World Alzheimer's Day, which takes place annually Sept. 21, aims to increase awareness about the most common form of dementia that causes problems with memory, thinking and behavior. Monday marks a day in which "Alzheimer’s organizations around the world concentrate their efforts on raising awareness about Alzheimer’s and dementia," according to the Fisher Center for Alzheimer's Research Foundation.

Below are six facts about World Alzheimer's Day and the disease itself.

1. Millions are affected: The Fisher Center for Alzheimer's Research Foundation says 5.4 million Americans are living with Alzheimer's disease; 47 million people worldwide are living with a form of dementia, according to the Alzheimer's Association.

2. People are diagnosed often: Every 68 seconds someone develops Alzheimer's. With the number of cases growing, some 16 million Americans are predicted to be living with the disease by 2050.

3. Alzheimer's usually occurs in older people: Most people living with Alzheimer's disease are over 65, but those younger than 65 can develop the disease, according to the Centers for Disease Control and Prevention.

4. The disease has proved deadly: Alzheimer's is the sixth-leading cause of death in the United States. People typically live about eight years after their symptoms become noticeable to others, but survival can range from four to 20 years.

5. Go purple: The Alzheimer's Association encourages people to wear purple, the color commonly used to show support for the cause, on World Alzheimer's Day. The organization also suggests supporters of Alzheimer awareness plan events at work or engage on social media to "go purple with a purpose."

6. There are ways to make a difference: A blog post on the Huffington Post lists a few straightforward ways to take action on World Alzheimer's Day, including thanking a caretaker or joining the Alzheimer's Prevention Registry. Check out the full post here.