Diabetes and high blood pressure

Keeping your blood pressure well controlled is important for everyone, but is especially important for people with diabetes. High blood pressure (hypertension) increases the risk of developing heart disease and stroke, and in people with diabetes it also increases the risk of several complications of diabetes, such as feet, eye, and kidney problems. Treatment includes a change in lifestyle risk factors where these can be improved. Many people with diabetes also need to take medication to lower their blood pressure.

How common is high blood pressure in people with diabetes?

In the UK, about 1 in 4 of people have high blood pressure (hypertension). It is less common in younger adults. High blood pressure is more common in people with diabetes. Around 3 in 10 people with type 1 diabetes and around 8 in 10 people with type 2 diabetes develop high blood pressure at some stage.

People with diabetes are more at risk of developing high blood pressure if they:

• Have African-Caribbean ancestry.

• Have South Asian ancestry.

• Have a family history of high blood pressure.

• Have certain lifestyle factors - for example, those who:

  • Are overweight.

  • Eat a lot of salt.

  • Do not eat much fruit and vegetables.

  • Do not take much exercise.

  • Drink a lot of alcohol.

What is high blood pressure?

This is not as simple to answer as it may seem. In general, the higher the blood pressure, the greater the risk to health. Depending on various factors, the level at which blood pressure is said to be high (hypertension) can vary from person to person.

There are various different cut-off points for 'high' blood pressure, also known as blood pressure targets. These are generally chosen at the point at which the benefits of reducing blood pressure outweigh the risks - making blood pressure too low with medications can cause problems.

The usual cut-off points, over which blood pressure can be considered 'high', are:

• 140/90 mm Hg or higher for people under 80, including people with diabetes.

• 130/80 mm Hg or higher for people under 80 with diabetes and certain types of kidney disease.

Blood pressure targets are a bit higher in people over 80 (150/90 mm Hg for most people, including people with diabetes, though targets are lower for people with kidney disease). This is because older people are more likely to have problems if their blood pressure drops too low with treatment, such as falls. There is also a bit of evidence that a slightly raised blood pressure may be helpful in older, frail people.

Note: Blood pressure values normally go up and down throughout the course of a day. For example, blood pressure increases if you are in pain, or stressed or anxious, and this is a normal response. If your blood pressure goes back down and is normal most of the time, it's not a problem.

So, a one-off raised blood pressure reading doesn't necessarily mean that you have high blood pressure. It's usually better to take several readings to see what your blood pressure is normally like over time. If the readings are persistently high on most or all occasions, it indicates that you have high blood pressure.

The two numbers in a blood pressure value are called the systolic and diastolic. The systolic pressure is the blood pressure whilst the heart is contracting (pumping), and the diastolic pressure is the blood pressure whilst the heart is relaxing in-between heartbeats.

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.

• Both - for example, 170/110 mm Hg.

See the separate leaflet called High blood pressure (Hypertension).

What causes high blood pressure?

In most cases, there is no clear single cause of high blood pressure. This is called essential hypertension. There are probably multiple different factors causing a raised blood pressure, and these differ from person to person.

Blood pressure depends on how hard the heart pumps, and how much resistance there is in the blood vessels (arteries).

It's thought that people with hypertension develop slightly narrower and stiffer arteries, which increases the resistance to blood flow and therefore increases blood pressure. There may also be problems with the way the body handles water and sodium (salt), leading to too much salt and water being kept in the blood. This can slightly increase the volume (amount) of blood in the body, contributing to high blood pressure.

The reasons for this happening are very complicated and not fully understood.

Diabetes itself can be a cause of high blood pressure. Diabetes can cause damage to the kidneys (see Diabetic kidney disease, below), which affects their ability to control the balance of salt and water in the body, leading to high blood pressure. It can also cause the walls of blood vessels to stiffen over time.

The following things are also linked to high blood pressure:

• Genetics. Having a family history of high blood pressure means you're more likely to develop it yourself.

