Who is at Risk for Stroke?
Some people are at a higher risk for stroke than
others. Unmodifiable risk factors include age,
gender, race/ethnicity, and stroke family history.
In contrast, other risk factors for stroke, like
high blood pressure or cigarette smoking, can be
changed or controlled by the person at risk.
Unmodifiable Risk Factors
It is a myth that stroke occurs only in elderly
adults. In actuality, stroke strikes all age groups,
from fetuses still in the womb to centenarians. It
is true, however, that older people have a higher
risk for stroke than the general population and that
the risk for stroke increases with age. For every
decade after the age of 55, the risk of stroke
doubles, and two-thirds of all strokes occur in
people over 65 years old. People over 65 also have a
seven-fold greater risk of dying from stroke than
the general population. And the incidence of
stroke is increasing proportionately with the
increase in the elderly population. When the baby
boomers move into the over-65 age group, stroke and
other diseases will take on even greater
significance in the health care field.
Gender also plays a role in risk for stroke. Men
have a higher risk for stroke, but more women die
from stroke. The stroke risk for men is 1.25 times
that for women. But men do not live as long as
women, so men are usually younger when they have
their strokes and therefore have a higher rate of
survival than women. In other words, even though
women have fewer strokes than men, women are
generally older when they have their strokes and are
more likely to die from them.
Stroke seems to run in some families. Several
factors might contribute to familial stroke risk.
Members of a family might have a genetic tendency
for stroke risk factors, such as an inherited
predisposition for hypertension or diabetes. The
influence of a common lifestyle among family members
could also contribute to familial stroke.
The risk for stroke varies among different ethnic
and racial groups. The incidence of stroke among
African-Americans is almost double that of white
Americans, and twice as many African-Americans who
have a stroke die from the event compared to white
Americans. African-Americans between the ages of 45
and 55 have four to five times the stroke death rate
of whites. After age 55 the stroke mortality rate
for whites increases and is equal to that of African-Americans.
Compared to white Americans, African-Americans
have a higher incidence of stroke risk factors,
including high blood pressure and cigarette smoking.
African-Americans also have a higher incidence and
prevalence of some genetic diseases, such as
diabetes and sickle cell anemia, that predispose
them to stroke.
Hispanics and Native Americans have stroke
incidence and mortality rates more similar to those
of white Americans. In Asian-Americans stroke
incidence and mortality rates are also similar to
those in white Americans, even though Asians in
Japan, China, and other countries of the Far East
have significantly higher stroke incidence and
mortality rates than white Americans. This suggests
that environment and lifestyle factors play a large
role in stroke risk.
The "Stroke Belt"
Several decades ago, scientists and statisticians
noticed that people in the southeastern United
States had the highest stroke mortality rate in the
country. They named this region the stroke belt.
For many years, researchers believed that the
increased risk was due to the higher percentage of
African-Americans and an overall lower socioeconomic
status (SES) in the southern states. A low SES is
associated with an overall lower standard of living,
leading to a lower standard of health care and
therefore an increased risk of stroke. But
researchers now know that the higher percentage of
African-Americans and the overall lower SES in the
southern states does not adequately account for the
higher incidence of, and mortality from, stroke in
those states. This means that other factors must be
contributing to the higher incidence of and
mortality from stroke in this region.
Recent studies have also shown that there is a
stroke buckle in the stroke belt. Three
southeastern states, North Carolina, South Carolina,
and Georgia, have an extremely high stroke mortality
rate, higher than the rate in other stroke belt
states and up to two times the stroke mortality rate
of the United States overall. The increased risk
could be due to geographic or environmental factors
or to regional differences in lifestyle, including
higher rates of cigarette smoking and a regional
preference for salty, high-fat foods.
Other Risk Factors
The most important risk factors for stroke are
hypertension, heart disease, diabetes, and cigarette
smoking. Others include heavy alcohol consumption,
high blood cholesterol levels, illicit drug use, and
genetic or congenital conditions, particularly
vascular abnormalities. People with more than one
risk factor have what is called "amplification of
risk." This means that the multiple risk factors
compound their destructive effects and create an
overall risk greater than the simple cumulative
effect of the individual risk factors.
Hypertension
Of all the risk factors that contribute to stroke,
the most powerful is hypertension, or high blood
pressure. People with hypertension have a risk for
stroke that is four to six times higher than the
risk for those without hypertension. One-third of
the adult U.S. population, about 50 million people
(including 40-70 percent of those over age 65) have
high blood pressure. Forty to 90 percent of stroke
patients have high blood pressure before their
stroke event.
