Transient ischaemic attacks (TIAs) happen when one of the blood vessels that supply your brain with oxygen-rich blood becomes blocked. This interruption in the flow of blood to the brain means it cannot do some of its normal functions properly, leading to symptoms such as slurred speech and weakness.

In TIAs, the blockage quickly resolves and your brain's blood supply returns to normal before there's any significant damage. In a full stroke, the blood flow to your brain is disrupted for much longer, leading to more severe damage to the brain and longer-term problems. The blockage in the blood vessels responsible for most TIAs is usually caused by a blood clot that's formed elsewhere in your body and travelled to the blood vessels supplying the brain. It can also be caused by pieces of fatty material or air bubbles.

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

Blood clots

Blood clots that cause TIAs may form in areas where arteries have been narrowed or blocked over time by the build-up of fatty deposits known as plaques. These plaques are formed during a process called atherosclerosis.

As you get older, your arteries can naturally become narrower, but certain things can dangerously speed up this process. These include:

• smoking
• high blood pressure (hypertension)
• obesity
• high cholesterol levels
• diabetes
• excessive alcohol consumption

A type of irregular heartbeat called atrial fibrillation can also cause a TIA. It can lead to the formation of blood clots that escape from the heart and become lodged in the blood vessels supplying the brain.

Who's most at risk?

Certain things can increase your chances of having a TIA. Some of these factors are changeable – such as your lifestyle. Some of the main risk factors for TIA are:

• age – although TIAs can happen at any age (including in children and young adults), they're most common in people over 55
• ethnicity – people of south Asian, African or Caribbean descent have a higher TIA risk, partly because rates of diabetes and high blood pressure are higher in these groups
• medical history – other health conditions such as diabetes can increase your risk of a TIA
• weight and diet – your risk of having a TIA is higher if you're overweight or have an unhealthy diet high in fat and salt
• smoking or alcohol – smoking or regularly drinking excessive amounts of alcohol can increase your TIA risk

Tackling the things you can change will help to lower your risk of having a TIA, or reduce your chances or having a full stroke in the future.