Several factors usually work together to increase the chances of a stroke. The risk factors for the various types of stroke are slightly different. Medical conditions like high blood pressure and diabetes may act together with ageing and an unhealthy lifestyle to cause strokes.
Most of these risk factors can lead to disease in other parts of the body as well and can cause conditions such as heart attacks.
Exceptionally, younger patients with no obvious risk factors may have strokes and doctors then have to carry out several tests to try and understand the underlying cause.
Here is a brief description of known risk factors.
The risk of getting a stroke rises with age. In fact, age is the strongest risk factor for stroke with the risk of an ischaemic stroke in an 80 year old being 30 times that of the risk in a 50 year old.
However, no age is spared and strokes can occur in the very young.
Middle aged or elderly men are at slightly higher risk of getting a stroke. This effect is not as strong as that for heart attacks and in the very elderly or young patients, men and women have similar risks.
Afro-Caribbean and South Asian people seem to have a slightly higher risk of strokes. This may be because of higher blood pressure or higher rates of diabetes.
Does stroke run in famliies?
Some families seem to have a greater risk of strokes and heart attacks because of an inherited predisposition to high levels of cholesterol and high blood pressure.
However, interaction between genes and the environment (i.e. fat and salt consumption or smoking) are important for most strokes. Some rare causes of strokes such as aneurysms may be inherited.
High blood pressure (hypertension)
Stroke risk is strongly related to high blood pressure. Hypertension damages blood vessels in the brain and other parts of the body. It damages the small blood vessels in the brain and causes atheroma in larger arteries. It causes both infarcts and haemorrhages.
High blood pressure affects 1 in 4 adults and if undetected or uncontrolled is the most important cause of strokes. The risk of strokes in people with untreated hypertension is about seven times greater than that in people with normal blood pressures.
The blood pressure is expressed as two numbers e.g. 120/80; the upper number is the systolic blood pressure and the lower the diastolic.
Both these readings are important and elevation of either the systolic, diastolic or both of these pressures is dangerous. Because people with high blood pressure do not usually have any symptoms before they run into complications, the only way of detecting hypertension is a periodic check up at the doctors.
Treatment of high blood pressure begins with with sensible lifestyle advice such as cutting down salt intake, having a healthy diet with plenty of fruits and vegetables, regular exercise, weight loss, smoking cessation and avoiding excess alcohol. The treatment of high blood pressure often involves taking several drugs (anti-hypertensives) as these drugs work in different ways and have additive effects.
These drugs are effective only as long as they are taken and if they are stopped, the blood pressure will rise again. The usual target for treatment is to lower the blood pressure to less than 140/85. In people who have already had a stroke, the aim is to lower the blood pressure even further.
Doctors are not yet sure if it is necessary to lower the blood pressure in extreme old age as there is not enough information available about the importance of hypertension in that age group. More information is available from the British Heart Foundation.
Smoking causes a 2 -3 fold increases in the risk of a stroke and about 1 in 4 strokes can be directly attributable to smoking. The risk increases with higher cigarette consumption.
Cigar and pipe smoking is also suspected to cause strokes though the risk is greater for causing heart attacks.
Cigarette smoke contains substances that constrict blood vessels, promotes the deposition of atherosclerotic plaques and makes the blood thicker and more prone to clot.
It has been suggested that half of all smokers may die as a result of smoking. It is estimated that between 1998 and 2002, smoking caused an average of 86,500 deaths a year in the UK.
The good news is that the risk of strokes declines greatly within two - five years of quitting.
Find out more about the support on offer in Gloucestershire for smoking cessation.
Diabetes doubles the risk of ischaemic stroke and diabetics who have a stroke often have worse outcomes than non diabetics. High blood sugar at the time of a stroke can cause the stroke to become more severe.
Atrial fibrillation is a common disturbance of the rhythm of the heart. It leads to an irregular heart beat which may be intermittent (paroxysmal atrial fibrillation) or persistent.
With this condition, clots can form within the heart and travel in the circulation to cause obstruction of blood flow in different parts of the body. If a clot blocks an artery in the brain, a stroke or TIA can result.
Depending on other factors, the risk of a stroke with atrial fibrillation can be very high; as much as 5-12% per year. It is possible to calculate the risk for any patient and high risk patients are offered treatment with warfarin (an anticoagulant) to thin the blood down.
Warfarin is more effective than aspirin in moderate to high risk patients with atrial fibrillation. Angina and heart attacks are related to strokes. Patients with recent heart attacks are at higher risk of a stroke because clots can break off in the heart and cause a stroke.
Most of the risk factors for heart attacks and strokes are common, so it is not surprising that people with ischaemic heart disease are at risk of stroke. Patients who have had strokes and TIAs are also at risk of having heart attacks.
