High blood pressure is a risk factor that can increase your chance of developing heart disease, a stroke, and other serious conditions. As a rule, the higher the blood pressure, the greater the risk. Treatment includes a change in lifestyle risk factors where these can be improved - losing weight if you are overweight, regular physical activity, a healthy diet, cutting back if you drink a lot of alcohol, stopping smoking, and a low salt and caffeine intake. If needed, medication can lower blood pressure.

What is blood pressure?

Blood pressure is the pressure of blood in your arteries. Blood pressure is measured in millimetres of mercury (mm Hg). Your blood pressure is recorded as two figures. For example, 150/95 mm Hg. This is said as 150 over 95.

  • The top (first) number is the systolic pressure. This is the pressure in the arteries when the heart contracts.
  • The bottom (second) number is the diastolic pressure. This is the pressure in the arteries when the heart rests between each heartbeat.
Some phrases and definitions
Clinic/GP surgery blood pressure readings: these are readings taken by a doctor or nurse in a clinic or GP surgery using a standard blood pressure machine.

Home blood pressure readings: these are readings taken by a person whilst seated and at rest at home using a standard blood pressure machine.

Ambulatory blood pressure readings: these are readings taken at regular intervals whilst you go about your normal activities. A small machine that is attached to your arm takes and records the readings.

As a rule, an average of the ambulatory blood pressure readings give the most true account of your usual blood pressure. Home blood pressure readings are a good substitute if an ambulatory machine is not available. Ambulatory and home readings are often a bit lower than clinic or GP surgery readings. Sometimes they are a lot lower. This is because people are often much more relaxed and less stressed at home than in a formal clinic or surgery situation.

What is high blood pressure / hypertension?

High blood pressure is a blood pressure that is 140/90 mm Hg or above each time it is taken at the GP surgery (or home or ambulatory readings always more than 135/85 mm Hg). That is, it is sustained at this level. High blood pressure can be:

  • Just a high systolic pressure - for example, 170/70 mm Hg.
  • Just a high diastolic pressure - for example, 120/104 mm Hg.
  • Or both - for example, 170/110 mm Hg.

However, it is not quite as simple as this. Depending on various factors, the level at which blood pressure is considered high enough to be treated with medication can vary from person to person.
Blood pressure of 140/90 mm Hg or above (or home/ambulatory readings 135/85 mm Hg or above)
If your blood pressure is always in this range you will normally be offered treatment to bring the pressure down, particularly if you have:
  • A high risk of developing cardiovascular diseases (see below); or
  • An existing cardiovascular disease (see below); or
  • Diabetes; or
  • Damage to the heart or kidney (organ damage) due to high blood pressure.
Blood pressure between 130/80 mm Hg and 140/90 mm Hg
For most people this level is fine. However, current UK guidelines suggest that this level is too high for certain groups of people. Treatment to lower your blood pressure if it is 130/80 mm Hg or higher may be considered if you:
  • Have developed a complication of diabetes, especially kidney problems.
  • Have had a serious cardiovascular event such as a heart attack, transient ischaemic attack (TIA) or stroke.
  • Have certain chronic (ongoing) kidney diseases.

How is high blood pressure diagnosed?

A one-off blood pressure reading that is high does not mean that you have 'high blood pressure'. Your blood pressure varies throughout the day. It may be high for a short time if you are anxious, stressed, or have just been exercising.

You have high blood pressure (hypertension) if you have several blood pressure readings that are high, and which are taken on different occasions, and when you are relaxed.

Observation period
If one reading is found to be high, it is usual for your doctor or nurse to advise a time of observation. This means several blood pressure checks at intervals over time. The length of the observation period varies depending on the initial reading, and if you have other health risk factors.

For example, say a first reading was mildly high at 150/94 mm Hg. If you are otherwise well, then a period of several weeks of observation may be advised. This may involve several blood pressure measurements over the next few weeks. You may be given a machine to monitor blood pressure while you are going about doing your everyday activities (ambulatory monitoring) or given (or asked to buy) a machine to measure your blood pressure at home (home monitoring). One reason this may be advised is because some people become anxious in medical clinics, which can cause the blood pressure to rise. (This is often called white coat hypertension.) Home or ambulatory monitoring of blood pressure may show that the blood pressure is normal when you are relaxed.

The observation period is also a good time to change any lifestyle factors that can reduce blood pressure (see below). If the blood pressure readings remain high after an observation period then medication may be advised, depending on your risk factors (see below).

However, if you have diabetes, or have recently had a heart attack or stroke, you may be advised to have blood pressure checks fairly often over the next week or so. Also, treatment with medication is usually considered at an earlier stage if the readings remain high.

What are the high blood pressure causes? 

The cause is not known in most cases

This is called essential hypertension. The pressure in the arteries depends on how hard the heart pumps, and how much resistance there is in the arteries. It is thought that slight narrowing of the arteries increases the resistance to blood flow, which increases the blood pressure. The cause of the slight narrowing of the arteries is not clear. Various factors probably contribute.

In some cases, high blood pressure is caused by other conditions

It is then called secondary hypertension. For example, certain kidney or hormone problems can cause high blood pressure.

How common is high blood pressure?

