Alzheimer’s disease is a brain disease that slowly destroys memory and thinking skills and, eventually, the ability to carry out the simplest tasks. It begins slowly and gets worse over time. Currently, it has no cure.

Alzheimer’s disease is the most common cause of dementia among older people. Dementia is a loss of thinking, remembering, and reasoning skills that interferes with a person’s daily life and activities. Dementia ranges in severity from the mild stage, when it is just beginning to affect a person’s functioning, to the severe stage, when the person must depend completely on others for basic care.

Estimates vary, but experts suggest that more than 5 million Americans may have Alzheimer's disease. Alzheimer’s is currently ranked as the sixth leading cause of death in the United States, but recent estimates indicate that the disorder may rank third, just behind heart disease and cancer, as a cause of death for older people

In most people with Alzheimer’s, symptoms first appear in their mid-60s, and the risk of developing the disease increases with age. While younger people -- in their 30s, 40s, and 50s -- may get Alzheimer's disease, it is much less common. It is important to note that Alzheimer's disease is not a normal part of aging. 

The course of Alzheimer’s disease—which symptoms appear and how quickly changes occur—varies from person to person. The time from diagnosis to death varies, too. It can be as little as 3 or 4 years if the person is over 80 years old when diagnosed or as long as 10 years or more if the person is younger. 

Memory problems are typically one of the first signs of Alzheimer’s disease, though initial symptoms may vary from person to person. A decline in other aspects of thinking, such as finding the right words, vision/spatial issues, and impaired reasoning or judgment, may also signal the very early stages of Alzheimer’s disease. 

People with Alzheimer’s have trouble doing everyday things like driving a car, cooking a meal, or paying bills. They may ask the same questions over and over, get lost easily, lose things or put them in odd places, and find even simple things confusing. Some people become worried, angry, or violent. 

Not all people with memory problems have Alzheimer’s disease. Mild forgetfulness can be a normal part of aging. Some people may notice that it takes longer to learn new things, remember certain words, or find their glasses. That’s different from a serious memory problem, which makes it hard to do everyday things.

Sometimes memory problems are related to health issues that are treatable. For example, medication side effects, vitamin B12 deficiency, head injuries, or liver or kidney disorders can lead to memory loss or possibly dementia. Emotional problems, such as stress, anxiety, or depression, can also make a person more forgetful and may be mistaken for dementia. 

Some older people with memory or other thinking problems have a condition called mild cognitive impairment, or MCI. MCI can be an early sign of Alzheimer’s, but not everyone with MCI will develop Alzheimer’s disease. People with MCI have more memory problems than other people their age, but they can still take care of themselves and do their normal activities.

Signs of MCI may include

If you or someone in your family thinks your forgetfulness is getting in the way of your normal routine, it’s time to see your doctor. Seeing the doctor when you first start having memory problems can help you find out what’s causing your forgetfulness.

Alzheimer's disease 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. After she died, he examined her brain and found many abnormal clumps (now called amyloid plaques) and tangled bundles of fibers (now called neurofibrillary, or tau, tangles). Plaques and tangles in the brain are two of the main features of Alzheimer's disease. Another is the loss of connections between nerve cells (neurons) in the brain. Neurons send messages between different parts of the brain, and from the brain to muscles and organs in the body.

It seems likely that damage to the brain starts 10 years or more before memory or other thinking problems become obvious. During the earliest stage of Alzheimer’s, people are free of symptoms, but harmful changes are taking place in the brain. The damage at first appears to take place in cells of the hippocampus, the part of the brain essential in forming memories. Abnormal protein deposits form plaques and tangles in the brain. Once-healthy nerve cells stop functioning, lose connections with each other, and die. As more nerve cells die, other parts of the brain begin to shrink. By the final stage of Alzheimer’s, damage is widespread, and brain tissue has shrunk significantly.