Causes of a transient ischaemic attack 

During a transient ischaemic attack (TIA), one of the small blood vessels that supply your brain with oxygen-rich blood becomes blocked.

Blood is supplied to your brain by two main blood vessels (carotid arteries) and two other blood vessels (vertebral arteries). These arteries branch off into a series of smaller blood vessels that supply blood to every part of your brain.

If a blood vessel becomes blocked, the blood flow to your brain will be disrupted. In TIAs, the disruption quickly passes and your brain's blood supply soon returns to normal. In a full stroke, blood flow to your brain is disrupted for much longer. Without a constant supply of blood, your brain cells will begin to die.

The blockage in your blood vessels is usually caused by a narrowing of the arteries, or as a result of a blood clot that has formed elsewhere in your body and travelled to your brain.

Atherosclerosis

Atherosclerosis is a condition that causes narrowing of the arteries. It occurs when fatty deposits, known as plaques, develop on the inner lining of your blood vessels.

This can cause your blood vessels to become thickened, hard and less elastic, making it more difficult for blood to flow through them.

Read more about atherosclerosis.

Blood clots

A TIA can also occur when a blood clot develops in a blood vessel and blocks the blood supply to your brain.

Blood clots can be caused by a number of different factors including:

  • heart conditions  such as atrial fibrillation, which causes your heart to beat irregularly, or congestive heart muscle disease where your heart does not pump blood effectively 
  • blood conditions  such as leukaemia (cancer of the blood cells), sickle cell anaemia (an inherited blood disorder), high levels of fat in your blood (hyperlipidaemia), abnormally thickened blood (polycythaemia), or overproduction of platelets in your blood (thrombocythaemia)

A TIA can sometimes occur when a blood clot from a blood vessel in another part of your body moves into one of the arteries that supply blood to your brain. This is known as an embolism.

Haemorrhage

In very rare cases, a TIA can be caused by a small amount of bleeding in the brain. This is known as a haemorrhage.

Risk factors

A number of factors can increase your chances of having a TIA. These risk factors can either be:

  • fixed  such as age and gender
  • changeable  by altering your lifestyle, you may be able to reduce your risk of having a TIA

Some of the fixed risk factors associated with TIA are outlined below.

Age

As you get older, your arteries begin to harden and narrow, increasing your risk of having a TIA.

TIAs most commonly occur in people over 60 years of age, although they can occur at any age, including in children and young adults. 

Gender

Men have a higher risk of having a TIA compared with pre-menopausal women. The risk of having a TIA or stroke increases in post-menopausal women.

It is not fully understood why the risk of having a TIA increases following the menopause (when a woman's monthly periods stop). However, the female hormones, oestrogen and progesterone, are thought to play a role as they can affect elasticity of the blood vessels.

In menopausal women, oestrogen and progesterone levels fall, which may cause the blood vessels to become harder and less elastic. 

Ethnicity

As people of South Asian, African and Caribbean origin have an increased risk of developing high blood pressure and diabetes, they are also more at risk of having a TIA.

Family history

If you have a family history of stroke or TIA, your risk of having a TIA is increased. However, the risk is relatively small and having family members who have had a TIA will not necessarily mean that you will have one.

High blood pressure

High blood pressure (hypertension) is the most significant risk factor associated with TIA. Having high blood pressure puts extra strain on your body's blood vessels, causing them to become narrowed or clogged. 

Weight and diet

A diet high in saturated fat increases your risk of developing atherosclerosis. If there is too much salt in your diet, it is likely your blood pressure will be elevated which, like atherosclerosis, is a major risk factor for TIA.

Being overweight also puts your heart under strain and weakens your blood vessels. 

Smoking

Smoking can double your risk of having a TIA or stroke. The harmful chemicals in cigarette smoke cause the lining in the arteries to thicken, which makes your blood more likely to clot.

Therefore, stopping smoking (if you smoke) is one of the main ways of preventing a TIA or stroke.

Read about how to lower your risk of having a TIA.

Medical conditions

Certain medical conditions, such as type 1 diabetes and type 2 diabetes, can increase your risk of having a TIA.

Diabetes causes high levels of glucose to develop in your bloodstream, which increases your risk of developing atherosclerosis (see above).

Page last reviewed: 03/10/2012

Next review due: 03/10/2014