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Risk Factors for Stroke

Age

People of advanced age have a relatively high risk of stroke due to the cumulative effects of atherosclerosis and other related factors. However, over one-quarter of strokes happen in people under the age of 65 years.¹

Alcohol

The relationship between light alcohol intake and stroke is unclear. Having one or two drinks per day has lowered stroke risks in most studies,^2,^3,⁴ though some researchers report no protection⁵ and others find that even light drinking leads to an increased risk of stroke.⁶ Regular heavy drinking or binge drinking, however, raises the risk of suffering a stroke by increasing blood pressure and causing heart muscle dysfunction and other effects.^7,^8,⁹ People interested in the relationship between alcohol and stroke should discuss the issue further with a doctor and see the Alcohol section for a more complete discussion of the risks and benefits of alcohol consumption.

Antioxidant Supplements

Although eating fruits and vegetables, good sources of antioxidants, decreases the risk of stroke (see Fruits and Vegetables), the effectiveness of supplemental antioxidants is questionable. While earlier studies suggested a protective effect,^10,¹¹ recent reports have not found that people taking antioxidant supplements have a reduced risk of strokes.^12,^13,^14,¹⁵

Atrial Fibrillation

Atrial fibrillation is an irregular heart beat resulting from the quivering or uncontrollable contraction of the two small chambers of the heart. Atrial fibrillation is a significant risk factor for stroke, at least in people over the age of 60.¹⁶

People with atrial fibrillation are often given aspirin or anticoagulant medication to reduce blood clotting tendencies. Some natural inhibitors of blood clotting exist, such as garlic,^17,^18,¹⁹ fish oils,²⁰ and vitamin E.^21,²² However, even large amounts of fish oil are known to be less potent than aspirin,²³ and whether any of these substances would be adequate substitutes for controlling the risk of stroke due to atrial fibrillation remains unknown. Anyone taking anticoagulant medication should advise their prescribing doctor before beginning to use any of these natural substances.

Carotid Stenosis

Carotid stenosis is the medical term used to describe a narrowing of the main arteries that supplies the brain with blood. Carotid stenosis is caused by atherosclerosis— the same process that narrows arteries in the heart. People with carotid stenosis have an increased risk of both stroke and heart attack. By using a stethoscope, doctors can listen to carotid arteries at the point where they pass through the neck, providing diagnostic information. Special tests to evaluate stenosis in these arteries can also be ordered.

Elevated homocysteine levels in the blood have been linked to increased thickening of the carotid artery.²⁴ Homocysteine can be lowered with folic acid, vitamin B6, or vitamin B12. (See the High Homocysteine section for more information.) However, whether lowering of elevated homocysteine helps prevent carotid stenosis or stroke is unknown.

Preliminary studies have found that people who eat foods high in antioxidants such as vitamin C and vitamin E have less risk carotid stenosis.^25,²⁶ In a double-blind study, people with atherosclerosis in the carotid arteries were given a palm oil extract containing 160–240 mg tocotrienols (a vitamin E-like supplement) and approximately 100–150 IU vitamin E per day. After 18 months, they had significantly less atherosclerosis or at least less progression of atherosclerosis compared to a group receiving placebo.²⁷ Reducing carotid atherosclerosis should reduce the risk of suffering a stroke.

Cholesterol (High)

While high cholesterol levels increase heart disease risk, the relationship of cholesterol to stroke risk is less clear.²⁸ The risk of suffering the most common type of stroke, which is caused by blood clots, is increased by high cholesterol levels.²⁹ However, the risk of less common strokes caused by hemorrhage (bleeding) in the brain is increased in people with relatively low cholesterol levels,³⁰and a high serum cholesterol seems to be protective against this type of stroke.^31,^32,³³ Lowering total cholesterol levels should lower total risk for stroke, but research to date has been inconclusive.^34,³⁵ Higher levels of HDL ("good cholesterol") have been associated with protection against both the clot-type and the bleeding-type of stroke.

Diabetes Mellitus

Diabetes mellitus is a disorder characterized by high blood sugar levels. In type 1 (insulin-dependent) diabetes, the pancreas fails to produce sufficient insulin. In type 2 (non-insulin-dependent) diabetes, enough insulin is produced, but the body is resistant to the actions of insulin. People with diabetes, especially type 2, are at increased risk of stroke. However, having well-controlled or a milder degree of diabetes is less likely to increase the risk of suffering a stroke compared with having poorly-controlled or more severe diabetes.^36,³⁷ People with diabetes should adopt dietary and lifestyle changes to control their glucose levels and other stroke risks as much as possible. (See the Diabetes section.)