A systolic pressure of 120 mm of Hg over a
diastolic pressure of 80 mm of Hg*
is generally considered normal. Persistently high
blood pressure greater than 140 over 90 leads to the
diagnosis of the disease called hypertension. The
impact of hypertension on the total risk for stroke
decreases with increasing age, therefore factors
other than hypertension play a greater role in the
overall stroke risk in elderly adults. For people
without hypertension, the absolute risk of stroke
increases over time until around the age of 90, when
the absolute risk becomes the same as that for
people with hypertension.
Like stroke, there is a gender difference in the
prevalence of hypertension. In younger people,
hypertension is more common among men than among
women. With increasing age, however, more women than
men have hypertension. This hypertension gender-age
difference probably has an impact on the incidence
and prevalence of stroke in these populations.
Antihypertensive medication can decrease a
person's risk for stroke. Recent studies suggest
that treatment can decrease the stroke incidence
rate by 38 percent and decrease the stroke fatality
rate by 40 percent. Common hypertensive agents
include adrenergic agents, beta-blockers,
angiotensin converting enzyme inhibitors, calcium
channel blockers, diuretics, and vasodilators.
Heart Disease
After hypertension, the second most powerful risk
factor for stroke is heart disease, especially a
condition known as atrial fibrillation.
Atrial fibrillation is irregular beating of the left
atrium, or left upper chamber, of the heart. In
people with atrial fibrillation, the left atrium
beats up to four times faster than the rest of the
heart. This leads to an irregular flow of blood and
the occasional formation of blood clots that can
leave the heart and travel to the brain, causing a
stroke.
Atrial fibrillation, which affects as many as 2.2
million Americans, increases an individual's risk of
stroke by 4 to 6 percent, and about 15 percent of
stroke patients have atrial fibrillation before they
experience a stroke. The condition is more prevalent
in the upper age groups, which means that the
prevalence of atrial fibrillation in the United
States will increase proportionately with the growth
of the elderly population. Unlike hypertension and
other risk factors that have a lesser impact on the
ever-rising absolute risk of stroke that comes with
advancing age, the influence of atrial fibrillation
on total risk for stroke increases powerfully with
age. In people over 80 years old, atrial
fibrillation is the direct cause of one in four
strokes.
Other forms of heart disease that increase stroke
risk include malformations of the heart valves or
the heart muscle. Some valve diseases, like
mitral valve stenosis or mitral annular
calcification, can double the risk for stroke,
independent of other risk factors.
Heart muscle malformations can also increase the
risk for stroke. Patent foramen ovale (PFO)
is a passage or a hole (sometimes called a "shunt")
in the heart wall separating the two atria, or upper
chambers, of the heart. Clots in the blood are
usually filtered out by the lungs, but PFO could
allow emboli or blood clots to bypass the lungs and
go directly through the arteries to the brain,
potentially causing a stroke. Research is currently
under way to determine how important PFO is as a
cause for stroke. Atrial septal aneurysm (ASA), a congenital (present from birth) malformation of the
heart tissue, is a bulging of the septum or heart
wall into one of the atria of the heart. Researchers
do not know why this malformation increases the risk
for stroke. PFO and ASA frequently occur together
and therefore amplify the risk for stroke. Two other
heart malformations that seem to increase the risk
for stroke for unknown reasons are left atrial
enlargement and left ventricular hypertrophy. People
with left atrial enlargement have a larger than
normal left atrium of the heart; those with left
ventricular hypertrophy have a thickening of the
wall of the left ventricle.
Another risk factor for stroke is cardiac surgery
to correct heart malformations or reverse the
effects of heart disease. Strokes occurring in this
situation are usually the result of surgically
dislodged plaques from the aorta that travel through
the bloodstream to the arteries in the neck and
head, causing stroke. Cardiac surgery increases a
person's risk of stroke by about 1 percent. Other
types of surgery can also increase the risk of
stroke.
Blood Cholesterol Levels
Most people know that high cholesterol levels
contribute to heart disease. But many don't realize
that a high cholesterol level also contributes to
stroke risk. Cholesterol, a waxy substance produced
by the liver, is a vital body product. It
contributes to the production of hormones and
vitamin D and is an integral component of cell
membranes. The liver makes enough cholesterol to
fuel the body's needs and this natural production of
cholesterol alone is not a large contributing factor
to atherosclerosis, heart disease, and stroke.
Research has shown that the danger from cholesterol
comes from a dietary intake of foods that contain
high levels of cholesterol. Foods high in saturated
fat and cholesterol, like meats, eggs, and dairy
products, can increase the amount of total
cholesterol in the body to alarming levels,
contributing to the risk of atherosclerosis and
thickening of the arteries.
Cholesterol is classified as a lipid, meaning
that it is fat-soluble rather than water-soluble.
Other lipids include fatty acids, glycerides,
alcohol, waxes, steroids, and fat-soluble vitamins
A, D, and E. Lipids and water, like oil and water,
do not mix. Blood is a water-based liquid, therefore
cholesterol does not mix with blood. In order to
travel through the blood without clumping together,
cholesterol needs to be covered by a layer of
protein. The cholesterol and protein together are
called a lipoprotein.
