Stroke - Risk factors

In general, the risk factors for having an ischaemic stroke Any sudden neurological problem caused by a bleed or a clot in a blood vessel. - a stroke that is caused by a blockage in an arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. supplying the brain - may be divided into those that can be modified (improved upon), and those that cannot, as discussed below.

Although some risk factors cannot be changed - for example, a person's gender or age - it is still important to be aware of them. This is because people who have a number of unmodifiable risk factors may benefit from making a greater effort to improve those risk factors that can be modified.

In addition to these risk factors, which are often classed as 'traditional', we are also starting to learn about more recently identified risk factors.

Some of the risk factors for a haemorrhagic stroke Any sudden neurological problem caused by a bleed or a clot in a blood vessel. - a stroke caused by a bleed - differ from those of an ischaemic stroke and so are looked at separately.

Ischaemic stroke risk factors

Modifiable risk factors

Fortunately, we do have control over many of the risk factors for ischaemic strokes. These include the following:[1,2,3-7]

  • High blood pressure The pressure of blood within the arteries.- the most important modifiable risk factor for stroke Any sudden neurological problem caused by a bleed or a clot in a blood vessel. [4-6]
  • Smoking - this can contribute to atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow. and can also cause the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. vessels to constrict, which leads to restrictions in bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. flow. The associated risk increases with the number of cigarettes smoked per day, and passive smoking also increases this risk[6]
  • Excessive alcohol intake
  • Obesity, unhealthy diet (including a low fruit and vegetable intake and a high salt intake)
  • Physical inactivity
  • Abnormal lipidOne of a group of compounds that are an important energy source. levels (dyslipidaemiaAbnormal levels of lipids (fats) in the blood.)
  • Diabetes mellitus (associated with stroke and other forms of vascular disease at a younger than average age)[6] and metabolic syndromeThe combination of insulin resistance, abdominal obesity, high blood pressure and disordered blood lipids that increases the risk of cardiovascular disease.
  • Carotid arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. disease
  • Atrial fibrillation, an abnormal heart rhythm
  • Patent foramen ovaleThe opening between the two upper chambers (atria) of the heart of the fetus, which normally closes at birth. The term 'foramen ovale' may also be used to describe the large hole at the base of the skull. (otherwise known as a 'hole in heart') - present in around 25 per cent of the general population, compared with 40 per cent of people who have had a stroke where no other cause is found[8]
  • Heart failure, endocarditisInflammation of the inner lining of the heart and the heart valves. and other forms of heart disease
  • Oral contraceptives - thought to increase the likelihood of the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. to clot[9]
  • Polycythaemia, a condition in which the red bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cellThe basic unit of all living organisms. count is increased
  • Sleep apnoea, which causes interruptions in breathing while a person sleeps and appears to be associated with a higher risk of stroke and other cardiovascular diseases[10]
  • Sickle cellThe basic unit of all living organisms. disease, an inherited condition that results in the formation of abnormal, sickle-shaped red bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells that can block small bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. vessels, increasing the risk of an ischaemic stroke.[7] There is insufficient evidence to support the suggestion that sickle cell traitA condition in which the gene for sickle cell disease is inherited from just one parent rather than both. It is not usually associated with any symptoms. - a milder version of the disease - might also increase the risk.[11]

It is thought that excessive alcohol intake may also increase the risk of ischaemic stroke by bringing about a rise in bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. pressure. However, although drinking too much alcohol is known to inflate the risk, people who consume moderate amounts (less than 3 units per day) actually have a lower risk than those who do not drink at all. This may be because moderate alcohol intake can improve bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. lipidOne of a group of compounds that are an important energy source. levels, and so protect against vascular diseases such as stroke.[2]

Non-modifiable risk factors

Risk factors for stroke that cannot be modified include the following:[1,4-7]

  • Male gender
  • Older age
  • Family history
  • Past heart attackThe death of a section of heart muscle caused by an interruption in its blood supply. Also called a myocardial infarction. or stroke
  • Ethnicity.[16]

It has also been suggested that migraine may increase the risk of an ischaemic stroke, particularly in women under the age of 35. Migraine with aura (in other words, migraine accompanied by additional symptoms such as visual disturbance and numbness or tingling) is associated with reduced bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. flow to the brain and inflammationThe body’s response to injury..[12]

Transient ischaemic attack, or TIATransient ischaemic attack; any neurological problem caused by an interruption in the blood supply to the brain that resolves within 24 hours., is often referred to as a 'mini-stroke'. Like a stroke, it is a disturbance in the function of the nervous system that is caused by a problem with the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. supply to the brain. However, unlike stroke, the symptoms of TIATransient ischaemic attack; any neurological problem caused by an interruption in the blood supply to the brain that resolves within 24 hours. settle down within 24 hours.

