Alzheimer’s disease (AD) is the most common cause of dementia in older people. A dementia is a medical condition that disrupts the way the brain works. AD affects the parts of the brain that control thought, memory, and language. Every day, scientists learn more about AD, but right now the cause of the disease still is unknown, and there is no cure. An estimated 4 million people in the United States suffer from AD.
The disease usually begins after age 65, and risk of AD goes up with age. While younger people also may have AD, it is much less common. About 3 percent of men and women ages 65 to 74 have AD, and nearly half of those age 85 and older may have the disease. It is important to note, however, that AD is not a normal part of aging.
AD is named after Dr. Alois Alzheimer, a German doctor. In 1906, Dr. Alzheimer noticed changes in the brain tissue of a woman who had died of an unusual mental illness. He found abnormal clumps (now called senile or neuritic plaques) and tangled bundles of fibers (now called neurofibrillary tangles). Today, these plaques and tangles in the brain are considered hallmarks of AD.
Scientists also have found other changes in the brains of people with AD. There is a loss of nerve cells in areas of the brain that are vital to memory and other mental abilities. There also are lower levels of chemicals in the brain that carry complex messages back and forth between billions of nerve cells. AD may disrupt normal thinking and memory by blocking these messages between nerve cells.
U.S Department of Health and Human Services
Public Health Service
National Institutes of Health
National Institute on Aging