Diet: Fruits and Vegetables

Diets high in fruit and/or vegetables are associated with a reduced risk of stroke, according to most studies.^38,³⁹ In a large preliminary study, cruciferous and green leafy vegetables, as well as citrus fruit and juice, conferred the highest degree of protection.⁴⁰ The protective effect of eating produce may result from a variety of components found in these foods, including potassium, magnesium, vitamin E, vitamin C, and beta-carotene, according to most,^41,^42,^43,^44,^45,^46,⁴⁷ but not all research.^48,^49,⁵⁰ Flavonoids found in fruits and vegetables have also been inconsistently linked with decreased stroke risk.^51,⁵² Because it is not clear which components of produce are responsible for the protective effect, people wishing to reduce their risk of stroke should rely primarily on eating more fruits and vegetables themselves rather than on taking supplements.

Diet: Fat Intake

The influence of dietary fat on the risk of stroke is unclear. Some recent reports suggest a link between increased fat intake, including saturated fat (primarily found in meat and dairy), and a decreased stroke risk.^53,⁵⁴ These unexpected findings may be due to unique dietary conditions in one of the countries studied (Japan) or due to flaws in research design.^55,^56,⁵⁷ Other evidence suggests the opposite relationship—that people consuming more saturated fat are at higher risk of stroke.⁵⁸

Evidence regarding the role of unsaturated fats (primarily found in vegetable oils, cooked and processed foods made with vegetable oils, nuts and seeds) is equally unclear,^59,^60,⁶¹ suggesting that unsaturated fats may have different effects on different types of stroke, or that some unsaturated fats differ from others in their influence on stroke risk. Similarly, the benefits of eating fish, which are high in omega-3 fatty acids, remain unknown. Fish consumption has been linked to reduced stroke risk in some,^62,⁶³ but not all^64,⁶⁵ studies.

Diet: Salt Intake

High salt intake is associated with both stroke⁶⁶ and hypertension, a major risk factor for stroke.⁶⁷ Salt intake may increase stroke risk even independent of salt’s effect on blood pressure.⁶⁸ Among overweight persons, an increase in salt consumption of 2.3 grams per day was associated with a 32% increase in stroke incidence and an 89% increase in stroke mortality.⁶⁹ Reducing salt intake is recommended as a way to reduce the risk of stroke.⁷⁰

Diet: Potassium Intake

Researchers have found an association between diets low in potassium and increased risk of stroke.^71,^72,⁷³ People who take potassium supplements have been reported to have a low risk of suffering a stroke.⁷⁴ Others have linked an increased risk of stroke to the combination of low dietary potassium plus high salt intake.⁷⁵

Increasing dietary potassium has lowered blood pressure in humans, which by itself should reduce the risk of stroke;⁷⁶ however, some of the protective effect of potassium appears to extend beyond its ability to lower blood pressure.⁷⁷ Maintaining a high potassium intake is best achieved by eating fruits and vegetables. Avocados, potatoes, watermelon and soybeans are particularly high in potassium.

Estrogen Intake

Early research suggested that women who took estrogen either from birth control pills⁷⁸ or, in some studies, estrogen replacement therapy,⁷⁹ had a higher risk of stroke compared with women not taking these hormones.⁸⁰ Recent studies, however, have found no increase in stroke risk from taking estrogen replacement therapy.^81,⁸² While some newer studies continue to find an association between the risk of stroke and the use of the oral contraceptive,⁸³ most recent reports have not.^84,⁸⁵ Nonetheless, women over 35 years of age who smoke, have high blood pressure, or other risk factors for stroke appear have additional stroke risk from using oral contraceptives, even the low-dose variety.^86,^87,⁸⁸

Exercise

Exercise reduces the risk of stroke according to most^89,^90,^91,^92,⁹³ though not all,^94,^95,^96,^97,⁹⁸ studies. The benefits of exercise are probably due to its effects on body weight, blood pressure, and glucose tolerance. Evidence from a large study, which included subjects from 11 U.S. states, found that simple walking reduced the risk of stroke in middle-aged women.⁹⁹ Brisk or striding walking was associated with an even greater degree of protection than was walking at a casual pace.

