Dementia is a much-feared prospect of getting older, but it's increasingly common: Experts estimate that the number of Americans with dementia will double by the year 2040, as a growing population ages and people live longer. Although the condition is progressive, it's important to recognize dementia early and seek treatment so its advancement can be slowed. These are some of the most common symptoms of dementia; forgetting one thing, in particular, is a red flag for the condition. To find out