Dementia of Alzheimer's kind is the most common. It is an advancing disease starting with mild memory loss and possibly leading to loss of the ability to carry on a conversation and respond to the environment. Alzheimer's disease includes parts of the brain that control thought, memory, and language.In the United States, 6.5 million adults 65 and older have 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 approximated to have Alzheimer's disease.