Like all organs, the brain needs the oxygen and nutrients provided by blood to function properly.
If the supply of blood is restricted or stopped, brain cells begin to die. This can lead to brain injury, disability and possibly death.
There are 2 main causes of strokes:
ischaemic – where the blood supply is stopped because of a blood clot, accounting for 85% of all cases
haemorrhagic – where a weakened blood vessel supplying the brain bursts
There's also a related condition called a transient ischaemic attack (TIA), where the blood supply to the brain is temporarily interrupted.
This causes what's known as a mini-stroke. It can last a few minutes or persist up to 24 hours.
TIAs should be treated urgently, as they're often a warning sign you're at risk of having a full stroke in the near future.
Seek medical advice as soon as possible, even if your symptoms get better.
Certain conditions increase the risk of having a stroke, including:
high blood pressure (hypertension)
high cholesterol
irregular heart beats (atrial fibrillation)
diabetes