Hypotension: what is low blood pressure?

You may have heard that high blood pressure is bad for your health, but did you know that low blood pressure, known as hypotension, can cause problems too?

What is low blood pressure?

Blood pressure is the force at which your heart pumps blood around your body. The measurement is given as two figures, for example “100 over 70” or 100/70mmHg. The mmHg stands for millimetres of mercury and the two numbers are the systolic pressure, when your heart pushes blood out, and the diastolic pressure, when your heart is resting between beats.

Normal blood pressure is usually classed as anything between 90/60mmHg and 120/80mmHg. If your reading is below 90/60mmHg, this is classed as low blood pressure.

What causes low blood pressure?

Anyone can experience low blood pressure and many of us do at some point in our life. Age is one of the biggest risk factors, with decreases in blood pressure on standing or after eating more likely to affect people over the age of 65.

Hypotension can also be caused by some types of medication. Water pills (diuretics), beta blockers, some antidepressants, medications for Parkinson’s disease and drugs to treat erectile dysfunction can all cause low blood pressure.

Other causes of hypotension include:

• Blood loss — if you lose a lot of blood your blood pressure will drop
• Dehydration — fever, vomiting, diarrhoea and strenuous exercise, can mean your body uses more water than it takes in, causing hypotension
• Endocrine problems eg diabetes, low blood sugar, adrenal insufficiency and thyroid problems
• Heart problems eg heart failure, heart attack, low heart rate (bradycardia) and heart valve problems 
• Infection in the bloodstream (septicemia) — if an infection spreads to the bloodstream it can cause septic shock, which is life threatening
• Severe allergic reaction (anaphylaxis) — as well as a swollen throat and breathing problems, anaphylaxis can also cause a serious drop in blood pressure

It’s also common to have a lower blood pressure during pregnancy but sudden or big drops can be a sign of an underlying condition.

Hypotension symptoms

Low blood pressure does not always cause symptoms. Some people have naturally low blood pressure and it doesn’t affect them. If you do experience symptoms these can include:

• Blurred vision
• Confusion
• Dizziness
• Fainting or lightheadedness
• Feeling weak
• Nausea

These symptoms can be caused by other conditions, so get your blood pressure checked to rule out or confirm low blood pressure as the cause. You can do this at your GP surgery, pharmacy or using your own blood pressure machine at home.

Types of hypotension

Some people feel symptoms of hypotension when they change position or stand up, which is known as orthostatic or postural hypotension. If this is the case you can manage your symptoms by being careful not to stand or change position too quickly.

Postprandial hypotension is when blood pressure drops after eating. It usually happens in older adults, particularly those with Parkinson's disease.

Sometimes, blood pressure can drop after standing up for a long time, which is known as neurally mediated hypotension. This is more common in children and young adults.

Extreme or severe hypotension can lead to shock. It happens when your organs don’t get enough blood and oxygen to work properly and can be life threatening.

Symptoms include:

• Cold, clammy skin
• Fast, shallow breathing
• Weak, rapid pulse

If you have these symptoms, it is important to seek medical help urgently. 

When to see a doctor

If you’re experiencing any symptoms of hypotension, make an appointment with your GP. They can test your blood pressure and look at any medication you’re taking to find the underlying cause. If needed, they may adjust the dosage of medication you’re taking or try an alternative medication.

Hypotension diagnosis

Hypotension is usually diagnosed with a blood pressure test. Your doctor may want to take your blood pressure while sitting and standing, or they may want to do a tilt table test, where you lie on a table that starts horizontal then tilts you so you’re almost standing while monitoring your blood pressure. 

Your GP may want to monitor your blood pressure for a period of time before making a diagnosis. 

Treatment for hypotension

The way your low blood pressure is treated will depend on the cause. Sometimes it is a simple change in medication. If you’re diagnosed with an endocrine condition, you may be referred to a specialist or given medication to treat the condition. Some people are advised by their doctor to wear compression stockings to improve their circulation. If you’re found to have a neurological condition you may be given medication that helps stimulate your nerves.

Avoiding hypotension

There are some things you can do at home to avoid experiencing low blood pressure symptoms. If you tend to get postural hypotension, be careful to stand up slowly and move your legs around before standing to get your blood flowing better.

Make sure you drink plenty of water each day so you don’t get dehydrated. If you get low blood pressure after eating, try eating little and often rather than having large meals. Finally, make sure you get enough nutrients in your diet to ensure your iron and vitamin B12 levels are good — deficiency in either vitamin B12 or iron can prevent your body from producing enough red blood cells, leading to hypotension.