What Is Alzheimer’s Disease? Symptoms and Causes

Medically reviewed by
Evelyn O. Berman, MD
, Assistant Professor of Neurology and Pediatrics at University of Rochester, Rochester, NY  | Written by 
Kent Stoneking

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Alzheimer’s disease is a disease affecting the brain. It damages the brain over time in a way that lowers the ability to think and remember things. As the disease gets worse, even the simplest tasks cannot be done. More than 6 million people over the age of 65 years in America may have Alzheimer’s disease. People under 65 years of age may also have Alzheimer’s disease, but the number is not known for sure.1

In 1906, Dr. Alois Alzheimer, for whom the disease was named, examined the brain of a patient that died who had unusual symptoms of mental illness. The symptoms included memory loss, difficulty with language, and behavior patterns that were unpredictable.1 Many abnormal clumps of protein (plaques) and tangled nerve fiber bundles (neurofibrillary tangles) were found in the brain.

Another common feature of the disease is the loss of connections between nerve cells (neurons) in the brain.1 These connections carry messages between different parts of the brain, and from the brain to other parts of the body. The brain has around 100 billion neurons.2 Neurons are responsible for thinking, learning, and remembering as well as senses and muscle movements.

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What Causes Alzheimer’s Disease?

The exact cause of Alzheimer’s disease is still unknown.3 Researchers are focusing on how the abnormal proteins and tangles might cause Alzheimer’s disease. The plaques of abnormal clumps are made of a protein called beta-amyloid. It is likely that plaques have damaging effects on nerve cells and that they upset communication between them. The tangled nerve fiber bundles are caused by another protein called tau. These tangles alter the carrying of nutrients, which results in damage to the nerve cells.

Most scientists think that Alzheimer’s disease is most likely caused by lifestyle and environmental factors. These factors affect the brain over many years.3 Genetics is also thought to be a factor in some cases but may cause less than 1% of cases overall. Having a parent or sibling with Alzheimer’s disease might slightly increase the risk. Alzheimer’s disease usually starts later in life, but when genetic factors are involved it usually develops in middle age.

Risk Factors for Alzheimer’s Disease

Getting older is the biggest risk factor for developing Alzheimer’s disease.3 Patients older than 65 years are at the highest risk for developing Alzheimer’s disease, and the risk of developing the disease increases as people continue to age. More women, because they live longer than men, will develop Alzheimer’s disease.

A number of other factors are associated with developing Alzheimer’s disease, including:3

  • Down syndrome
  • Mild cognitive impairment with memory loss as the primary symptom
  • Head injury, especially in people over 50 years of age with multiple traumatic brain injuries
  • Exposure to air pollution, such as automobile exhaust and wood smoke
  • Certain lifestyle factors, such as poor sleep, lack of exercise, obesity, smoking (including secondhand smoke), high blood pressure, high cholesterol, and type 2 diabetes that is poorly controlled.

Early Signs and Symptoms of Alzheimer’s

The term for loss of memory and other thinking abilities that also have an impact on daily life is dementia. Of the various causes of dementia, Alzheimer’s disease is the most common.2 It is estimated that Alzheimer’s disease is responsible for 60 to 80% of all dementia cases.

The early signs of Alzheimer’s disease usually involve memory. Damage to the brain caused by Alzheimer’s disease can start many years before symptoms are noticed. The part of the brain that is involved in memory is often damaged first.3 Nerve cells are damaged and die in a pattern that is somewhat predictable. Eventually, other parts of the brain are affected. In late-stage Alzheimer’s disease, significant shrinkage of brain tissue is common.

The most common early symptom of Alzheimer’s disease is difficulty remembering recent information, such as a conversation or an event.2 Most people, as they age, notice some slowness in thinking and difficulty recalling things from time to time. However, when there is serious memory loss, confusion, or major changes in thinking patterns, this may be a sign that brain cells are failing. A decline in other aspects of thinking may be noticed, such as finding the right words, difficulty recognizing faces or finding objects, and poor decision-making.1 Basic activities of daily life may also become difficult.

Diagnosis and Testing for Alzheimer’s

The symptoms that a person describes to their doctor, as well as the viewpoint of close family members or friends, are key components to the diagnosis of Alzheimer’s disease.4 Signs of dementia are usually more easily observed by family members and friends than they are for the people who display them. How these symptoms affect the person’s daily life is another important consideration. To confirm their diagnosis, the doctor will do tests that compare the person’s memory and thinking skills with those skills in people of a similar age and education (called neuropsychological tests).