Family History

The role of genetics in the development of cerebrovascular disease is unclear. One study found that women, but not men, were at high risk for stroke-related death if they had a family history of the disease.¹⁰⁰ Another study found family history of heart attack, but not stroke, was related to stroke risk in women.¹⁰¹ A third study found family history related to risk only for less common types of stroke.¹⁰² The difficulties in establishing a possible role for genetics in stroke risk may include the existence of different types of strokes with different causes¹⁰³ and the likelihood that many people with stroke risks will die instead of coronary heart disease before a stroke can actually occur.¹⁰⁴

Cardiovascular Disease

Diseases of the blood vessels (atherosclerosis), such as intermittent claudication or coronary heart disease, appear to increase the risk for stroke.^105,^106,¹⁰⁷ With the possible exception of changes in the fat content of the diet, most dietary and lifestyle factors that affect the risk of atherosclerosis-related diseases appear to similarly affect the risk of suffering a stroke.^108,¹⁰⁹ Refer to the Atherosclerosis section for information about prevention.

Homocysteine (High)

Elevated blood levels of homocysteine, an amino acid, have been linked to risk of stroke in most studies.^110,^111,¹¹² What is not clear, however, is whether high homocysteine levels cause strokes or are simply a marker for some other causative factor. Supplementation with folic acid, and vitamins B6 and B12 generally lowers homocysteine levels in humans.^113,^114,¹¹⁵ A preliminary study found low dietary intake of vitamin B6, but not folic acid, was associated with increased stroke risk. However, whether increasing vitamin intake and lowering homocysteine will result in a decrease in the risk of suffering a stroke remains unknown.

Hypertension

Hypertension, or high blood pressure, appears to be the most serious risk factor for stroke, accounting for 70% of all cases.^116,^117,^118,^119,^120,^121,¹²² A systolic blood pressure of over 160 mm Hg increases the risk of stroke approximately 2.5- to 4-fold.¹²³ People with mild to moderate high blood pressure should work with a doctor to lower their blood pressure as much as possible. If dietary and lifestyle changes do not normalize blood pressure, the use of blood pressure-lowering drugs should be considered; blood pressure-lowering medication reduces the risk of stroke risk caused by hypertension.¹²⁴ For more information, see the Hypertension section.

Obesity

Obesity increases the risk for stroke in most studies.^125,¹²⁶ Excess abdominal fat (as opposed to fat accumulation in the thighs and buttocks) appears to be more directly linked to increased risk of stroke.^127,^128,¹²⁹ While losing weight is difficult and keeping it off extremely difficult for most people, normalizing weight with a healthful diet and exercise program is one of the best ways to reduce the risk of many diseases including stroke.

Race

The risk of death from stroke in African-Americans is about twice that in whites,¹³⁰ and has been rising while the risk has been decreasing in non-blacks in the US.¹³¹ The increased risk in African-Americans may be largely due to differences in the incidence of stroke risk factors between blacks and whites—particularly hypertension.¹³² However, much remains unclear about why African-Americans have high rates of stroke, including the relative importance of genetics versus lifestyle factors.¹³³ Hispanics in the Western US have been reported to have less stroke risk than the other racial groups,¹³⁴ though Hispanics in the Eastern US appear to have a greater risk than do whites.¹³⁵ The reason for this discrepancy is unknown.

Smoking

Smoking is associated with a significantly increased risk of stroke.^136,^137,^138,^139,^140,¹⁴¹ Even secondhand smoke puts non-smokers at increased risk.¹⁴² Eliminating exposure to tobacco smoke should be a major health priority for all people.

Transient Ischemic Attack

A transient ischemic attack (TIA) is a temporary paralysis, numbness, speech difficulty or other set of neurologic symptoms that start suddenly and end within 24 hours. People who think they may be having a TIA should seek immediate medical attention.

Those who have suffered a TIA are at high risk for suffering a stroke. As a result, they should also adopt lifestyle and dietary changes to lower their risk, as well as consult their medical doctor for possible drug treatment. People with a history of TIAs who took 400 IU of vitamin E per day with a small amount of aspirin had fewer attacks over the following two years than those who took only aspirin in a double-blind study.¹⁴³

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