Understanding high blood pressure (hypertension)

Mr Erick Mbaabu, a nurse at Karen hospital in Nyeri tests blood pressure on a patient during a past corporate health check. Photo/ JOSEPH KANYI

What you need to know:

• According to the World Health Organization, high blood pressure affects more than one in three adults worldwide.
• Most people with high blood pressure don’t have any symptoms.
• Lifestyle factors such as smoking, obesity and drinking alcohol excessively can contribute to causing high blood pressure.
• Having high blood pressure increases your risk of cardiovascular disease, such as stroke and heart attack.

Blood pressure is a measure of the force that your blood applies to the walls of your arteries as it flows through them. It's normal for your blood pressure to temporarily increase when you exert yourself, or when you feel anxious or stressed. But if your blood pressure is consistently higher than the healthy level when at rest, this is called high blood pressure (hypertension).

Blood pressure is an essential part of the way your body works. Your blood carries oxygen and nutrients around your body and is pumped by your heart. Your blood is under pressure as a result of the pumping action of your heart and the size and flexibility of your arteries, which carry your blood.

If the walls of your arteries lose their elasticity, become narrow or contract too much, you can get high blood pressure. Your blood pressure can also rise if your heart pumps too much blood or you have too much blood in your circulation.

According to the World Health Organization, high blood pressure affects more than one in three adults worldwide.

Symptoms of high blood pressure

Most people with high blood pressure don't have any symptoms, so you may only find out you have high blood pressure by having it checked.

If you have very high blood pressure, or your blood pressure rises quickly, you may have headaches, problems with your vision, fits or black-outs – but this is very uncommon.

Complications of high blood pressure

If you have high blood pressure, you have an increased risk of:

• cardiovascular disease, such as angina (chest pain caused by reduced blood flow), stroke, heart attack, heart failure or atrial fibrillation (irregular heart beat)

• kidney damage

• damage to the back of your eye, which can affect your vision

Causes of high blood pressure

Depending on the cause, high blood pressure can be diagnosed as primary or secondary hypertension.

Primary hypertension

The majority of people with high blood pressure have primary hypertension. This means there is no single cause, but various lifestyle factors can contribute, including:

• smoking

• obesity (being very overweight)

• drinking alcohol excessively – especially if you binge drink

• lack of exercise

• your diet, particularly salt intake

If someone else in your family has high blood pressure, you also have a higher risk of developing it.

Secondary hypertension

Some people with high blood pressure have secondary hypertension. This means there is a known underlying cause – examples include:

• kidney disease

• endocrine disease (hormone disorders)

• a narrowing of part of your aorta (the largest artery leading from your heart) or the arteries leading to your kidneys

Secondary hypertension can also be caused by:

• steroid medicines

• the contraceptive pill

• pregnancy, which can lead to pre-eclampsia – this can be serious and harm your baby

Diagnosis of high blood pressure

Your doctor may diagnose you with high blood pressure when he or she measures it as part of a medical examination. This is a good reason to have regular check-ups with your doctor, especially if you're over 40.

Your doctor or nurse will measure your blood pressure with a sphygmomanometer. He or she will place a cuff around your upper arm, inflate it to a certain level and then deflate it slowly.

Your blood pressure is measured in mmHg, or millimetres of mercury. The blood pressure monitor will provide a reading as two numbers, one number on top of the other, such as 120/80mmHg (one hundred and twenty over eighty millimetres of mercury).

• The first figure is called systolic blood pressure. This is a measure of the pressure when your heart muscle is contracted and pumping blood out of your heart. This is the highest pressure in your blood vessels.

• The second figure is called diastolic blood pressure. This is the pressure between heart beats when your heart is resting and filling with blood. This is the lowest pressure in your blood vessels.

Generally speaking, the lower your blood pressure, the better it is for your health. Doctors usually recommend your blood pressure is below 140/90mmHg. If you have diabetes, kidney disease or cardiovascular disease, your doctor may recommend your blood pressure should be lower than this.

Your doctor may ask you to come back for repeat measurements over a number of weeks and arrange a 24-hour blood pressure recording before suggesting you have treatment. This is so he or she can check that the high reading is an ongoing problem and not a one-off.