• Ethnic background. In the UK, people from African, Caribbean, or South Asian backgrounds are more likely to develop high blood pressure.

• Diet, especially eating high-salt foods.

• Older age.

• Overweight or obesity.

• Not being physically active.

• Drinking too much alcohol.

Diabetic kidney disease

Diabetic kidney disease (diabetic nephropathy) is a complication which develops in some people with diabetes. In this condition the kidneys are damaged, which can cause high blood pressure. This is more common in people with type 1 diabetes.

High blood pressure makes diabetic kidney disease worse, which is why it's particularly important to spot them both early, and keep high blood pressure under control.

Rarely, high blood pressure is caused by other conditions. It is then called secondary hypertension. For example, certain kidney or hormonal problems can cause high blood pressure.

Do I need any tests?

If you are diagnosed as having high blood pressure (hypertension) you are likely to be examined by your doctor and have some routine tests which include:

• A urine test to check whether you have protein or blood in your urine.

• A blood test to check your kidney function and to check your cholesterol level.

• A heart tracing (electrocardiogram, or ECG).

The purpose of the examination and tests is to:

• Rule out (or diagnose) a secondary cause of high blood pressure.

• Check to see if the high blood pressure has affected the heart.

• Check whether you have other risk factors such as a high cholesterol level.

Several of these tests are ones that are routinely done anyway if you have diabetes, even if you do not have high blood pressure.

Why is high blood pressure a problem?

High blood pressure (hypertension) is a major risk factor for developing a cardiovascular disease (such as a heart attack or stroke) and kidney damage, sometime in the future.

High blood pressure is usually not a problem in the short term, but if not controlled, over the years it can have a damaging effect on blood vessels (arteries) and put a strain on your heart.

In general, the higher your blood pressure, the greater your health risk. However, high blood pressure is just one of several possible risk factors for developing a cardiovascular disease.

Other risk factors that also increase the risk of developing a cardiovascular disease are:

• Lifestyle risk factors that can be prevented or changed:

  • Smoking.

  • Lack of physical activity (a sedentary lifestyle).

  • Obesity.

  • An unhealthy diet.

  • Excess alcohol.

  • High cholesterol blood level.

  • High fat (triglyceride) blood level.

• Diabetes.

• Kidney diseases that affect kidney function.

• 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 furring or 'hardening' of the arteries (atheroma).

• Ethnic group. For example, people who live in the UK, with ancestry from India, Pakistan, Bangladesh or Sri Lanka, have an increased risk.

You might notice that these have a lot in common with risk factors for high blood pressure.

Diabetes plus high blood pressure is a particularly strong combination of risk factors.

In addition, some other complications of diabetes are more common if you have high blood pressure. For example, damage to the back of the eye (diabetic retinopathy) and kidney damage related to diabetes (diabetic nephropathy).

What are the benefits of lowering blood pressure?

There is now plenty of good evidence from studies that controlling blood pressure in people with diabetes reduces the risk of future complications.

A large research study called the UK Prospective Diabetes Study confirmed this. In this study, many people with diabetes were monitored over several years. The study found that those with well-controlled blood pressure had nearly a third less risk of dying from complications related to diabetes (heart attack, stroke, etc) compared with those with poorly controlled blood pressure.

In fact, this study found that good control of blood pressure was even more beneficial than good control of the blood sugar (glucose) level to reduce the risk of developing complications from diabetes.

Since this study, other studies have been undertaken which confirm these results.

How can blood pressure be lowered?

There are two ways in which blood pressure can be lowered:

• Modifications to lifestyle (weight, exercise, diet, salt, and alcohol) if any of these can be improved upon (details below).

• Medication (details below).

Lifestyle treatments to lower high blood pressure

• Lose weight if you are overweight:

  • Losing some excess weight can make a big difference.

  • Blood pressure can fall by up to 2.5/1.5 mm Hg for each excess kilogram which is lost.

  • Losing excess weight has other health benefits too.

