New blood tests that might predict Alzheimer’s years before symptoms begin may sound tantalizing for people who worry about later-in-life dementia. But doctors say they aren't quite ready yet – and besides, you don’t need a test before trying to lower your risk.
The U.S. Food and Drug Administration has cleared four blood tests to help doctors diagnose whether Alzheimer’s – not another kind of dementia or something else – is behind someone’s memory problems or other cognitive symptoms. Some laboratories and online services offer their own tests. Faster diagnosis can help people with early-stage Alzheimer’s qualify for drugs that can modestly slow the worsening of their symptoms.
Yet dementia specialists say people without symptoms also seek those tests even though they’re neither approved nor recommended for that population.
For now, "the worried well should not be getting those tests” outside of a research study, stressed testing expert Nicholas Ashton, of Arizona’s Banner Health.
Instead, focus on addressing potentially preventable brain risks. One large study found people who reached middle age without high blood pressure, diabetes and smoking lived dementia-free for a lot longer – nearly 13 years longer – than people with all three of those common health problems in their 50s.
"Be aggressive,” advised Dr. Josef Coresh of NYU Langone Health, the study’s senior author. Even delaying those risky conditions "has a huge payoff.”
Like many people who have watched a loved one succumb to Alzheimer’s, Mark Yost wonders about his own risk even though he doesn’t have symptoms.
"I want to know what my status is,” said Yost, 60, of Phoenix. And if signs of trouble develop, "what I can do about it to either avoid it or slow it down.”
It's not clear what causes Alzheimer's, but its telltale markers are abnormal forms of two proteins. Sticky beta-amyloid can build into brain-clogging plaque over decades, eventually spurring neuron-killing tau tangles that lead to symptoms. Blood tests that measure a tau type called p-tau217 seem particularly good at reflecting amyloid buildup in people with symptoms.
As for the symptom-free, a study led by Mass General Brigham researchers found older adults with very high p-tau217 levels had a 38% risk of developing cognitive impairment within five years and a higher risk over 10 years.
Here’s the rub: A "positive” test result is just a risk factor, not a guarantee someone will later develop Alzheimer’s, Ashton cautioned. Lots of older adults harbor high levels of amyloid but never show cognitive trouble. And while negative test results seem pretty reliable, a positive test sometimes is wrong, a so-called false positive.
Yost volunteered for a Banner blood test study that included cognitively normal people and learned his result was "intermediate,” defined as maybe having some amyloid but not a worrisome "elevated” level.
Yost found the uncertainty "a little disappointing” and something to watch as he gets older, while pursuing brain-healthy steps like exercise and a mentally stimulating genealogy hobby.
A major trial last year found that healthier habits slowed age-related cognitive decline in older adults who were at increased risk of developing dementia. Among the steps: A half-hour of moderately intense exercise four times a week, twice-weekly resistance training and following the MIND diet, which stresses lots of leafy greens and berries, whole grains, poultry and fish.
Dementia experts also advise getting enough sleep, avoiding social isolation, treating hearing loss and exercising your brain, not just your body. They say middle age is a key time to act.
As for those extra 13 dementia-free years, the NYU study reinforces that what's good for the heart is good for the brain.
Coresh's team analyzed health records of more than 12,000 people who had been tracked for decades since they were, on average, age 56. High blood pressure, Type 2 diabetes and smoking can damage blood vessels that feed the brain and fuel inflammation. Those who entered the study without those three problems fared best, but avoiding one or two was helpful. Even people who carry the APOE4 gene, which increases the risk of later-in-life Alzheimer's, still benefited from a healthier middle age.
Other studies also have shown that aggressively treating high blood pressure helps brain health.
"Be very serious with your physician about the value of lowering it as early as possible for as many years as possible,” Coresh said.
As for those Alzheimer's blood tests, stay tuned. Clinical trials are underway to tell if drugs now used to treat Alzheimer's might also help certain people before they develop symptoms – findings that could change testing advice.