In the UK, about half of people aged over 65, and about 1 in 4 middle-aged adults, have high blood pressure. It is less common in younger adults. Most cases are mildly high (up to 160/100 mm Hg). However, at least 1 in 20 adults have blood pressure of 160/100 mm Hg or above. High blood pressure is more common in people:
  • With diabetes. About 3 in 10 people with type 1 diabetes and more than half of people with type 2 diabetes eventually develop high blood pressure.
  • From African-Caribbean origin.

  • From the Indian subcontinent.

  • With a family history of high blood pressure.

  • With certain lifestyle factors. That is, those who: are overweight, eat a lot of salt, don't eat sufficient fruit and vegetables, don't take enough exercise, drink a lot of coffee (or other caffeine-rich drinks), or drink a lot of alcohol.

Who should have a blood pressure check?

High blood pressure usually causes no symptoms. You will not know if you have high blood pressure unless you have your blood pressure checked. Therefore, everyone should have regular blood pressure checks at least every five years. The check should be more often (at least once a year) in: older people, people who have had a previous high reading, people with diabetes, and people who have had a previous reading between 130/85 mm Hg and 139/89 mm Hg (that is, not much below the cut-off point for high blood pressure).

If there are no high blood pressure (hypertension) symptoms, why is it a problem?

High blood pressure is a risk factor for developing a cardiovascular disease (such as a heart attack or stroke), and kidney damage, sometime in the future. If you have high blood pressure, over the years it may do some damage to your arteries and put a strain on your heart. In general, the higher your blood pressure, the greater the health risk. But, high blood pressure is just one of several possible risk factors for developing a cardiovascular disease.

What are cardiovascular diseases?

Cardiovascular diseases are diseases of the heart (cardiac muscle) or blood vessels (vasculature). However, in practice, when doctors use the term cardiovascular disease they usually mean diseases of the heart or blood vessels that are caused by atheroma. Patches of atheroma are like small fatty lumps that develop within the inside lining of arteries (blood vessels). Atheroma is also known as atherosclerosis and hardening of the arteries.

Cardiovascular diseases that can be caused by atheroma include: angina, heart attack, stroke, transient ischaemic attack (TIA), and peripheral vascular disease. In the UK, cardiovascular diseases are a major cause of poor health and the biggest cause of death.

Risk factors for cardiovascular diseases

Everybody has some risk of developing atheroma which may cause one or more cardiovascular diseases. However, certain risk factors increase the risk. These include:

Lifestyle risk factors that can be prevented or changed:
  • Smoking.
  • Lack of physical activity (a sedentary lifestyle).
  • Obesity.

  • An unhealthy diet.

  • Excess alcohol.
Treatable or partly treatable risk factors:
  • Hypertension (high blood pressure).

  • High cholesterol blood level.

  • High triglyceride (fat) blood level.

  • Diabetes.

  • Kidney diseases that affect kidney function.
Fixed risk factors - ones that you cannot alter:
  • A strong family history. This means if you have a father or brother who developed heart disease or a stroke before they were aged 55, or in a mother or sister before they were aged 65.

  • Being male.
  • An early menopause in women.
  • Age. The older you become, the more likely you are to develop atheroma.
  • Ethnic group. For example, people who live in the UK with ancestry from India, Pakistan, Bangladesh, or Sri Lanka have an increased risk.

However, if you have a fixed risk factor, you may want to make extra effort to tackle any lifestyle risk factors that can be changed.

Note: some risk factors are more risky than others. For example, smoking and high blood pressure probably cause a greater risk to health than obesity. Also, risk factors interact. So, if you have two or more risk factors, your health risk is much more increased than if you just have one. For example, a middle-aged male smoker who takes no exercise and has high blood pressure has a high risk of developing a cardiovascular disease such as a heart attack before the age of 60.

Therefore, the benefit of lowering a high blood pressure is to reduce the risk of developing a cardiovascular disease in the future.

For example, it is estimated that reducing a high diastolic blood pressure by 6 mm Hg reduces your relative risk of having a stroke in the future by about 35-40%, and reduces your relative risk of developing heart disease by about 20-25%. Larger reductions in blood pressure provide greater benefits.

Assessing (calculating) your cardiovascular health risk

A risk factor calculator is often used by doctors and nurses to predict the health risk for an individual. A score is calculated which takes into account all your risk factors, such as age, sex, smoking status, blood pressure, blood cholesterol level, etc. If you want to know your score, see your practice nurse or GP.

Current UK guidelines advise that if your score gives you a 2 in 10 risk or more of developing a cardiovascular disease within the next 10 years, then treatment is advised.

Treatments may include:
  • A medicine to lower blood pressure if it is 140/90 mm Hg or higher.
  • A medicine to lower your cholesterol level.

  • A daily low dose of aspirin if you also have angina. This reduces the risk of blood clots forming in the blood vessels over patches of atheroma (which cause strokes and heart attacks).

  • Where relevant, to encourage you to tackle lifestyle risk factors such as smoking, lack of physical activity, diet, and weight.

Do I need any further tests?

If you are diagnosed as having high blood pressure then you are likely to be examined by your doctor and have some routine tests which include:
  • A urine test to check if you have protein or blood in your urine.
  • A blood test to check that your kidneys are working fine, and to check your cholesterol level and sugar (glucose) level.
  • A heart tracing, called an electrocardiogram (ECG).

The purpose of the examination and tests is to:
  • Rule out (or diagnose) a secondary cause of high blood pressure, such as kidney disease. 
  • To check to see if the high blood pressure has affected the heart.
  • To check for other risk factors such as a high cholesterol level or diabetes.