The number of people in the United States who develop dementia each year will double over the next 35 years to about 1 million a year by 2060, a new study estimates, and the number of new cases annually among black Americans will triple.
The increase will primarily be the result of an 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 in their 70s. Older age is the biggest risk factor for dementia. The study found that the vast majority of dementia risk occurs after age 75, and increases further as people reach age 95.
The study, published Monday in the journal Nature Medicine, found that adults over the age of 55 have a 42 percent lifetime risk of developing dementia. That’s significantly higher than previous estimates of lifetime risk, a result the authors attributed to updated information about the health and longevity of Americans and the fact that their population was more diverse than that of previous studies, which involved primarily white men.
Some experts said the new lifetime risk estimate and the projected increase in annual cases may be too high, but agreed that dementia cases will rise in the coming decades.
“Even if the rate is significantly lower than that, we will still have a large increase in the number of people and the family and societal burden of dementia just because of the increase 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 researched dementia risk and was not involved in the new study.
Dementia is already taking a huge toll on American families and the nation’s health care system. More than six million Americans currently have dementia, nearly 10 percent of people over age 65, the study 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 care and other costs.
If the new projections are confirmed, there will be about 12 million Americans with dementia in 2060, said Dr. Josef Coresh, director of the Institute for Optimal Aging at New York University’s Grossman School of Medicine and leader of the study, which involved about 100 researchers at 10 universities.
The study underscores the urgency of trying to prevent or slow the onset of dementia, the authors and other experts said. Their main recommendations are to improve people’s cardiovascular health with medication and lifestyle changes; increase efforts to prevent and treat stroke, which can lead to dementia; and encourage people to wear hearing aids, which appear to help prevent dementia by allowing people to be more socially and cognitively engaged.
“You need to see the enormity of the problem,” 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 is huge and not evenly distributed among people,” added Dr. Beiser, noting that the study found a disproportionate risk for black Americans.
Researchers evaluated more than three decades of data from a long-term study of human health in four communities – in Maryland, Mississippi, Minnesota and North Carolina. About 27 percent of the 15,000 participants were black, mostly from Jackson, Miss., said Dr. Coresh. The analysis, 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 blacks will rise to about 180,000 in 2060 from about 60,000 in 2020. The main reason for the tripling of new cases in that population is that the percentage of black Americans living to old age is growing faster than among whites , said dr. Coresh.
In the study, black participants also developed dementia at a younger average age than white participants and had a higher lifetime risk.
“I don’t know if we fully understand it, but at least some of the contributing factors are that vascular risk factors are more common,” said Dr. Coresh, noting that hypertension, diabetes and high cholesterol increase the risk of dementia. He said lower socioeconomic status and education levels among study participants may have also played a role, as could structural racism that affected health.
Predicting dementia risk is complicated for several reasons. The causes of dementia are varied and often not fully understood. The types of dementia also vary and may overlap. The new analysis, like several other studies, did not attempt to estimate how many people will develop Alzheimer’s disease, the most common type of dementia. That’s because many experts believe that aspects of Alzheimer’s disease can overlap with vascular dementia and that both conditions can be triggered by cardiovascular problems, said Dr. Coresh.
Several studies in America and globally have shown that the percentage of dementia cases among older adults has fallen in recent years, most likely due to better treatment of cardiovascular problems and a more educated population, as education can improve brain resilience and overall health.
That reduction is not inconsistent with the new study, experts and authors said, because the study estimated the current level of cumulative dementia risk over people’s lifetimes and projected it forward. It’s possible that positive changes—healthier behaviors and better treatment of conditions like diabetes and stroke, for example—could lower the risk rate at any age in the coming decades, but the number of new cases each year will continue to rise from current numbers. 514,000, due to the growing population of elderly people, experts say.
“Whether it’s a million or 750,000 people a year, there will be a lot of people, and the longer people live, the more dementia there will be,” said Dr. Beiser, who worked on earlier studies of different patients that found lower estimates.
The study also found that women have a higher lifetime risk of dementia than men – 48 percent compared to 35 percent. dr. Coresh said this was primarily because the women in the study lived longer. “Their risk of getting dementia by the time they get to their 95th birthday is higher because more of them will get closer to their 95th birthday,” he said.
dr. Langa said other researchers were trying to find out if there might also be biological differences that increase women’s risk, perhaps “hormonal environments in the body or even potential genetic differences that could affect the female brain in different ways than the male.”
Another high-risk group was people with two copies of the APOE4 gene variant, which greatly increases the risk of Alzheimer’s disease and its development at a younger age than people without the variant. In the study, people with two copies of APOE4 had a lifetime risk of dementia of 59 percent, compared to a lifetime risk of 48 percent for people with one copy and 39 percent for people without the variant.
The analysis used health data from the Atherosclerosis Risk in Communities (known as ARIC) study, which followed people age 55 and older from 1987 to 2020.
The researchers used several methods to determine if and when the participants developed dementia. About a quarter of cases were diagnosed through in-person neuropsychological testing, while the rest were identified through hospital records or death certificates or through telephone assessments. Each method has limitations that could lead to overestimation or underestimation of the actual number of dementia patients, experts say.
The study found that at age 75, the risk of dementia was about 4 percent; at the age of 85 it was 20 percent; and in 1995 it was 42 percent. The researchers applied the percentage risk to population projections from the census to estimate future annual dementia diagnoses.
To reduce the chances of developing dementia, experts and study authors emphasized taking steps to address known risk factors such as diabetes, high blood pressure and hearing loss. A recent Lancet Commission report on dementia lists 14 risk factors that can be improved and concludes that “half the risk of dementia is preventable and it is never too early or too late to address dementia risk,” said Dr. Coresh.
Experts have recommended such steps rather than seeking new Alzheimer’s drugs, which appear to only modestly slow cognitive decline in the early stages of the disease and carry safety risks.
“Because of their relatively limited effectiveness, I don’t think you’re going to get a lot of life-risk-reducing benefit,” said Dr. Langa about new medicines. “I think we’re going to get more bang for the buck from some of these public health and lifestyle interventions that seem to improve overall health and reduce the risk of dementia over time.”