People who have had a TIATransient ischaemic attack; any neurological problem caused by an interruption in the blood supply to the brain that resolves within 24 hours. are known to have a higher risk of a stroke in the future. The chance of someone who's had a TIATransient ischaemic attack; any neurological problem caused by an interruption in the blood supply to the brain that resolves within 24 hours. having a stroke within 3 months has been estimated to be between 15 and 20 per cent.[13]

Conditions that increase the likelihood of the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. to clot also increase the risk of stroke; examples include Factor V LeidenA change in the gene for Factor V, one of the coagulation factors. mutationA change in the genetic material (DNA) of a cell, or the change this this causes in a characteristic of the individual, which is not caused by normal genetic processes. [7] and Hughes syndromeAlso known as antiphospholipid syndrome. A type of autoimmune disease, caused by overactivity of the immune system. It is associated with thrombosis and, in women of childbearing age, recurrent miscarriage. (also known as antiphospholipid syndromeAlso known as Hughes syndrome. A type of autoimmune disease, caused by overactivity of the immune system. It is associated with thrombosis and, in women of childbearing age, recurrent miscarriage.), although these risks may be reduced by taking anticoagulantA medication that prevens blood from clotting, or which reduces the likelihood of the blood to clot. treatment.[14]

Recently identified risk markers

Additional markers (indicators) associated with an increased risk of ischaemic stroke include elevated levels in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. of:[11]

  • Homocysteine (a marker that is associated with early-onset atherosclerosisDisease leading to fatty deposits in the inner walls of the arteries, which reduce and may eventually obstruct blood flow.)
  • Lipoprotein(a) (a type of lipidOne of a group of compounds that are an important energy source. in the bloodstream that is similar to LDL-cholesterolSubstance that carries cholesterol around the bloodstream, a form of so-called 'bad cholesterol'.)
  • High-sensitivity C-reactive proteinA protein found in the blood. Raised levels suggest tissue damage or necrosis (death of cells). (CRPAn abbreviation for C-reactive protein, found in the blood. Raised levels of this protein suggest tissue damage or necrosis (death of cells).; a protein in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. that suggests inflammationThe body’s response to injury.)
  • High bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. levels of fibrinogenA coagulation factor, a substance in the blood that brings about clotting. (a protein that helps the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. to clot)
  • Apolipoprotein B (APOB; the protein part of low-density lipoproteinOne of a group of compounds that consist of a protein combined with a lipid, and help to transport lipids in the blood and lymphatic system. (LDL).[15]

Haemorrhagic stroke risk factors

Modifiable risk factors

Those risk factors for haemorrhagic stroke that we can improve upon include:

  • High blood pressure The pressure of blood within the arteries.- one of the most important modifiable risk factors for stroke[1,2,7]
  • Impaired ability of the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. to clot due to medication ('anti-clotting' drugs, anticoagulants; or 'clot-busting' drugs, thrombolyticsA medication that breaks up blood clots.)[1,7]
  • Smoking, excess alcohol intake and substance misuse (for example, amphetamines and cocaineA narcotic drug extracted from coca leaves.)[7]
  • Lipid levels. Unlike ischaemic strokes, it seems that reducing cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. levels actually increases the risk of haemorrhagic strokes[7]
  • Vascular malformations. These may include arteriovenous malformations, cavernous haemangiomas and aneurysms (an aneurysmAn abnormal swelling in the wall of an artery. is an abnormal dilation, or bulge, in the wall of an arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood..) Vascular malformations are prone to rupture.[1,7] Fortunately, they can sometimes be treated with surgery to reduce the risk
  • Conditions that interfere with bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. clotting, for example, blood dyscrasiaAn abnormal condition of the blood. (an abnormality in the balance of the different components of the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.).[1,7] Treatment may lower the risk.

Non-modifiable risk factors

The risk factors for haemorrhagic stroke that cannot be modified include the following:

  • Increasing age. This may be partly because older age is associated with small bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. vessel disease, which can increase the risk of bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. vessel rupture.[1,2] Increasing age also increases the likelihood of the condition amyloidA compound similar to starch, which can build up abnormally in the tissues in a condition called amyloidosis. angiopathyDisease of the blood vessels., which leads to protein build-up in the arteries of the brain, increasing the risk of bleeding[1,7]
  • Ethnicity.[7]

Symptoms similar to a stroke can also sometimes arise as a result of damage to bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. vessels in the brain following a head injury.

References: 
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