Beta-Amyloid: What Is Its Role in Alzheimer's Disease?

Alzheimer's is a complicated disease that experts are still working to understand. In people with Alzheimer's disease, the brain cells that process, store, and retrieve information degenerate and die. These changes in the Alzheimer's brain result from abnormal beta-amyloid proteins, which stick to and damage neurons (brain cells), ultimately permitting another protein, tau, to form inside neurons and spread between them.

Although there's no cure for Alzheimer's disease, new medications for people with mild cognitive changes or decline due to Alzheimer's are used to target beta-amyloid plaques with the goal of slowing down disease progression.

Find out what the latest evidence says about the role of beta-amyloid protein in Alzheimer's disease, how it's detected, and whether diet and exercise can make a difference.

What Is Beta-Amyloid?

The brain protein fragment beta-amyloid is a sticky compound that accumulates in the brain of someone with Alzheimer's disease, says Jagan Pillai, MD, PhD , a neurologist at the Cleveland Clinic Lou Ruvo Center for Brain Health in Cleveland.

Beta-amyloid is a small piece of a larger protein called amyloid precursor protein (APP).

What Role Does Beta-Amyloid Play in the Brain?

Beta-amyloid's role in brain function is unclear, says Dr. Pillai.

"In a healthy brain, it's broken down and cleared away by enzymes, but in people with Alzheimer's disease, it builds up and tends to clump together outside the neurons," he says.

These plaques, along with tau protein (which forms neurofibrillary tangles inside the neurons) are suspected of causing a cascade of events that eventually leads to neuron or brain cell death, causing the symptoms of Alzheimer's disease , he says.

What Causes It to Clump Together in Some People's Brains?

The exact mechanisms leading to beta-amyloid clumping are not fully understood.

"In general, the structure of the protein itself is very sticky, which isn't an issue in a healthy brain where there are normal levels and it's able to be cleared out," says Pillai.

But when the clearance mechanisms are compromised or more proteins are generated than necessary, then clumping tends to increase, he says.

What Happens in the Brain as a Result of Amyloid Clumps?

The accumulation of beta-amyloid plaques is associated with damage to brain cells and the disruption of neural communication, which progressively impairs brain functions such as memory, reasoning, and decision-making.

But the key word here is "associated." Amyloid is certainly part of the Alzheimer's disease process, but there's more to the story, says Kyan Younes, MD , a clinical assistant professor and neurologist at Stanford Health Care in Palo Alto, California.

When you look at the brain of someone with Alzheimer's under a microscope, it requires two proteins - beta-amyloid and tau protein, which is thought to occur after amyloid, says Dr. Younes.

"Amyloid alone is not clearly linked to clinical impairment (or symptoms of Alzheimer's disease)," he says.

An estimated 40 percent of people in their eighties and older have some amyloid in their brains, but don't have any Alzheimer's symptoms, he says.

Are There Tests for Beta-Amyloid Plaques in the Brain?

For many years, it was thought that a definitive diagnosis of Alzheimer's disease couldn't be made until the autopsy, after the person died, says Pillai.

Now there are three ways these proteins can be measured.

Brain scan: In an amyloid positron emission tomography (PET) scan, a special dye that binds to the amyloid protein in the brain makes plaques "light up," which allows for accurate detection of plaques.

Spinal fluid test: Performed via lumbar puncture, this test measures the amyloid and tau levels in spinal fluid and can help identify most people with Alzheimer's disease.

Blood tests: A simple blood test may soon replace other methods of testing for beta-amyloid. Researchers found that a blood test for phosphorylated tau217 (pTau217) was equivalent to the FDA-approved cerebrospinal fluid tests at identifying people with amyloid buildup, with accuracy scores for all tests between 95 and 97 percent (as compared to PET brain scans, the gold standard).

Why Do Some People With Beta-Amyloid Plaques Have No Symptoms of Alzheimer's Dementia?

Beta-amyloid plaques can accumulate gradually. A person may not have any signs of Alzheimer's for 20 years or more after their first amyloid plaques appear.

"When a person is having changes in their brain from amyloid accumulation, but they don't have symptoms, it's called preclinical Alzheimer's disease. In the preclinical Alzheimer's disease stage, if you do any of the tests mentioned above, you would find results that indicate the disease, but the person is cognitively normal," says Pillai. "The big question is: How long will this stage last?"

"Is it 15 years for some people, but 5 years for others? How can we predict when symptoms will appear, and then how quickly cognitive decline will occur? That's not clear yet," says Pillai.

Another issue that may predict when symptoms will occur is how resilient a person's brain is, or their cognitive reserve, says Younes.

"For example, people with more education may have more cognitive reserve and be less likely to show symptoms. One way to think about it is if someone has a bigger house (more education) and the rooms begin to shrink, because they started out with bigger ‘rooms,' they are still able to function at or close to their normal level," he says.

Are Beta-Amyloid Plaques the Main Cause of Alzheimer's Disease?

Beta-amyloid plaques and tau protein are considered the hallmarks of Alzheimer's disease, but they are not necessarily the sole causes. The disease is complex, as the aging brain collects many different abnormalities other than amyloid and tau.

"There are a whole host of changes that are associated with and fall under the umbrella of Alzheimer's disease, and include vascular (blood flow) changes, chronic inflammation, and changes in the immune system," Pillai says.

Can Your Diet Help to Prevent the Formation of Beta-Amyloid Plaques in the Brain?

"There is data that suggests healthy lifestyle habits may keep the brain healthier and lower the risk of Alzheimer's disease or slow down the progression," says Pillai.

