Modifiable risk factors (medical)
Hypertension (high blood pressure)
Hypertension is the most important modifiable medical risk factor. People with high blood pressure have a risk of stroke 4 to 6 times greater than those with normal blood pressure.
Blood pressure is normally expressed in terms of an upper reading (the systolic blood pressure) and a lower reading (the diastolic blood pressure) e.g. 120/80.
A systolic blood pressure of between 120 and 139 and a diastolic blood pressure of between 80 and 89 are considered to be within the normal range for adults by the British Hypertension Society. Sustained blood pressure of 140 over 90 or greater leads to the diagnosis of high blood pressure.
Reducing raised blood pressure to normal levels decreases a person’s risk for stroke by about one third, and reduces the fatality rate by 40 percent.
Commonly used drugs, which reduce blood pressure (anti-hypertensive agents) are:
- Angiotensin converting enzyme (ACE inhibitors)
- Beta-blockers
- Calcium channel blockers
- Diuretics
Heart disease
Heart disease is the second most important risk factor for stroke following hypertension, in particular a form of heart disease known as atrial fibrillation. This occurs where the upper chambers of the heart – the atria – beat irregularly and up to 4 times faster than the rest of the heart. This causes an irregular and turbulent flow of blood through the heart, which may lead to the formation of blood clots that can leave the heart and travel to the brain causing a stroke.
People with atrial fibrillation have a risk of stroke 4 to 6 times greater than those without this condition. As a person enters the upper age groups, atrial fibrillation becomes more common. In people 80 years of age and over, atrial fibrillation is the direct cause of 1 in 4 strokes.
Other forms of heart disease that increase the risk of stroke are:
- disease or malformations of heart valves (valvular heart disease) e.g. mitral stenosis
- malformations of heart muscle e.g. hole in the heart
Cardiac surgery also increases the risk of stroke by about 1 percent. This is usually due to dislodged plaques from the aorta (the main artery leaving the heart) travelling to the head and neck and ultimately to the brain.
Hyperlipidaemia and Cholesterol
High blood cholesterol levels are known to contribute to heart disease; however they also increase the risk of stroke.
Blood cholesterol is measured in millimoles per litre (mmol/l). The current recommendation is that an ideal blood level is below 5 mmol/l.
Stroke risk may be reduced by lowering cholesterol levels. This is best achieved by a healthy diet and regular exercise. Medication may be prescribed to lower cholesterol, usually in the form of drugs known as statins. These significantly reduce the risk of stroke in most people with high cholesterol.
Diabetes
People with diabetes mellitus have a risk of stroke that is 3 times greater than those without diabetes. This risk is at its greatest in the 5th and 6th decades of life, and decreases after that.
People with diabetes may also have other contributing risk factors thereby increasing the risk of stroke. Hypertension, for example is 40 percent more prevalent in the diabetic population than in the general population.
People with diabetes not only have a higher death rate from strokes than the general population, they also have more severe disability and recover more slowly. This has been linked to a larger degree of brain damage and higher frequency of recurrent stroke.
Controlling hypertension and reducing cholesterol levels has been shown to be very effective in reducing the incidence of strokes in people with diabetes.
