection

• Anaphylaxis

Serious but less common symptoms of low blood pressure may include:

• Rapid but weak pulse

• Rapid shallow breathing

• Paleness

• Cold, clammy skin

If you have any of these serious symptoms, seek urgent medical help.

What causes low blood pressure?

• Not drinking enough water

• Peeing too often

• Using diuretics

• Excessive sweating

• Loss of fluids from vomiting or diarrhoea

• Side effects from drugs used for hypertension, angina and erectile dysfunction

Underlying medical conditions such as heart failure, heart attack, bradycardia, an underactive thyroid and Addison’s diabetes.

What is orthostatic (postural) hypotension?

Postural hypotension is a drop in blood pressure after standing up from sitting or lying down. It is more common in older adults. 

A fall in systolic blood pressure of at least 20mmHg or a fall in diastolic blood pressure of at least 10mmHg within 3 minutes of standing can indicate postural hypotension.

What causes low blood pressure in pregnancy?

There are many changes to the body in pregnancy and this can affect blood pressure. Hormones can cause the walls of blood vessels to relax, lowering the blood pressure. Blood pressure is at its lowest in mid-pregnancy and starts to rise gradually again in your last trimester.

Symptoms of low blood pressure in pregnancy include dizziness, fatigue, postural hypotension, vision impairment and shortness of breath.

Does your blood pressure drop when you sleep?

Blood pressure usually drops during sleep. This is known as nocturnal dipping and can be as much as 20% lower than your daytime blood pressure.

Low blood pressure treatment

Lifestyle changes

These simple changes to your lifestyle can help manage your blood pressure.:

• Eat more salt – the sodium in salt can raise your blood pressure, but it’s important that you check with a doctor before increasing your salt intake as this can be dangerous if you have other medical conditions

• Increase your water intake – the increase in fluids can increase the blood volume and prevent dehydration

• Drink less alcohol – alcohol can dehydrate you and further lower your blood pressure

• Exercise regularly – 30 minutes a day through low to moderate intensity can make a difference, for example walking, yoga and gardening

• Eat low-carb meals –  foods high in carbohydrates can cause a sharp drop in your blood pressure

• Try wearing compression stockings – these improve blood flow from the legs to the heart and increase blood flow

• Stand up slowly – try to squeeze your leg muscles and bend at the knee when you stand up

• Use multiple pillows to elevate your head while you sleep

• Keep a BMI of 19 to 25 – Low blood pressure tends to be more common if you are underweight

Medication 

Sometimes your doctor may recommend starting medication for low blood pressure. There are a few different medications that can be used but examples include fludrocortisone or midodrine.

When to see a GP for low blood pressure

See a GP if you experience the symptoms of low blood pressure such as dizziness and fainting.