What are the causes and risk factors for Alzheimer's disease?

One leading theory for the cause of Alzheimer's disease involves the impairment of clearance from the brain of a sticky material called amyloid. When amyloid is not cleared away properly, the amyloid forms clumps that are poisonous to brain cells. Most experimental therapies in trials today are aimed at slowing amyloid accumulation or hastening amyloid breakdown.

Tangles and plaques of amyloid protein in the brain were once thought to be the defining characteristic of Alzheimer's disease. Studies indicate that dementia in Alzheimer's patients stems from the shrinkage and death of neurons, or nerve cells, and loss of synapses, the connections between nerve cells, not from the tangles and plaques themselves. According to the leading hypothesis, small fragments of amyloid protein may be the toxic factor, triggering a cascade of biochemical events leading to cell death.

Neurons and synapses are continually lost. Levels of neurotransmitters, chemicals that carry complex messages back and forth among billions of nerve cells, are also diminished. In advanced Alzheimer's disease, the dramatic loss of neurons causes the brain to shrink.

To date, we don’t know exactly what causes Alzheimer’s. While increasing age is the most common risk factor, Alzheimer's is not a normal part of aging. In early-onset Alzheimer’s, genetics appear to play a role. Scientists have identified several rare genes that are believed to trigger the disease, and people who inherit these genes are more likely to show symptoms of Alzheimer’s in their 40s and 50s. This genetically influenced form is known as “familial Alzheimer's disease” and tends to affect family members over several generations.

The causes of Alzheimer's disease are mysterious, but much has been learned about how it develops and its consequences.

Alzheimer's affects a person's memory, thought processes and language ability.

As the disease progresses, even rudimentary actions such as swallowing can become impaired or, sometimes even impossible.

Alzheimer's shrinks the brain and destroys some of the brain's 100 billion neurons.

It was named after Dr. Alois Alzheimer, who in 1906 discovered unexpected changes in the brain matter of a deceased patient, who before her death had exhibited many of the now recognized symptoms of Alzheimer's disease.

There are several theories about the scientific cause of Alzheimer's disease. Studies have shown that Alzheimer's patients have deterioration of brain tissue characterized by tangled neurons, brain plaques and defects in neurotransmitter production. This has been thought to be caused by abnormal protein overproduction (amyloid or tau) that can be caused by abnormal genes. It has been proposed but not proved that in addition to defective genes, environmental factors such as a history of head injury, smoking, midlife obesity and a diet high in saturated fats may increase the chances of acquiring Alzheimer's.

Dr. Neal D. Barnard, MD
Psychiatrist (Therapist)

Alzheimer's disease is caused by the build up of amyloid plaques and tangles in the brain, which work together to destroy the brain cells. In this video, Neal Barnard, MD, gives a detailed explanation of the causes of Alzheimer's disease.

No one knows what causes Alzheimer's disease but genetics are believed to play a role as roughly 5 and 15 percent of all cases develop within families. The main risk factor for Alzheimer's disease is increased age. Other risk factors include high blood pressure, coronary artery disease, and diabetes. However, the specifics are still unclear.

Continue Learning about Alzheimer's Disease Causes

Type 3 Diabetes: The Alzheimer’s-Glucose Connection
Type 3 Diabetes: The Alzheimer’s-Glucose Connection
Alzheimer’s disease is common and mysterious, well-documented and hidden. Though it affects an estimated 5.4 million Americans (5.3 million are 65 or ...
Read More
Are low levels of DHA a risk factor for Alzheimer’s disease?
Dr. Mehmet Oz, MDDr. Mehmet Oz, MD
Low levels of docosahexaenoic acid, or DHA may be a risk factor for Alzheimer’s disease and possibly...
More Answers
Who is affected by Alzheimer's disease?
John H. Growdon, MDJohn H. Growdon, MD
The risk of Alzheimer's rises steadily with age. One in eight people ages 65 and older is affect...
More Answers
Are Down Syndrome Therapies Similar to Alzehimer's Disease Therapies?
Are Down Syndrome Therapies Similar to Alzehimer's Disease Therapies?

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.