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What causes a stroke?

Stroke is a largely preventable event. 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 1 in 4 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.
  • Gender strokes are more common in men.
  • Your medical history  if you have previously had a stroke, transient ischaemic attack (TIA) or heart attack, your risk of stroke is higher.

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

Ischaemic strokes

Ischaemic strokes, the most common type of stroke, occur when blood clots block the flow of blood in the arteries 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:

Medical conditions such as insulin resistance, diabetes and chronic kidney disease are also risk factors.

An irregular heartbeat (atrial fibrillation) is another possible cause of ischaemic stroke since it can cause blood clots that become lodged in the brain. Atrial fibrillation may be due to:

  • 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).

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 developing high blood pressure include:

  • drinking excessive amounts of alcohol 
  • smoking
  • a lack of exercise 
  • stress, which may cause a temporary rise in blood pressure.
  • having a family history of high blood pressure
  • growing older
  • being overweight
  • having diabetes
  • having too much salt in the diet

Haemorrhagic stroke can also be caused by an aneurysm (the expansion and rupture of a blood vessel) or by badly formed blood vessels within the brain.

Treatment with medicines prescribed to prevent blood clots, such as warfarin, increases the risk of haemorrhagic stroke. However, do not stop taking any medication without first discussing it with your doctor.

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.

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 2017

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