There are two kinds of cholesterol, commonly
called the "good" and the "bad." Good cholesterol is
high-density lipoprotein, or HDL; bad
cholesterol is low-density lipoprotein, or
LDL. Together, these two forms of cholesterol
make up a person's total serum cholesterol
level. Most cholesterol tests measure the level of
total cholesterol in the blood and don't distinguish
between good and bad cholesterol. For these total
serum cholesterol tests, a level of less than 200
mg/dL** is considered
safe, while a level of more than 240 is considered
dangerous and places a person at risk for heart
disease and stroke.
Most cholesterol in the body is in the form of
LDL. LDLs circulate through the bloodstream, picking
up excess cholesterol and depositing cholesterol
where it is needed (for example, for the production
and maintenance of cell membranes). But when too
much cholesterol starts circulating in the blood,
the body cannot handle the excessive LDLs, which
build up along the inside of the arterial walls. The
buildup of LDL coating on the inside of the artery
walls hardens and turns into arterial plaque,
leading to stenosis and atherosclerosis. This plaque
blocks blood vessels and contributes to the
formation of blood clots. A person's LDL level
should be less than 130 mg/dL to be safe. LDL levels
between 130 and 159 put a person at a slightly
higher risk for atherosclerosis, heart disease, and
stroke. A score over 160 puts a person at great risk
for a heart attack or stroke.
The other form of cholesterol, HDL, is beneficial
and contributes to stroke prevention. HDL carries a
small percentage of the cholesterol in the blood,
but instead of depositing its cholesterol on the
inside of artery walls, HDL returns to the liver to
unload its cholesterol. The liver then eliminates
the excess cholesterol by passing it along to the
kidneys. Currently, any HDL score higher than 35 is
considered desirable. Recent studies have shown that
high levels of HDL are associated with a reduced
risk for heart disease and stroke and that low
levels (less than 35 mg/dL), even in people with
normal levels of LDL, lead to an increased risk for
heart disease and stroke.
A person may lower his risk for atherosclerosis
and stroke by improving his cholesterol levels. A
healthy diet and regular exercise are the best ways
to lower total cholesterol levels. In some cases,
physicians may prescribe cholesterol-lowering
medication, and recent studies have shown that the
newest types of these drugs, called reductase
inhibitors or statin drugs, significantly reduce the
risk for stroke in most patients with high
cholesterol. Scientists believe that statins may
work by reducing the amount of bad cholesterol the
body produces and by reducing the body's
inflammatory immune reaction to cholesterol plaque
associated with atherosclerosis and stroke.
*mm
of Hg-or millimeters of mercury-is the standard
means of expressing blood pressure, which is
measured using an instrument called a
sphygmomanometer. Using a stethoscope and a cuff
that is wrapped around the patient's upper arm, a
health professional listens to the sounds of blood
rushing through an artery. The first sound
registered on the instrument gauge (which measures
the pressure of the blood in millimeters on a column
of mercury) is called the systolic pressure. This is
the maximum pressure produced as the left ventricle
of the heart contracts and the blood begins to flow
through the artery. The second sound is the
diastolic pressure and is the lowest pressure in the
artery when the left ventricle is relaxing.
return to "Hypertension"
section
**mg/dL
describes the weight of cholesterol in milligrams in
a deciliter of blood. This is the standard way of
measuring blood cholesterol levels.
Diabetes
Diabetes is another disease that increases a
person's risk for stroke. People with diabetes have
three times the risk of stroke compared to people
without diabetes. The relative risk of stroke from
diabetes is highest in the fifth and sixth decades
of life and decreases after that. Like hypertension,
the relative risk of stroke from diabetes is highest
for men at an earlier age and highest for women at
an older age. People with diabetes may also have
other contributing risk factors that can amplify the
overall risk for stroke. For example, the prevalence
of hypertension is 40 percent higher in the diabetic
population compared to the general population.
Modifiable Lifestyle Risk Factors
Cigarette smoking is the most powerful modifiable
stroke risk factor. Smoking almost doubles a
person's risk for ischemic stroke, independent of
other risk factors, and it increases a person's risk
for subarachnoid hemorrhage by up to 3.5 percent.
Smoking is directly responsible for a greater
percentage of the total number of strokes in young
adults than in older adults. Risk factors other than
smoking - like hypertension, heart disease, and
diabetes - account for more of the total number of
strokes in older adults.
Heavy smokers are at greater risk for stroke than
light smokers. The relative risk of stroke decreases
immediately after quitting smoking, with a major
reduction of risk seen after 2 to 4 years.
Unfortunately, it may take several decades for a
former smoker's risk to drop to the level of someone
who never smoked.
