What is a stroke?

A stroke occurs when part of the brain is suddenly severely damaged or destroyed. It takes place either when a blood clot forms in a damaged vessel and blocks the flow of blood to part of the brain, or when a damaged vessel in the brain bursts. Without oxygen and nutrients, nerve cells in the brain will die within minutes. When this happens, the part of the body controlled by these cells will fail to function properly as well. The effects are often permanent.

Are there warning signs?

A major stroke is often preceded by a "warning stroke" called a TIA, or transient ischemic attack. This happens when a blood clot clogs an artery for a short time. The signs of a TIA are similar to those of a stroke, but usually last for just a few minutes.

What are the effects of a stroke?

Symptoms of minor episodes include temporary weakness or numbness in an arm or leg, and may precede a major stroke. Strokes can cause sudden weakness or complete paralysis of the muscles controlled by the part of the brain affected as well as sensory changes such as numbness or tingling. In the worst cases, these symptoms and signs may be accompanied by loss of consciousness. The patient may suffer slurring or loss of speech, difficulty swallowing, the mouth may droop, and there may be dribbling, headache, dizziness and confusion.

What are the causes?

The single most important risk factor is high blood pressure (hypertension) - which weakens the walls of arteries. This probably accounts for around 70% of all strokes. Hypertension can also speed up the blockage of the arteries (atherosclerosis). Strokes are often associated with:

• Diabetes
• Atrial fibrillation (irregular heart beat)
• High cholesterol
• High red blood cell count
• Heavy drinking
• Smoking
• Obesity
• The contraceptive pill

Who is affected?

Every year, about 100,000 people in the UK suffer strokes for the first time - 10,000 of them are under retirement age. Almost one in four men and nearly one in five women aged 45 can expect to have a stroke if they live to 85. Statistics show that the chances of having a further stroke in the first year are between one in six and one in ten. About a third of major strokes are fatal, a third result in some disability and a third have no lasting ill effects. Stroke is the third highest cause of death, and the largest cause of severe disability in England and Wales.

How can strokes be prevented?

Some factors that increase the risk of having a stroke are genetically determined and may be difficult to change. Others factors, however, result from a person's lifestyle and are more easily addressed.

Some experts claim that more than 2,400 strokes and 700 other cardiovascular events - mainly heart attacks - in England and Wales could be prevented or postponed by people taking aspirin, a cheap and simple treatment. However, aspirin does have some side-effects and should not be used by people who have had haemorrhagic strokes - caused by an artery bursting and damaging the brain around it.