Like heart disease and certain cancers, the risk of developing Alzheimer’s disease can likely be predicted through certain biological markers long before any signs of the disease appear.
Researchers are fast closing in on how to identify and analyze those “biomarkers.”
But in the process, they’re also discovering just how widespread signs of future Alzheimer’s are.
Almost 47 million people in the United States over the age of 30 are estimated to have signs of “preclinical” Alzheimer’s, .
That means detectable changes that are known to eventually lead to Alzheimer’s are beginning to take place in the brain.
Researchers note it is likely years before those changes result in Alzheimer’s and impair memory or other brain functions.
Some of the 47 million, they say, won’t live long enough for the disease to appear.
Another 3.6 million Americans already had clinical Alzheimer’s in 2017.
Another 2.4 million had mild cognitive impairment (MCI) due to Alzheimer’s, an intermediate stage of the disease in which brain function is affected even before dementia sets in.
In 2060, the researchers expect, 15 million Americans will have Alzheimer’s or MCI.
Research shows potential impact
The research is the first to forecast the extent of preclinical Alzheimer’s and MCI, according to the Alzheimer’s Association.
The research points to both a growing problem and emerging opportunities.
The new statistics indicate about a quarter of the over-30 population currently could have signs of future Alzheimer’s.
And, with the percentage of that preclinical Alzheimer’s population expected to grow to 75 million by 2060, it could eventually include about 30 percent of Americans over 30.
But it also means that, if these biomarkers are accurate, patients can be targeted for diagnosis and treatment early, much like cholesterol levels and other biomarkers can indicate future risk of heart disease, diabetes, or cancer.
The primary biomarkers indicating future Alzheimer’s are the buildup of amyloid-beta proteins in the brain and the death or loss of functionality of neurons in the brain, or neurodegeneration.
If identified early enough, the hope is doctors can design interventions that can, at the very least, delay the impending dementia and Alzheimer’s as long as possible.
Currently, those interventions are limited.
Cognitive training exercises, physical exercise, and some medications have shown some signs of being effective, though the evidence is still limited.
But knowing who needs those interventions and when they might be effective is part of that progress toward treatment, said Ron Brookmeyer, PhD, professor of biostatistics at the University of California Los Angeles’ (UCLA) Fielding School of Public Health and lead author of the new study.
“We need to keep in mind how effective they are and at what point in the disease process they might be effective. Do we have interventions that could be effective at each of the points along the continuum of this long disease process?” Brookmeyer told Healthline. “If you could identify a person’s risks and screen them, what is the utility? It’s helpful for planning, but, of course, the question is, are there interventions you can do?”
In addition to pursuing better treatments, he said, the field needs to pursue better ways of predicting disease, including identifying other biomarkers and predictors, and expanding the diversity of study subjects.
His study, for instance, relied in part on data from the Mayo Clinic Study of Aging cohort, which consists of 93 percent white subjects.
An emerging portrait
But, despite the limitations, a picture of how Alzheimer’s progresses and how many people it is affecting is emerging.
That picture, according to Brookmeyer’s study, shows detectable amyloid buildup beginning as early as the 30s, but peaking in the mid-60s.
It also shows neurodegeneration starting to grow around the 40s, and peaking around age 70.
Mild cognitive impairment doesn’t generally begin until the 60s, early Alzheimer’s in the late 60s, both peaking in the mid-80s to early 90s.
For younger people, the risks are low.
“We do see a little bit of amyloid buildup in younger ages, but in terms of clinical endpoints, we don’t really see that until the 70s and 80s and above,” said Brookmeyer.
Michael Donohue, PhD, associate professor of neurology at the University of Southern California (USC) Keck School of Medicine who was not involved in the new study, pointed to that has shown around 2 percent of 30-somethings may have amyloid buildup, though that rises to around 10 percent by age 50.
The older you are by the time amyloid starts building up or other biomarkers set in, the more likely you are not to develop full-blown Alzheimer’s — though only because you’re more likely to die from something else in the course of the disease’s decades-long progression.
“The disease process is very long,” Brookmeyer said.
Of the 47 million with signs of future Alzheimer’s “many of them may never experience signs or symptoms because their natural lifespan is not long enough,” he added.
A 65-year-old woman with amyloid buildup faces a strong chance of developing Alzheimer’s.
But a 90-year-old man with amyloid buildup detected for the first time likely won’t, even when accounting for the fact that the disease progresses more quickly in older people.
“So it’s not a one size fits all,” he said. “Many of us have some brain changes going on, but we may never experience signs or symptoms.”
As for determining whether you’re one of the quarter or so Americans over 30 with signs of future Alzheimer’s, that’s also still a work in progress.
Donohue pointed to the and studies, which identify, using amyloid-detecting PET scans and spinal fluid tests, volunteers with elevated amyloid.
But, he said, insurance currently doesn’t reimburse for the PET scans and the spinal tests are mostly just used in specialized research clinics.