By 2060, new dementia cases per year could double to one million because of the growing population of older Americans, a study predicts.

The number of people in the United States who develop dementia each year will double over the next 35 years to about one million annually by 2060, a new study estimates, and the number of new cases per year among Black Americans will triple.

The increase will primarily be due to the growing aging population, as many Americans are living longer than previous generations. By 2060, some of the youngest baby boomers will be in their 90s and many millennials will be in their 70s. Older age is the biggest risk factor for dementia. The study found that the vast majority of dementia risk occurred after age 75, increasing further as people reached age 95.

The study, published Monday in Nature Medicine, found that adults over 55 had a 42 percent lifetime risk of developing dementia. That is considerably higher than previous lifetime risk estimates, a result the authors attributed to updated information about Americans’ health and longevity and the fact that their study population was more diverse than that of previous studies, which have had primarily white participants.

Some experts said the new lifetime risk estimate and projected increase in yearly cases could be overly high, but they agreed that dementia cases would soar in the coming decades.

“Even if the rate is significantly lower than that, we’re still going to have a big increase in the number of people and the family and societal burden of dementia because of just the growth in the number of older people, both in the United States and around the world,” said Dr. Kenneth Langa, a professor of medicine at the University of Michigan, who has researched dementia risk and was not involved in the new study.

Dementia already takes an enormous toll on American families and the country’s health care system. More than six million Americans currently have dementia, nearly 10 percent of people 65 and older, research has found. Experts say that each year in the United States, dementia causes more than 100,000 deaths and accounts for more than $600 billion in caregiving and other costs.

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