According to the Alzheimer’s Association, one in three seniors dies with some type of dementia. Alzheimer’s is the most common form of dementia, and is the sixth-leading cause of death in the United States. Both Alzheimer's and dementia remain somewhat mysterious. Doctors don’t fully understand what causes dementia, and people who don’t know someone with dementia may have little understanding of how dementia progresses. Some people mistakenly believe Alzheimer’s is the only type of dementia.