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Epidemiological studies have identified many factors considered to increase the risk of stroke. Some risk factors can not be modified, but may serve as markers of increased risk. Other risk factors are capable of modification and are the basis of stroke prevention protocols.

The strongest determinant of stroke is age. The incidence of stroke rises with age nearly doubling every decade after age 55 and the majority of strokes occur in persons older than 65. As the population ages the number of stroke cases will become greater.

Stroke incidence is 1.25 times greater in men than women. However, women tend to live longer than men, therefore the prevalence of stroke may be greater among women.

The hereditability of cerebrovascular disease has been under-emphasized. Studies have found that a family history of stroke among first-degree relatives, a maternal history of death from stroke, and a paternal or maternal history of stroke are associated with an increased stroke risk.

Despite a decline in stroke mortality in all race-gender groups, the relative difference between races in stroke mortality has remained fairly uniform at nearly a two-fold increased stroke mortality in blacks compared with whites. Asians, particularly Chinese and Japanese, also have exceedingly high stroke incidence rates.

Major reductions in stroke morbidity and mortality are more likely to arise from identification and control of modifiable factors in the stroke-prone individual. Modifiable stroke risk factors include: hypertension, cardiac disease (particularly atrial fibrillation), diabetes, cigarette use, alcohol abuse, dyslipidemia, asymptomatic carotid stenosis, and transient ischemic attacks.

Table 1: Estimate of the Strength of Association of Various Modifiable Risk Factors for ischemic stroke:

Risk Factor	Relative Risk	Estimated Prevalence
Hypertension	3 - 5	25 - 40 %
Cardiac Disease	2 - 4	10 - 20 %
Atrial Fibrillation	5 - 18	1 1-2 %
Diabetes Mellitus	1.5 - 3	4 - 8 %
Cigarette Smoking	1.5 - 2.5	20 - 40 %
Heavy Alcohol Use	1 - 3	5 - 10 %
Dyslipidemia	1 - 2	6 - 40 %
Asx Carotid Stenosis	1 - 2	1 - 5 %

Because of its high prevalence, hypertension is the most powerful stroke risk factor after age. The risk of stroke rises proportionately with increasing blood pressure and even a slight improvement in the control of hypertension could translate into a substantial reduction in frequency of stroke.

Cardiac disease has been definitely associated with an increase in the risk of ischemic stroke. Cardiac factors which have been documented as independently increasing the risk of stroke include: atrial fibrillation, valvular heart disease, myocardial infarction, coronary artery disease, congestive heart failure, and electrocardiographic evidence of left ventricular hypertrophy.

Atherosclerosis and microangiopathy of the coronary, peripheral and cerebral arteries are frequently complications of diabetes. The relative risk of ischemic stroke ranges from 1.5 to 3.0 and probably depends on the type, duration and severity of the diabetes.

Cigarette smoking has been established as a biologically plausible, independent determinant of stroke. For different stroke types, the risk attributed to cigarette smoking was greatest for subarachnoid hemorrhage, intermediate for cerebral infarction, and lowest for cerebral hemorrhage.

The role of alcohol as a stroke risk factor is controversial. A J-shaped relationship between alcohol and stroke has been observed with an elevated risk for moderate to heavy alcohol consumption and a protective effect in light drinkers when compared with non-drinkers

Abnormalities in serum lipids, triglyceride, cholesterol, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) are regarded as risk factors, more for coronary artery disease than cerebrovascular disease. The absence of a consistent significant relationship between cholesterol and stroke may be partially explained by the recognition that there are multiple stroke subtypes which are not all attributed to atherosclerosis. Degree and progression of carotid atherosclerosis have been found to be directly related to cholesterol and LDL, and inversely related to HDL.

Asymptomatic carotid artery disease, which includes non-stenosing plaque or carotid stenosis, is frequent and increases with age, occurring in 53.6% of subjects 65 to 94 years of age. Among individuals with asymptomatic carotid disease, the annual stroke risk was 1.3% in those with stenosis of 75% or less, and 3.3% in those with stenosis of more than 75%, with an ipsilateral stroke risk of 2.5%.

Transient ischemic attacks are a strong predictor of subsequent stroke with annual stroke risks of 1% to 15%. The first year after a TIA is associated with the greatest risk.

Other potential stroke risk factors have been identified in some studies, but epidemiological studies failed to demonstrate that they are common significant risk factors: migraine, oral contraceptives, drug abuse, snoring, stress, patent foramen ovale, atrial septal aneurysm, mitral valve prolapse, spontaneous ECHO contrast

valve strands, aortic arch plaque, protein C & free protein S deficiencies, hyper-homocysteinemia, antiphopholipid antibodies, lupus anticoagulant, prothrombin fragment 1·2, factor V Leiden, , lipoprotein fractions (Lp(a)),

Risk factor modification may be attempted either through the "high risk approach" which identifies and seeks to modify the degree of risk in individuals with increased risk of disease, or through a "mass" approach which targets modification of risk factors detectable through the screening of large populations. It has been estimated that 246,500 strokes could be prevented in the USA by the control of hypertension alone and this would result in a saving of $12.33 billion. A program aimed against cigarette smoking could prevent over 61,000 strokes with an associated saving of over $3 billion in USA. Treatment of atrial fibrillation and modification of heavy alcohol use could eliminate 47,000 and 23,500 strokes, respectively in the USA.

Editors Note	SAGAS Objectives	SAGAS News	Stroke Risk Factors: An Overview
A Need For A World Stroke Federation	International Article Review	The Periodical Quiz	The Periodical Case

The Periodical Second Issue, November 2002