Diagnosis of Alzheimer’s disease also involves an assessment of the person’s neurological and physical health.4 Neurological tests involve the nerves and muscles (reflexes, muscle strength, and tone), balance and coordination (ability to rise from a chair and walk across the room), and the senses (sight and hearing).

To clarify if there are other possible causes for dementia besides Alzheimer’s disease, laboratory tests can be done.4 A thyroid disorder or vitamin deficiency that may lead to memory problems or confusion can be detected by blood tests. Levels of amyloid and tau proteins can be measured in the spinal fluid.

Brain imaging can help the doctor see abnormalities in the structure of the brain, so it can be used to identify medical conditions besides Alzheimer’s disease.4 Methods of brain imaging include magnetic resonance imaging (MRI) and computerized tomography (CT). An MRI uses radio waves and a strong magnetic field to produce detailed pictures of the brain and is the preferred method of diagnosing dementia. A CT scan produces cross-sectional images of the brain and can be used to identify tumors, strokes, or head injuries.

Imaging using positron emission tomography (PET) is another useful diagnostic tool.4 In a PET scan, a low-level radioactive drug, or tracer, is injected into the blood to show a particular feature in the brain. Fluorodeoxyglucose (FDG) PET scans show areas of the brain that have low cellular activity, helping to distinguish between Alzheimer’s disease and other types of dementia. Amyloid PET and tau PET imaging are used primarily in research settings, although they may be used to help diagnose unusual cases of dementia. Amyloid PET imaging measures amyloid deposits in the brain and may be used in people with unusual or early onset dementia symptoms. Tau PET imaging measures the effect of neurofibrillary tangles on brain function.

Stages of Alzheimer’s Disease

Even simple, everyday activities can pose difficulties for people with Alzheimer’s disease. Driving a car, cooking a meal, or paying bills can become a challenge.1 The loss of memory and thinking skills may result in them repeatedly asking the same questions, getting lost easily, losing items in strange places, and being confused by the simplest things. Symptoms increase in severity as Alzheimer’s disease spreads through the brain. These can include disorientation, changes in mood and behavior, deepening confusion about events, time, and place, and unfounded suspicions about people close to them.2

Changes caused by Alzheimer’s disease such as memory and language loss and impaired judgment might make it difficult to treat other health conditions.3 Difficulties in communication in people with Alzheimer’s disease may prevent them from saying that they are feeling pain, explaining symptoms of another illness, following a prescribed treatment plan, or explaining medication side effects.

Brain changes from Alzheimer’s disease progression result in changes to physical function. In its last stages, swallowing, balance, and bowel and bladder control may be affected.3 These effects can increase the likelihood of having additional health problems such as inhaling food or liquid into the lungs, infections such as flu and pneumonia, falls, fractures, bedsores, poor nutrition or dehydration, constipation or diarrhea, and dental problems such as mouth sores or tooth decay.

Other Alzheimer’s Disease FAQs

Is Alzheimer’s disease hereditary?

Though genetics appear to play a factor in whether someone may develop Alzheimer’s disease, Alzheimer’s is rarely (in fewer than 1% of cases) caused by a specific genetic change rather than a confluence of factors.3 Alzheimer’s that is caused by a specific gene mutation is more closely linked to early-onset Alzheimer’s, which is much rarer than late-onset Alzheimer’s. A child of someone with early onset Alzheimer’s is more likely to develop Alzheimer’s as well but is not certain to do so.5

Is Alzheimer’s disease curable?

There is no cure for Alzheimer’s disease.5 However, there are some treatments that help manage symptoms of Alzheimer’s. Researchers are also working on experimental interventions such as new drugs in clinical trials with Alzheimer’s participants.

Can Alzheimer’s disease be prevented?

No, there is no surefire way of preventing Alzheimer’s disease based on what we know today.5 However, scientists are exploring the role of healthy lifestyle choices in slowing down, delaying, or even preventing Alzheimer’s disease. Such lifestyle choices include physical factors such as good nutrition, regular exercise, and controlling weight and blood pressure, as well as environmental and behavioral factors such as social ties and intellectual exercise.

Where can I find financial help for people with Alzheimer’s disease or their caregivers?

Depending on a person’s circumstances, there are several programs offered by federal and state government agencies that can help with healthcare-related costs.5 The National Institute on Aging has information on their website. The following organizations also offer help with finding financial help:

Resources for Alzheimer’s Disease

If you or someone you know has been diagnosed with Alzheimer’s disease or another dementia, you are not alone.2 The Alzheimer’s Association is the trusted resource for reliable information, education, referral, and support to millions of people affected by the disease.

Call the Alzheimer’s Association 24/7 Helpline

Other Helpful Resources Include1