Alzheimer's now affects roughly 4.5 million people in the United States,
according to the Alzheimer's Association.
As the U.S. population grows older, the number of people with AD is expected
to increase. But AD is not a normal or inevitable
part of aging. It is a progressive disease that starts in one part of the
brain and gradually invades other regions. As it
progresses, AD destroys nerve cells within the brain and the connections
between them, leaving behind clumps of proteins called
plaques and twisted fibers in brain cells called tangles. Over time, this
destruction erodes the most vital abilities of human
nature: language, learning, memory and reason. Personality and behavior also
are dramatically affected by AD.
Alzheimer's disease is the most common causes of dementia in older people.
Dementia is a medical term used to describe
deterioration in thinking ability severe enough to disrupt a person's normal
activities and relationships. The disease usually begins
in people 65 or older, but in rare instances it can affect individuals as
young as 40. An estimated one in 10 people over 65 have
AD, and close to half of all adults in the United States aged 85 and older
are believed to have at least a mild form of the
disease.
There is no evidence that women are at greater risk than men for developing
the disease. However, nearly 42,000 women die of
AD each year, more than twice the number of men. This is because women live
longer than men so more women have the disease
at any time than men.
Early symptoms of the disease include forgetfulness, difficulty using or
remembering words and difficulty concentrating. For
some individuals, these early symptoms of AD may be mistaken for what many
people consider "natural" symptoms of aging. But
symptoms caused by AD worsen over time, while the short-term memory problems
that trouble many people as they age do not
progress to other more serious symptoms.
The rate that AD symptoms progress varies greatly from person to person. Some
people have AD only for the last three years
of life, while others may live with the disease for 20 years.
Symptoms of Alzheimer's often are divided into three phases: mild, moderate
and severe, though symptoms in these phases
often overlap. Because Alzheimer's damages the brain, unpredictable and
uncharacteristic behavior is common. Anxiety,
aggressiveness or compulsive behaviors—repetitious activities that the person
doesn't seem to be able to control or stop—are
also common. Mood swings and irritability are common and can escalate if not
treated early. These behavioral patterns typically
change as the disease progresses.
The major risk factor for AD is age. According to the Alzheimer's
Association, a person's risk of developing any form of
dementia, including Alzheimer's, doubles approximately every five years after
age 65.
Although researchers still don't know for sure what causes Alzheimer's
disease, most believe it is related to the abnormal
processing of normal brain proteins, particularly amyloid precursor protein
and tau. For some reason, later in life these proteins,
which serve a normal function, begin to be abnormally processed. When this
happens, the abnormally processed proteins
assemble themselves into clumps, which interfere with thinking. These clumped
proteins are called neurofibrillary tangles and
senile (amyloid) plaques (often simply referred to as tangles and plaques),
and eventually destroy critical parts of the brain.
Family history is also a risk factor for AD. For example, early—onset AD, a
rare form of the disease that strikes people
between the ages of 30 and 60, is often inherited. So far, only one genetic
factor has been identified that makes late-stage AD
more likely—a gene that makes a particular form of a protein called
apolipoprotein E (ApoE). Fifteen percent of the population
has this form of ApoE.
Other theories link the disease's development to the death of cells critical
for maintaining levels of certain brain chemicals
required for normal thought processes; chronic inflammation; accumulation of
heavy metals in the brain; and vascular factors that
affect the health of blood vessels in the brain. Another potential risk
factor is severe head injury.
In addition, scientists are investigating the role of education, diet and
environment in AD. They are also looking into the link
between the risk factors of heart disease—such as high blood pressure, high
cholesterol and low levels of folate—and AD. On
the positive side, there is some evidence that higher levels of education
early in life and more social, mental and physical
activities in older age may help prevent the disease.