The number of people in the United States who develop dementia each year will double over the next 35 years to about 1 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 older than 55 had a 42% 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 6 million Americans currently have dementia, nearly 10% 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.

If the new projections are borne out, there will be about 12 million Americans with dementia in 2060, said Dr. Josef Coresh, director of the Optimal Aging Institute at New York University’s Grossman School of Medicine and a leader of the study, which involved about 100 researchers at 10 universities.

The study reinforces the urgency of trying to prevent or slow the onset of dementia, the authors and other experts said. Their major recommendations are to improve people’s cardiovascular health with medication and lifestyle changes; increase efforts to prevent and treat strokes, which can lead to dementia; and encourage people to wear hearing aids, which appear to help forestall dementia by allowing people to be more social and cognitively engaged.

“One needs to see the huge magnitude of the issue,” said Alexa Beiser, a professor of biostatistics at Boston University School of Public Health, who was not involved in the new study but evaluated it as an independent reviewer for the journal. “It’s enormous, and it’s not equally distributed among people,” Beiser added, noting that the study found disproportionate risk for Black Americans.

The researchers evaluated more than three decades of data from a long-running study of the health of people in four communities — in Maryland, Mississippi, Minnesota and North Carolina. About 27% of the 15,000 participants were Black, Coresh said. The analysis, which was funded by the National Institutes of Health, focused on Black and white participants because there were not many participants from other racial and ethnic groups, the authors said.

The study estimated that the number of new annual cases among Black people would surge to about 180,000 in 2060 from about 60,000 in 2020. The main reason is that the percentage of Black Americans living to the oldest ages is growing faster than among white people.