Smoking increases the risk of stroke by promoting
atherosclerosis and increasing the levels of blood-clotting
factors, such as fibrinogen. In addition to
promoting conditions linked to stroke, smoking also
increases the damage that results from stroke by
weakening the endothelial wall of the
cerebrovascular system. This leads to greater damage
to the brain from events that occur in the secondary
stage of stroke. (The secondary effects of stroke
are discussed in greater detail in the
Appendix.)
High alcohol consumption is another modifiable
risk factor for stroke. Generally, an increase in
alcohol consumption leads to an increase in blood
pressure. While scientists agree that heavy drinking
is a risk for both hemorrhagic and ischemic stroke,
in several research studies daily consumption of
smaller amounts of alcohol has been found to provide
a protective influence against ischemic stroke,
perhaps because alcohol decreases the clotting
ability of platelets in the blood. Moderate
alcohol consumption may act in the same way as
aspirin to decrease blood clotting and prevent
ischemic stroke. Heavy alcohol consumption, though,
may seriously deplete platelet numbers and
compromise blood clotting and blood viscosity,
leading to hemorrhage. In addition, heavy drinking
or binge drinking can lead to a rebound effect after
the alcohol is purged from the body. The
consequences of this rebound effect are that blood
viscosity (thickness) and platelet levels skyrocket
after heavy drinking, increasing the risk for
ischemic stroke.
The use of illicit drugs, such as cocaine and
crack cocaine, can cause stroke. Cocaine may act on
other risk factors, such as hypertension, heart
disease, and vascular disease, to trigger a stroke.
It decreases relative cerebrovascular blood flow by
up to 30 percent, causes vascular constriction, and
inhibits vascular relaxation, leading to narrowing
of the arteries. Cocaine also affects the heart,
causing arrhythmias and rapid heart rate that can
lead to the formation of blood clots.
Marijuana smoking may also be a risk factor for
stroke. Marijuana decreases blood pressure and may
interact with other risk factors, such as
hypertension and cigarette smoking, to cause rapidly
fluctuating blood pressure levels, damaging blood
vessels.
Other drugs of abuse, such as amphetamines,
heroin, and anabolic steroids (and even some common,
legal drugs, such as caffeine and L-asparaginase and
pseudoephedrine found in over-the-counter
decongestants), have been suspected of increasing
stroke risk. Many of these drugs are
vasoconstrictors, meaning that they cause blood
vessels to constrict and blood pressure to rise.
Head and Neck Injuries
Injuries to the head or neck may damage the
cerebrovascular system and cause a small number of
strokes. Head injury or traumatic brain injury may
cause bleeding within the brain leading to damage
akin to that caused by a hemorrhagic stroke. Neck
injury, when associated with spontaneous tearing of
the vertebral or carotid arteries caused by sudden
and severe extension of the neck, neck rotation, or
pressure on the artery, is a contributing cause of
stroke, especially in young adults. This type of
stroke is often called "beauty-parlor syndrome,"
which refers to the practice of extending the neck
backwards over a sink for hair-washing in beauty
parlors. Neck calisthenics, "bottoms-up" drinking,
and improperly performed chiropractic manipulation
of the neck can also put strain on the vertebral and
carotid arteries, possibly leading to ischemic
stroke.
Infections
Recent viral and bacterial infections may act with
other risk factors to add a small risk for stroke.
The immune system responds to infection by
increasing inflammation and increasing the infection-fighting
properties of the blood. Unfortunately, this immune
response increases the number of clotting factors in
the blood, leading to an increased risk of embolic-ischemic
stroke.
Genetic Risk Factors
Although there may not be a single genetic factor
associated with stroke, genes do play a large role
in the expression of stroke risk factors such as
hypertension, heart disease, diabetes, and vascular
malformations. It is also possible that an increased
risk for stroke within a family is due to
environmental factors, such as a common sedentary
lifestyle or poor eating habits, rather than
hereditary factors.
Vascular malformations that cause stroke may have
the strongest genetic link of all stroke risk
factors. A vascular malformation is an abnormally
formed blood vessel or group of blood vessels. One
genetic vascular disease called CADASIL, which
stands for cerebral autosomal dominant arteriopathy
with subcortical infarcts and leukoencephalopathy.
CADASIL is a rare, genetically inherited, congenital
vascular disease of the brain that causes strokes,
subcortical dementia, migraine-like headaches, and
psychiatric disturbances. CADASIL is very
debilitating and symptoms usually surface around the
age of 45. Although CADASIL can be treated with
surgery to repair the defective blood vessels,
patients often die by the age of 65. The exact
incidence of CADASIL in the United States is unknown.
¿Do you need more information on
Stroke?
|
"Stroke: Hope Through Research," NINDS.
Publication date
July 2004.
NIH Publication No. 99-2222
|
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