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What causes a stroke?

Stroke is a largely preventable condition. Many risks can be reduced by making lifestyle changes.

However, some things that increase the risk of stroke cannot be changed, including:

  • Age  you are more likely to have a stroke if you are over 65 years old, although about one-quarter of strokes happen in younger people.
  • Family history  if a close relative (parent, grandparent, brother or sister) has had a stroke, your risk is likely to be higher.
  • Your medical history  if you have previously had a stroke, transient ischaemic attack (TIA) or heart attack, your risk of stroke is higher.

Ischaemic strokes

Ischaemic strokes, the most common type of stroke, occur when blood clots block the flow of blood to the brain. Blood clots typically form in areas where the arteries have been narrowed or blocked by fatty cholesterol-containing deposits known as 'plaques'. This narrowing of the arteries is caused by atherosclerosis.

As we get older our arteries become narrower, but certain things can dangerously accelerate the process. These risks include:

Diabetes is also a risk factor, particularly if  poorly controlled, as the excess glucose in the blood can damage the arteries.

Another possible cause of ischaemic stroke is an irregular heartbeat (atrial fibrillation), which can cause blood clots that become lodged in the brain. Atrial fibrillation can be caused by:

  • high blood pressure 
  • coronary artery disease 
  • mitral valve disease (disease of the heart valve) 
  • cardiomyopathy (wasting of the heart muscle) 
  • pericarditis (inflammation of the bag surrounding the heart) 
  • hyperthyroidism (overactive thyroid gland)
  • excessive alcohol intake 
  • drinking lots of caffeine, for example, tea, coffee and energy drinks.

Haemorrhagic strokes

Haemorrhagic strokes (also known as 'cerebral haemorrhages' or 'intracranial haemorrhages') usually occur when a blood vessel in the brain bursts and bleeds into the brain (intracerebral haemorrhage). In about 5% of cases, the bleeding occurs on the surface of the brain (subarachnoid haemorrhage).

The main cause of haemorrhagic stroke is high blood pressure (hypertension), which can weaken the arteries in the brain and make them prone to split or rupture.

Things that increase the risk of high blood pressure include:

  • drinking excessive amounts of alcohol 
  • smoking
  • a lack of exercise 
  • stress, which may cause a temporary rise in blood pressure.

Another important risk of haemorrhagic stroke is treatment with medicines given to prevent blood clots, such as warfarin.

Haemorrhagic stroke can also occur from the rupture of a balloon-like expansion of a blood vessel (aneurysm) and badly formed blood vessels in the brain.

A traumatic head injury can also cause bleeding into the brain. In most cases, the cause is obvious but bleeding into the lining of the brain (subdural haematoma) can occur without any obvious signs of trauma, especially in the elderly. The symptoms and signs can then mimic a stroke.

If you suspect that you or someone else is having a stroke, call triple zero (000) immediately and ask for an ambulance.

Source: NHS Choices, UK (Stroke - Causes)

Not sure what to do next?

If you are still concerned about what causes a stroke, why not use healthdirect’s online Symptom Checker to get advice on when to seek medical attention.

The Symptom Checker guides you to the next appropriate healthcare steps, whether it’s self care, talking to a health professional, going to a hospital or calling triple zero (000).

Last reviewed: July 2015

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