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Alzheimer’s disease and other related dementias are characterized by progressive cognitive decline, and with an aging population, the number of older Americans with dementia is expected to rise dramatically in coming years. But dementia is not an inevitable part of aging.

New studies funded by the National Institute on Aging (NIA) identify early warning signs of cognitive decline and key factors that contribute to dementia risk. Early diagnosis allows access to treatments that can delay the onset or slow the development of dementia, improving the health and well-being of dementia patients and their caregivers and reducing health care costs.

Brain Scans Can Help Predict Future Risk

Identifying who is likely to develop cognitive decline and dementia—and when—is key to early intervention.

By combining brain scan analysis with clinical measures (such as hearing and memory issues),  Phoebe Imms, Andrei Irimia, and colleagues at the University of Southern California (USC) predicted future cognitive decline in cognitively normal older adults with 81% to 91% accuracy.¹ The closer the person was to developing cognitive decline over a 15-year period, the more accurate the prediction.

For the study, the research team used a USC-developed AI model that analyzed magnetic resonance imaging (MRI) scans, measuring multiple subtle features of brain aging that can be difficult to detect.

A wide body of research considers brain aging as a reliable biomarker for the risk of neurodegenerative diseases, such as Alzheimer’s. Risk increases when a person’s brain exhibits features that look older than expected for their age. Using USC’s AI model to analyze the scans, the researchers were able to detect brain anatomy markers associated with cognitive decline.

Various clinical, health, and demographic risk factors can help identify about seven in 10 older adults who will later develop cognitive impairment, the researchers report; adding evidence of brain aging increases the accuracy of predictions.

The researchers studied the brain scans and health indicators of 600 older adults, roughly half of whom later developed cognitive impairment. Along with evidence of brain aging, factors in neurologically healthy older adults that they linked to future cognitive impairment included the APOE genotype, certain cognitive test scores, hearing impairment, self-reported memory impairment, and depression symptoms.

Their findings suggest that adults less than 2.5 years away from experiencing cognitive impairment may be nearing “a critical point of no return along their structural brain trajectories toward Alzheimer’s disease,” the researchers report.

“If we know who is at the greatest risk of developing Alzheimer’s disease in three to five years or more, then their health care providers can intervene early to reduce the duration of ill-health by promoting lifestyle changes, addressing modifiable risk factors such as providing hearing aids, and encouraging family support,” said Imms, pointing to a new comprehensive Lancet report on dementia prevention and intervention.

Ongoing, Unintended Weight Loss May Signal Future Diagnosis

Weight loss begins at least 10 years before a dementia diagnosis, accelerates about two to four years immediately before the onset of symptoms, and continues after diagnosis, a new study documents.²

Continuous weight loss is as a “vital warning sign for dementia progression,” conclude Yuan S. Zhang of Columbia University and Virginia W. Chang of New York University, who conducted their study in part with NIA support via the Carolina Center for Population Aging and Health.

The researchers used 16 years of data (2000 to 2016) from the nationally representative Health and Retirement Study, which assesses older adults’ physical and cognitive health every two years. By examining weight changes years before diagnosis, they illuminate the challenges in examining obesity alone as a risk factor for dementia.

The extent of a person’s weight loss as dementia evolves appears related to their initial body mass index (BMI), Zhang and Chang report. Those with obesity at baseline (BMI ≥ 30) experienced much greater BMI decline than those in the normal weight category (BMI 18.5 to 24.9), underscoring the importance of weight monitoring in all older adults (see figure). Women also experienced a larger BMI decline than men before a dementia diagnosis.

Figure. Weight Loss Begins at Least 10 Years Before a Dementia Diagnosis, and Is Greater for Women and People With Obesity

BMI Changes Among Men Ages 50+ Before and After Dementia Diagnosis, by Baseline BMI

BMI Changes Among Women Ages 50+ Before and After Dementia Diagnosis, by Baseline BMI

Source: Yuan S. Zhang and Virginia W. Chang, “Time Path of Weight Status Before and After Incident Dementia,” Journal of Aging and Health 36, no. 1–2 (2024): 98–109.

Various behavior and physical changes tied to dementia development can cause weight loss due to loss of appetite, pain, and/or high energy expenditure caused by increased physical activity (such as excessive pacing) or higher energy needs, the researchers note. Also, metabolic and hormonal changes related to weight loss may accelerate the dementia process.

