That estimate is based on a new study that found a higher lifetime risk than previously thought: After age 55, people have up to a 4 in 10 chance of eventually developing dementia—if they live long enough.

Dementia cases in the U.S. are expected to double by 2060, with an estimated one million people diagnosed per year, according to a new study led by Johns Hopkins University and other institutions.

A new study found an increased risk of dementia in older Americans, with the risk among Black Americans even greater. NBC News' Anne Thompson reports on what doctors say can help lower the risk of dementia.