How Common Is Alzheimer's Really? New Study Reveals Surprising Numbers About Brain Disease in Older Adults

A groundbreaking study using blood tests has revealed that Alzheimer's disease pathology is far more common in older adults than many realize, affecting nearly two-thirds of people over 90 years old. Researchers analyzed blood samples from 11,486 Norwegian adults over age 57, using a new marker called phosphorylated tau at threonine 217 (pTau217) to detect brain changes associated with Alzheimer's disease.

What Percentage of Older Adults Actually Have Alzheimer's Pathology?

The study found a dramatic increase in Alzheimer's disease neuropathological changes (ADNCs) with age. Among people aged 58 to 69.9 years, less than 8% showed signs of these brain changes. However, this number jumps significantly in older age groups, reaching 65.2% in those over 90 years of age.

For people aged 70 and older, the researchers identified three distinct groups:

• Preclinical Alzheimer's: 10% had brain pathology but no cognitive symptoms yet
• Prodromal Alzheimer's: 10.4% showed mild cognitive impairment with underlying pathology
• Alzheimer's Dementia: 9.8% had full-blown dementia with confirmed pathology

How Does Cognitive Status Relate to Brain Pathology?

Perhaps most surprising was how the presence of Alzheimer's pathology varied across different cognitive states. Among people 70 and older with dementia, 60% actually had Alzheimer's disease neuropathological changes, meaning 40% had dementia from other causes. For those with mild cognitive impairment, 32.6% showed Alzheimer's pathology, while 23.5% of cognitively normal individuals had these brain changes without symptoms.

This research represents a major advancement because, until recently, detecting Alzheimer's pathology required invasive procedures like spinal taps or expensive brain scans. The new blood test makes it possible to study much larger populations and get a clearer picture of how common these brain changes really are.

Why Are These Findings Important for Treatment?

Meanwhile, researchers at the Medical College of Georgia are taking a completely different approach to treating Alzheimer's disease. They've received approval to begin human trials using deep brain stimulation (DBS), a treatment that involves implanting tiny electrodes in a specific brain region called the nucleus basalis of Meynert.

"The nucleus basalis of Meynert was one of the first sites implicated in Alzheimer's dementia 50 years ago," said David T. Blake, PhD, professor in the Neuroscience and Regenerative Medicine department at MCG and principal investigator of the trial. This brain region plays a crucial role in memory, attention, and cortical function, and it shrinks as cognitive abilities decline.

The Georgia team's approach uses intermittent stimulation rather than continuous stimulation. Patients will receive 10 seconds of stimulation followed by 40 seconds of rest, repeated for about an hour daily. "We're giving the brain a little interval workout," Blake explained, comparing it to how muscles need rest between sets during exercise.

Starting in January 2026, six patients between ages 65-85 with early-stage Alzheimer's will participate in the two-year trial. The treatment will be administered remotely by patients or their caregivers for 50 minutes daily. Six additional patients will serve as a control group to track normal disease progression.

The Norwegian study's findings suggest that millions more people may have Alzheimer's pathology than previously estimated, making the development of new treatments like deep brain stimulation increasingly urgent. With the National Institute on Aging predicting that Americans living with Alzheimer's will nearly double to 13.9 million over the next four decades, understanding both the true prevalence and potential new treatments becomes critical for healthcare planning.