Patient information from BMJ


High blood pressure: what is it?

Last published: Dec 16, 2020

If you have high blood pressure you probably won't feel ill. But having high blood pressure increases your chance of serious health problems, including heart attacks and strokes.

There are good treatments, and things you can do yourself, to reduce your blood pressure.

What is high blood pressure?

When doctors take your blood pressure, they measure how hard your blood pushes against your blood vessels as it moves around your body. You need some pressure to keep the blood moving. But if the pressure is too high, over time it can damage your blood vessels.

This can cause problems such as heart attacks, strokes, eye problems, and kidney damage.

Your blood pressure rises and falls slightly throughout the day and night. But when it stays above a certain level, it's called high blood pressure. High blood pressure is also called hypertension.

Doctors measure blood pressure with two numbers:

  • The first number measures your blood pressure when your heart beats (this is called systolic pressure).
  • The second number measures your blood pressure when your heart relaxes and fills with blood (this is called diastolic pressure).

Your doctor will probably describe your blood pressure using these two numbers: for example, '140 over 90'.

Usually, doctors will say you have high blood pressure if either your first number is higher than 140 or your second number is higher than 90.

However, if you have kidney disease, your doctor will say you have high blood pressure if either your first number is higher than 130 or your second number is higher than 80.

You are more likely to have high blood pressure if you:

  • are older
  • have a close relative with high blood pressure
  • have certain medical conditions (such as diabetes or sleep apnoea)
  • are black
  • are overweight
  • drink moderate to high amounts of alcohol, or
  • don’t exercise.

What are the symptoms?

Most people with high blood pressure don't get any symptoms. You can't feel when your blood pressure goes up, although occasionally people with very high blood pressure say they had bad headaches before they were treated.

The only way to find out if your blood pressure is high is to have it measured.

People usually find out they have high blood pressure after a routine blood pressure check.

Your doctor will measure your blood pressure using an inflatable cuff that goes around your upper arm. You’ll need to have your blood pressure measured on two or more occasions to make sure it’s not just a one-off high reading. You should also have it measured in both arms.

If your reading is high, your doctor may recommend that you measure your own blood pressure at home.

Another option is to wear a device that measures your blood pressure several times over the course of one day (this is called ambulatory blood pressure monitoring).

Blood pressure goes up and down during the day, so home and ambulatory monitoring can help confirm whether your blood pressure is high.

Also, some people feel nervous when having their blood pressure taken by a doctor or nurse, and this can lead to a temporarily raised blood pressure reading.

You might hear this called 'white coat hypertension', named after the white coats that healthcare professionals sometimes wear.

What will happen to me?

The main health problems related to high blood pressure are heart attacks, strokes, heart failure, eye problems, and kidney failure.

But not everybody with high blood pressure will get these problems. Your chance of these problems depends on several things, including:

  • how high your blood pressure is
  • how long you've had high blood pressure
  • whether you have other health problems (such as high cholesterol or diabetes)
  • how closely you follow your doctor's treatment recommendations. This includes taking your medicines as directed and making changes to your lifestyle.

The good news is that the harmful effects of high blood pressure don't happen overnight. They usually take many years to develop. And if you control your high blood pressure you can reduce the chance that they will ever happen.

Where to get more help

Many resources are available to provide advice and support for people with high blood pressure. You can ask your doctor or nurse for recommendations.

In the UK, one resource is the Blood Pressure Association (bloodpressureuk.org).

For more information on treatments for high blood pressure see our leaflet High blood pressure: what treatments work?

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