Recognizing the early signs of dementia development “can help promote early diagnosis and subsequent access to services, support, and interventions, which can be crucial for delaying institutionalization, maintaining quality of life, improving the health and well-being of caregivers and family, and reducing the cost of long-term care for the health care system,” they wrote.

Serious Infections Raise Risk for Decades

Individuals hospitalized with an infection were three times more likely to be diagnosed with dementia over the next 30 years than those not hospitalized with an infection, reports a team of researchers from the University of Michigan, Duke University, and the University of Auckland.³

Hospitalization for serious viral, bacterial, parasitic, and other infections was linked to an increased risk of Alzheimer’s disease and other dementias, including vascular dementia, they found.

“Individuals weren’t just at elevated risk for dementia in the years immediately following their infection but were also at increased risk up to 25 to 30 years later,” said lead author Leah S. Richmond-Rakerd of the University of Michigan.

The increased risks were evident for both men and women across age groups, she said. And they held even after the researchers accounted for individual differences in physical and mental health and socioeconomic background.

Using New Zealand’s health registries, the research team identified serious infections via inpatient-hospital records and dementia diagnoses from inpatient-hospital records, death certificates, and prescription data. They focused on 1.7 million people born between 1929 and 1968 and followed them from 1989 to 2019.

Infections can prompt brain inflammation and thus may be a risk factor for dementia, the researchers suggested, so preventing these infections could be one way to reduce the burden of dementia.

People Living in Disadvantaged Neighborhoods Show Faster Brain Aging

Another new study links living in a poorer neighborhood to faster brain aging and increased dementia risk, regardless of a person’s income level or education.⁴

Echoing the results of smaller-scale studies of people in the United States and England, an international team led by Duke University found that New Zealanders residing in the country’s most disadvantaged areas—those with the lowest levels of income, employment, education, and transportation access—had a 43% increased risk of developing dementia over 20 years of observation.

The research team—which included the University of Michigan, Michigan State University, the University of Otago, and the University of Auckland—focused on participants in the Dunedin Study, which has tracked nearly 1,000 New Zealanders since birth, documenting their psychological, social, and physiological health through brain scans, memory tests, and cognitive self-assessments.

Study participants living in disadvantaged neighborhoods across adulthood had measurably poorer brain health as early as age 45, regardless of their own personal income or education. Poorer brain health was seen across several measurements, such as fewer or smaller nerve cells in the brain’s information processing areas, less efficient communication between brain cells, more atrophy and, potentially, microbleeds.

The brains of those in the poorest neighborhoods also looked visibly older at age 45, appearing three years older than expected for their chronological age on MRI scans. Participants from these neighborhoods also scored worse on memory tests and reported more problems with everyday cognitive demands, like following conversations or remembering how to navigate to familiar places.

The causal mechanism—or what is it about poorer neighborhoods that might harm brain health—is still unclear. But many things associated with lower-income areas could be at play, including worse air quality, lower social interaction, higher stress, and less walkability, the researchers suggest.

Targeting disadvantaged neighborhoods for dementia prevention programs could help lower dementia risk, suggests Aaron Reuben, lead author working with Duke University colleagues Avshalom Caspi and Terrie Moffitt. For now, though, he argues that just factoring in someone’s neighborhood early on is critical to catch and curb accelerated brain aging and dementia risk.

“If you want to truly prevent dementia, you’ve got to start early, because 20 years before anyone will get a diagnosis, we’re seeing dementia’s emergence,” Reuben said. “And it could be even earlier.”

Bilingualism Tied to Better Cognition at Older Ages

Speaking two languages regularly provides a cognitive advantage in older ages, finds a research team from the University of Texas Medical Branch and the University of Texas at Austin led by Brian Downer.⁵

Mexican American adults ages 65 and older who use both English and Spanish equally demonstrate better cognitive function compared with their peers who predominantly use one language, the researchers found.

The study used data from the Hispanic Established Population for the Epidemiological Study of the Elderly, which tracked a large group of U.S. Hispanic participants for 20 years.

Older adults who spoke both English and Spanish regularly scored significantly higher on a cognitive test (the Mini-Mental State Examination) at baseline compared with those who predominantly use only one language, the researchers reported.

Mexican Americans face a higher-than-average risk of cognitive decline than non-Hispanic white Americans, according to the researchers. Promoting bilingualism could be explored as a strategy to reduce dementia risk, they propose.

Nina Raffio of the University of Southern California contributed to this piece.