• Regular physical activity:

  • If possible, aim to do some physical activity on five or more days of the week, for at least 30 minutes. For example, brisk walking, swimming, cycling, dancing, etc.

  • Regular physical activity can lower blood pressure in addition to giving other health benefits.

  • If you previously did little physical activity and change to doing regular physical activity five times a week, this can reduce your blood pressure.

• Have a low salt intake:

  • The amount of salt that we eat can have an effect on our blood pressure. Government guidelines recommend that we should have no more than 6 grams of salt per day. (Most people currently have more than this.)

  • Tips on how to reduce salt include:

    • Use herbs and spices rather than salt to flavour food.

    • Limit the amount of salt used in cooking and do not add salt to food at the table.

    • Choose foods labelled 'no added salt' and avoid processed foods as much as possible.

    • Low-sodium salt substitutes can be used instead of regular salt. These contain potassium instead of sodium. However, these can be unsafe in some people with kidney problems, and in people taking certain medications (such as ACE inhibitors, which are often used in people with diabetes) - ask your doctor first before using them.

• Eat a healthy diet

  • If you have diabetes you will normally be given plenty of advice about a healthy diet.

  • A healthy diet provides health benefits in different ways. For example, it can lower cholesterol and help control your weight. It also has plenty of vitamins, fibre and other nutrients which help to prevent certain diseases. See the separate leaflet called Type 2 diabetes diet.

• Drink alcohol in moderation:

  • Too much alcohol can be harmful and can lead to an increase in blood pressure.

  • You should not drink more than the recommended amount. That is for both men and women no more than 14 units of alcohol per week, spreading the units out through the week and having at least two alcohol-free days a week.

  • Pregnant women and women trying to become pregnant should not drink alcohol at all.

  • One unit is in about half a pint of normal-strength beer, or two thirds of a small glass of wine, or one small pub measure of spirits.

  • Cutting back on heavy drinking improves health in various ways, including lowering your blood pressure.

Treatment with medication

• If you have diabetes, treatment with medicines is usually advised if your blood pressure remains at 140/90 mm Hg or above despite lifestyle treatments.

• People with diabetes and certain types of kidney problems may be advised to aim for a lower target of 130/80 mm Hg.

• Blood pressure targets are generally a little higher for people over 80 (usually 150/90 mm Hg), although doctors might recommend different levels depending on the exact situation.

There are several different medicines that can lower your blood pressure. The one chosen depends on such things as:

• Whether you have other medical problems.

• Whether you take other medication.

• Possible side-effects of the medicine.

• Your age.

The first medicine most often used is a medicine called an angiotensin-converting enzyme (ACE) inhibitor. ACE inhibitors protect against kidney damage as well as helping to control blood pressure. See the separate leaflet called Diabetic kidney disease.

One medicine reduces high blood pressure to the target level in less than half of cases. This therefore means that it is common to need two or more different medicines to reduce your blood pressure to a target level (140/80 mm Hg or below).

In about a third of cases, three medicines or more are needed to get blood pressure to the target level. See the separate leaflet called Medicine for high blood pressure.

How long is medication needed for?

In most cases, medication is needed for life. However, in some people whose blood pressure has been well controlled for a period of time, medication may be able to be stopped. In particular, in people who have made significant changes to their lifestyle (such as lost a lot of weight, stopped heavy drinking, etc). Your doctor will be able to advise you if you can reduce any of your medication.

Smoking and high blood pressure

Smoking causes an immediate rise in blood pressure, which starts to return to normal about 20 minutes after having a cigarette.

The links between smoking and longer-term blood pressure are not fully understood. Different studies have found different things. Overall, the evidence suggests that smoking does not seem to cause long-term high blood pressure, and stopping smoking doesn't seem to affect blood pressure control.

But we do know that smoking is very harmful to the heart, and is a major risk factor for developing heart disease and strokes. The combination of smoking, high blood pressure, and diabetes increases this risk significantly. Stopping smoking has many health benefits. If you smoke, you should make every effort to stop.