Diseases of heart valves such as narrowing, particularly of the mitral valve increases the risk of strokes especially if the patient also has atrial fibrillation.
Heart failure and left ventricular hypertrophy increase the risk of strokes. Heart failure is a condition where the heart is weak and does not pump blood as strongly as expected. Left ventricular hypertrophy is an abnormal thickening of the walls of the main chamber (left ventricle) of the heart.
TIA, previous strokes and cartoid artery disease
People who have had a transient ischaemic attack (TIA) have a seven times higher risk of having a stroke as compared to a person of the same age and sex without a TIA.
The risk of a stroke in the first year after a TIA is about 10%. Thereafter the risk falls to about five percent a year but remains elevated for several years.
The risk of a stroke after a TIA is highest in the first few days, hence a TIA is a medical emergency and an urgent medical assessment is needed. People who have had a TIA are also at higher risk of having a heart attack with rates of about thee-five percent a year.
People who have had a stroke have an almost ten times higher risk of having another stroke. They are also at risk of having heart attacks.
Narrowing of the carotid arteries (the main arteries in the neck) due to atherosclerosis is an important risk factor for strokes. Severe narrowing (stenosis) of about 70% or above is considered to be a critical level beyond which an operation called carotid endarterectomy is helpful in patients who have had a recent TIA or minor stroke.
In patients with severe stenosis who have had a recent TIA or minor stroke, the risk of a further stroke is about 10-14% a year. The risk is highest in the first 2 years and then fall rapidly.
For those with severe carotid stenosis who have not had any TIA or strokes (asymptomatic stenosis) , the risk of a stroke is much lower at about three percent a a year and the risks of an operation are considered to outweigh the benefits and hence surgery is not recommended.
High cholesterol levels (hyperlipidaemia, hypercholesterolaemia)
Increasing levels of cholesterol promotes atherosclerosis and is strongly related to causing heart attacks but the relationship with strokes is less clear.
However, research has shown that in people who have had a stroke, lowering the cholesterol with drugs called statins does cause a reduction in strokes as well as heart attacks.
It is sensible to have a healthy diet and reduce high levels of cholesterol with statins. More information is available from the British Heart Foundation.
Modest consumption of alcohol (up to about 2 small drinks a day) may actually protect against strokes.
Heavy alcohol consumption is a risk factor and can lead to strokes particularly cerebral haemorrhage by raising the blood pressure and causing blood vessels to burst.
Binge drinking is particularly harmful. British recommendations are up to two to three units of alcohol a day for women and three to four units for men. It's a good idea to have two or to three alcohol-free days each week.
One unit is 8g of alcohol. Often units are quoted as being one small glass of wine, half a pint of beer or one pub measure of spirits.
However, some stronger beers and lagers may contain as many as 2.5 units of alcohol per half pint. The size of some drinks may also vary; a large glass of wine may have 2 units of alcohol or more.
Read more about alcohol and drinking
Strokes and heart attacks are commoner in obese people. The exact mechanism is probably related to increased blood pressure, physical inactivity and higher rates of diabetes and hyperlipidaemia in overweight people.
The Body Mass Index or BMI is a way of assessing ideal body weight. Charts and calculators are available that can show the ideal weight for a person's height. Another useful measurement is the 'waist hip ratio' or a simple waist measurement.
A waist of 40 inches (102 cm) or more for men and 35 inches (89 cm) or more for women is considered dangerous.Whatever the method used, being overweight can contibute to the risk of a stroke and other disease.
Information on diets -
- Cut down on salt (leaflet)
- Reducing your blood cholesterol
- Healthy eating diet sheet
- So you want to lose weight (leaflet)
Find out more about healthy eating
Lack of exercise is associated with greater risk of strokes and heart attacks. Physical activity is beneficial because it reduces body weight, blood pressure, cholesterol and the risk of diabetes.
It also makes the blood less sticky. Beneficial exercise includes walking, running, swimming and other sports. The recommended level of exercise is 30 minutes at least 3 - 4 times a week.
Find out more about exercise
Is stress a cause of strokes?
There is some evidence that severe stress, anxiety, depression and anger may trigger off strokes in people who are already at high risk.
Oral contraceptive pill and hormone replacement therapy
The oral contraceptive pill does increase the risk of a stroke but the absolute stroke risk is still small and does not make routine pill use dangerous. However, people who are hypertensive, smoke or have other risk factors should not use the pill.
Over the years, there have been conflicting reports on HRT and strokes. It was believed earlier that HRT may even protect against strokes but more recently, the use of oestrogen alone or combined HRT has been associated with a higher risk of ischaemic stroke.
Hence it should not be used in women who have had a stroke.