You may also need some tests to see if high blood pressure is affecting the rest of your body. These may include:

• a urine test – protein in your urine may be the first sign of damage to your kidneys

• a blood test to check your cholesterol and blood sugar levels, as well as the condition of your kidneys

• an electrocardiogram (ECG) – a test that measures the electrical activity of your heart to check for signs of heart enlargement or other damage

Please note that availability and use of specific tests may vary from country to country.


If you have a high blood pressure reading, you may be given 24-hour ambulatory blood pressure monitoring (ABPM). This is because some people have a high reading when they see a doctor, but normal blood pressure at other times (so-called ‘white coat hypertension’).

A monitoring device is strapped around your waist and attached to a cuff, which is wrapped around your upper arm. The cuff inflates and deflates automatically and takes recordings of your blood pressure throughout the 24 hours.

You can carry on with your usual activities whilst wearing the monitor, except for having a bath or shower. Your doctor will use the measurements to find out your average blood pressure.

In some cases, another form of home blood pressure monitoring (HBPM) may be used to confirm your diagnosis. Your doctor may provide a blood pressure monitor for you to record your blood pressure twice a day at home, in the morning and evening, for four to seven days.

You might also consider getting a blood pressure monitor to use yourself at home on a regular basis. This can help you identify situations or activities in your daily life that cause your blood pressure to rise.

If you’re having treatment for blood pressure, it may also help you to see how your treatment is working. Even if you use a blood pressure monitor at home, you should continue to have your blood pressure tested regularly by your doctor.

Treatment of high blood pressure

If you need treatment, it’s likely to be long-term as high blood pressure can’t usually be cured. You may need to go to hospital for treatment if you have very high blood pressure, but it's much more likely that your doctor and/or a nurse will look after you.


Your doctor will talk to you about lifestyle changes that might help, such as:

• stopping smoking

• changing your diet to be low-fat, low-salt and including fruit and vegetables

• cutting down on alcohol

• cutting down on coffee and high-caffeine drinks, such as cola

• taking regular, aerobic exercise

• losing any excess weight

It may also help, where possible, to reduce stress in your life to prevent short-term rises in blood pressure – you could try relaxation techniques or meditation.


If your blood pressure stays high, your doctor may prescribe you one or more of the following antihypertensive medicines.

• ACE inhibitors (eg ramipril) or angiotensin-II receptor antagonists (eg candesartan) – these relax and widen the walls of your blood vessels by reducing the production of hormones that cause your blood vessels to constrict (narrow).

• Calcium-channel blockers (eg amlodipine) – these help to widen your blood vessels by relaxing the muscles in your blood vessel walls.

• Diuretics (eg indapamide) – these increase the amount of water and salt removed from your blood by your kidneys, lowering the volume of your blood, which reduces blood pressure.

If your symptoms don’t improve, then your doctor may prescribe one of the following.

• Beta-blockers (eg atenolol) – these reduce the work your heart has to do by reducing your pulse rate and the force of contraction of your heart at rest and when you exercise.

• Alpha-blockers (eg doxazosin) – these help to widen your blood vessels by relaxing the muscles in your blood vessel walls.

The medicines your doctor prescribes will depend on a number of factors, including your age and ethnicity. It may take time to find the best treatment for you; one that balances the benefits against any side-effects.

It's important to take your medicines every day, even if you don't have any symptoms.

Availability and use of different treatments may vary from country to country. Ask your doctor for advice on your treatment options.

Special considerations


If you're pregnant, your blood pressure may be monitored regularly, regardless of whether you have high blood pressure or not. Long-term high blood pressure may be picked up at an antenatal appointment.

It's also possible that you may develop high blood pressure during your pregnancy (gestational hypertension). High blood pressure that develops after 20 weeks of pregnancy can mean you have pre-eclampsia.

If you have high blood pressure and think you may be, or are trying to become pregnant, it's important to speak to your doctor. Certain medicines for treating high blood pressure aren't suitable for pregnant women.

Ethnic groups

If you're of African-Caribbean origin, you're at a higher risk of high blood pressure and should visit your doctor to discuss how often you need to have your blood pressure checked.

You should also be monitored regularly if you're of South-Asian origin because you have a higher risk of developing heart disease and diabetes.