Observational research has found that people who eat foods from the Mediterranean diet and the MIND diet (Mediterranean-DASH Diet Intervention for Neurodegenerative Delay) had fewer beta-amyloid plaques and tau tangles in the brain when autopsied.

People who scored the highest for sticking to the Mediterranean and MIND diets had average plaque and tau tangles in their brains typically found in much younger people.

The Mediterranean diet includes:

• Relatively little red meat
• Lots of whole grains, fruits, and vegetables
• Fish consumption at least twice a week
• Herbs as a flavoring rather than salt
• Nuts, olive oil, and other healthy fats instead of butter or other saturated fats

The MIND diet features all of the above, with an emphasis on berries and green leafy vegetables.

Does Physical Activity Impact the Formation of Beta-Amyloid Plaques?

Experts believe that what's good for the heart is good for the brain, and vigorous exercise is associated with a reduced risk of Alzheimer's disease.

The evidence for exercise's specific impact on beta-amyloid isn't as strong. A meta-analysis found that physical activity might moderately reduce beta-amyloid in middle-age and older adults, but the results weren't statistically significant.

Nonetheless, Younes encourages regular exercise.

"Studies are still exploring how exercise may impact beta-amyloid, but there's strong data that shows physical activity can reduce the risk and the level of cognitive impairment," he says.

"You need to be sweating about 30 minutes, 5 times a week to get the benefits," says Younes.

Are Drugs That Reduce Beta-Amyloid Enough to Treat Alzheimer's Disease?

There are currently three medications that target beta-amyloid.

Aducanumab (Aduhelm) is an anti-amyloid antibody intravenous (IV) infusion therapy that is delivered every month. Aducanumab is being discontinued by its manufacturer, Biogen. The company stated that people who are now receiving it by prescription will have it available to them until November 2024.

Lecanemab (Leqembi) is an anti-amyloid antibody intravenous (IV) infusion therapy that is delivered every two weeks and is approved to treat early Alzheimer's disease, including people living with mild cognitive impairment (MCI) or mild dementia due to Alzheimer's disease who have confirmation of elevated beta-amyloid in the brain.

Donanemab (Kisunla) is the latest drug to target beta-amyloid and is delivered monthly. The key difference between donanemab and lecanemab is that donanemab can be discontinued after it clears amyloid. In clinical trials about 70 percent of people taking the drug were able to stop it after 18 months.

These medications may be one piece of the puzzle, but it's likely that other treatments will be needed that target other aspects of Alzheimer's besides beta-amyloid, says Pillai.

"The evidence for the correlation between amyloid specifically and cognitive impairment is still controversial. One of the main criticisms of these medications that reduce amyloid is that they actually did not show a relationship between the reduction of amyloid and the level of cognitive impairment," says Younes.

The people in these studies need to be followed for longer, and more data is needed to know how effective the medications are, he says.

The Takeaway

Beta-amyloid is a key player in Alzheimer's disease, but it's not the entire story. Researchers are still working to understand its role in the disease process and how targeting it may slow down symptoms. If you have been diagnosed with Alzheimer's, talk with your doctor to see if any of the approved medications might be appropriate for you. But don't forget about lifestyle approaches to improving brain health: Stay active, have a healthy diet, stay socially active, and use your brain as much as possible. "The brain loves to be active and engaged," Younes says.

Editorial Sources and Fact-Checking

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy . We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

Sources

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2. Barthelemy NR et al. Highly Accurate Blood Test for Alzheimer's Disease Is Similar or Superior to Clinical Cerebrospinal Fluid Tests. Nature Medicine . February 21, 2024.
3. Estimates of Amyloid Onset May Predict Alzheimer's Progression. National Institute on Aging . February 2, 2023.
4. Agarwal P et al. Association of Mediterranean-DASH Intervention for Neurodegenerative Delay and Mediterranean Diets With Alzheimer Disease Pathology. Neurology . March 8, 2023.
5. What Do We Know About Diet and the Prevention of Alzheimer's Disease? National Institute on Aging . November 20, 2023.
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David Weisman, MD

Reviewer

David Weisman, MD, is the director of the Clinical Trial Center at Abington Neurological Associates in Pennsylvania, where he has conducted numerous clinical trials into mild cognitive impairment and Alzheimer's disease to develop disease-modifying drugs.

Dr. Weisman has dedicated his research career toward advancing new therapies for Alzheimer's disease, focusing on clinical trials for the prevention and treatment of Alzheimer's disease, mild cognitive impairment, and other dementias, and he devotes his clinical practice to memory and cognitive problems.

He received a bachelor's degree in philosophy from Franklin and Marshall College, then an MD from Penn State College of Medicine. After an internship at St. Mary's Hospital in San Francisco, he completed his neurology residency at Yale, where he served as chief resident. He then went to the University California in San Diego for fellowship training in Alzheimer's disease and other dementias.

Weisman has published papers and studies in journals such as Neurology , JAMA Neurology , Stroke , and The New England Journal of Medicine , among others.

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Becky Upham

Author

Becky Upham began her freelance writing career covering live music shows in Asheville, North Carolina, but health and wellness have been part of her professional life for almost 20 years. She's been a race director, a recruiter for Team in Training for the Leukemia & Lymphoma Society, a salesperson for a major pharmaceutical company, a blogger for Moogfest, a communications manager for Mission Health, a fitness instructor, and a health coach.

She majored in English at the University of North Carolina and has a master's in English writing from Hollins University.

Upham enjoys teaching cycling classes, running, reading fiction, and making playlists.

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