produce harmful by-products of metabolism known as free radicals which damage tissues, increasing the risk of atherosclerosis and also of cancer.
For more information, see Chapter 21.
OBESITY
People who are overweight or obese are more likely to have high blood pressure than thin people, as there is a larger body tissue mass through which the heart has to pump blood. Overweight people are also more likely to eat an unhealthy diet with a high intake of saturated fat. This raises blood fat levels, which in turn hastens the onset of atherosclerosis. Another factor is that overweight people tend to be inactive.
Although not everyone who is overweight has high blood pressure, however, there seems to be an interaction between obesity and some underlying, predisposing mechanism that is inherited by some people. This may be linked to where excess fat is stored. Overweight people who carry excess weight around their middle (apple-shaped) rather than around their hips (pear-shaped) seem to be at greater risk of a number of health conditions, including high blood pressure, atherosclerosis, raised cholesterol levels, diabetes, CHD and stroke. The reasons are not fully understood but may be linked to the way the body metabolizes dietary fats.
For more information, see Chapter 21.
ALCOHOL
A high alcohol intake is also linked with an increased risk of hypertension. People who regularly consume excessive amounts (more than 3 units of alcohol per day, or 21 units per week) tend to have higher blood pressures. However, many people drink more than this and have a normal blood pressure – it depends on whether you have inherited predisposing factors that make you sensitive to these effects of alcohol.
For more information, see Chapters 11 and 21.
LACK OF EXERCISE
Lack of exercise is an important cause of high blood pressure. Inactivity means the heart is unfit, despite having to work extra hard to pump blood around the increased bulk of the body. People who exercise for at least 20–30 minutes, three times per week, have a lower risk of high blood pressure, stroke, obesity and coronary heart disease than those who are physically inactive.
To be beneficial, exercise needs to be brisk enough to raise your pulse rate, produce a light sweat and to make you slightly breathless. Unfortunately, the average level of physical activity in the UK is low. Only 30 per cent of men and 20 per cent of women are active enough to gain some protection against high blood pressure. One survey among adult males found that one in five had taken no exercise at all during the preceding month. Although exercise increases the amount of blood pumped through the heart by up to 700 per cent, and puts BP up during the period of exercise itself, this is a healthy, temporary response.
Taking regular exercise helps to prevent high blood pressure by:
For more information, see Chapter 21.
STRESS
High blood pressure is thought to be linked with excessive levels of stress in some people. Susceptible individuals have an overactive part of the nervous system (sympathetic nervous system) which is unusually responsive to stressful stimuli that would normally be associated with only a mild, temporary rise in blood pressure. This overactivity of sympathetic nerves probably runs in families, with stress acting as the environmental factor that triggers off the process.
In people sensitive to stress, a condition known as Gaisbock’s syndrome can occur. This is a form of labile hypertension in which blood pressure levels can vary considerably. Sometimes they are high; sometimes they are low or normal. This can lead to more permanent hypertension if their lifestyle doesn’t slow down. One of the most common signs of this is so-called White Coat Hypertension – blood pressure that shoots up on being measured in the surgery or hospital (usually by someone wearing a white coat or uniform). This can increase systolic BP by as much as 100 mmHg, although this is extreme. More commonly, white coat hypertension increases systolic BP by 20–30 mmHg. This form of hypertension is confirmed by attaching the sufferer to a 24-hour BP monitoring tape and showing that BP rises in stressful conditions, including having BP measured by a doctor, then falls again in between.
Until recently, white coat hypertension was thought to be relatively harmless. However, latest research suggests that people with this condition have just as many abnormalities of the heart and blood vessels (e.g. poor left ventricular function, decreased elasticity and increased stiffness of artery walls) as those with persistently high blood pressure. They are also likely to develop hypertension in the future.
In most people, however, stress only causes only a transient rise in BP as a result of the hormone adrenaline (epinephrine). This triggers the constriction of arteries and veins which temporarily puts blood pressure up. This is an adaptive response to help you fight or flee in dangerous situations. Blood pressure can still fall when you are at rest or asleep, however, and relaxation training is usually helpful in offsetting the effects of excessive stress.
For more information, see Chapter 21.
KELOIDS
Interestingly, people who develop an excessive scar tissue reaction to a skin wound and produce a large, lumpy, keloid scar seem to be twice as likely to develop high blood pressure as people who produce normal amounts of scar tissue. This is thought to be due to a blood protein, angiotensin II, which helps to regulate blood pressure. It is now also known to stimulate production of collagen – a fibrous protein found in scar tissue. A group of drugs that block angiotensin (angiotensin converting enzyme – or ACE-inhibitors) are commonly used to treat high blood pressure. The link is the result of much research in an attempt to unravel some of the mysteries of essential hypertension.
For more information on dietary factors affecting essential hypertension, such as increased salt intake, and low intakes of calcium, magnesium, folic acid and antioxidants, see Chapters 6, 7, and 12.
Causes of Secondary Hypertension
One in ten people with hypertension have a recognizsed, underlying cause and are said to have secondary hypertension.
