Alzheimer's disease is a brain disorder that gets worse over time. It's characterized by changes in the brain that lead to deposits of certain proteins. Alzheimer's disease causes the brain to shrink and brain cells to eventually die. Alzheimer's disease is the most common cause of dementia — a gradual decline in memory, thinking, behavior and social skills. These changes affect a person's ability to function.

About 6.5 million people in the United States age 65 and older live with Alzheimer's disease. Among them, more than 70% are 75 years old and older. Of the about 55 million people worldwide with dementia, 60% to 70% are estimated to have Alzheimer's disease.

The early signs of the disease include forgetting recent events or conversations. Over time, it progresses to serious memory problems and loss of the ability to perform everyday tasks.

Medicines may improve or slow the progression of symptoms. Programs and services can help support people with the disease and their caregivers.

There is no treatment that cures Alzheimer's disease. In advanced stages, severe loss of brain function can cause dehydration, malnutrition or infection. These complications can result in death.

Memory loss is the key symptom of Alzheimer's disease. Early signs include difficulty remembering recent events or conversations. But memory gets worse and other symptoms develop as the disease progresses.

At first, someone with the disease may be aware of having trouble remembering things and thinking clearly. As symptoms get worse, a family member or friend may be more likely to notice the issues.

Everyone has memory lapses at times, but the memory loss associated with Alzheimer's disease persists and gets worse. Over time, memory loss affects the ability to function at work or at home.

People with Alzheimer's disease may:

• Repeat statements and questions over and over.
• Forget conversations, appointments or events.
• Misplace items, often putting them in places that don't make sense.
• Get lost in places they used to know well.
• Eventually forget the names of family members and everyday objects.
• Have trouble finding the right words for objects, expressing thoughts or taking part in conversations.
• Alzheimer's disease causes difficulty concentrating and thinking, especially about abstract concepts such as 

  numbers. Doing more than one task at once is especially difficult. It may be challenging to manage finances, balance checkbooks and pay bills on time. 

  Eventually, a person with Alzheimer's disease may be unable to recognize and deal with numbers. 

A number of conditions can result in memory loss or other dementia symptoms. Some of those conditions can be treated. If you are concerned about your memory or other thinking skills, talk to your health care provider.

If you are concerned about thinking skills you observe in a family member or friend, talk about your concerns and ask about going together to talk to a provider.