Alzheimer’s disease is a progressive brain disorder that slowly destroys memory, thinking skills, and eventually the ability to carry out basic daily tasks. It is the most common cause of dementia, accounting for 60% to 80% of all dementia cases. An estimated 7.1 million Americans are currently living with symptoms, and that number is projected to nearly double to 13.9 million by 2060.
How Alzheimer’s Differs From Normal Aging
Everyone forgets things occasionally, and that’s normal. You might blank on someone’s name but recall it later, or misplace your glasses from time to time. These lapses don’t interfere with your ability to work, live independently, or maintain relationships.
Alzheimer’s is different. The memory loss disrupts daily life and gets worse over time. Early signs include asking the same questions repeatedly, forgetting common words mid-sentence, substituting the wrong word entirely (saying “bed” when you mean “table”), taking much longer to follow a familiar recipe, putting belongings in strange places like a wallet in a kitchen drawer, and getting lost while driving or walking in a familiar neighborhood. Changes in mood or behavior with no obvious cause can also be an early signal.
What Happens Inside the Brain
Two types of abnormal protein buildup drive the disease. The first involves clumps of a protein fragment called amyloid beta that accumulate between nerve cells. Even before those visible clumps form, smaller soluble pieces of amyloid beta begin disrupting communication between neurons, particularly at the synapses where signals pass from one cell to the next. This synaptic damage is now understood to be a key driver of early cognitive decline.
The second involves twisted fibers of a protein called tau that build up inside neurons. Normally, tau helps stabilize the internal transport system that moves nutrients and signals through nerve cells. When tau becomes tangled, that transport system collapses, and the neurons gradually lose function and die. As more neurons are lost across wider areas of the brain, symptoms progress from mild forgetfulness to profound disability.
Alzheimer’s vs. Other Types of Dementia
Dementia is the umbrella term for significant cognitive decline. Alzheimer’s is the largest category underneath it, but several other types exist. Vascular dementia, the second most common form (about 5% to 10% of cases), results from reduced blood flow to the brain, often after strokes. Symptoms depend on which part of the brain is affected and tend to worsen in a stepwise pattern rather than gradually.
Lewy body dementia is caused by abnormal protein deposits that affect brain chemistry. It can cause memory loss like Alzheimer’s but often includes movement problems such as stiffness or trembling, visual hallucinations, daytime sleepiness, and staring spells. Frontotemporal dementia affects the front and side regions of the brain, leading to personality changes, difficulty planning, and socially inappropriate behavior, sometimes before any memory problems appear. It’s also possible to have mixed dementia, where more than one type is present at the same time.
The Five Stages of Progression
Alzheimer’s generally moves through five stages, though the pace varies from person to person.
The first stage is preclinical. Changes are happening in the brain, but there are no noticeable symptoms. This stage can last years or even decades and is typically only detected in research settings through specialized testing.
The second stage is mild cognitive impairment. Memory lapses become more frequent, such as forgetting recent conversations or missing appointments. Judging how long a task will take or figuring out the steps to complete it becomes harder. These changes are noticeable but don’t yet prevent someone from working or managing daily responsibilities.
In the mild dementia stage, problems become obvious to family and friends. Paying bills, preparing meals, and navigating familiar places all become increasingly difficult. This is often the point at which a formal diagnosis is made.
Moderate dementia brings more significant confusion. People in this stage may not remember their own address, become disoriented about the time or date, and need help choosing appropriate clothing or managing hygiene. Personality and behavioral changes often become more pronounced.
In severe dementia, communication fades to a few words or phrases, and eventually speech may be lost entirely. Full-time assistance is required for eating, dressing, and all personal care. The body’s basic functions, including swallowing and bladder control, gradually decline.
Genetics and Risk Factors
The strongest known genetic risk factor is a gene variant called APOE e4. Carrying one copy of this variant increases Alzheimer’s risk and is associated with developing symptoms at an earlier age. Carrying two copies raises the risk further. That said, having APOE e4 is not a guarantee. Some people with two copies never develop the disease, and many people who get Alzheimer’s carry no copies at all.
Genetics is only part of the picture. Nearly 45% of all dementia cases may be preventable or delayable through lifestyle changes. The most impactful modifiable risk factors include physical inactivity, unmanaged diabetes, high blood pressure, untreated hearing loss, excessive alcohol use, and smoking. Hearing loss is a particularly underappreciated risk factor. Researchers believe it forces the brain to work harder to process sound, drawing resources away from thinking and memory. It also tends to reduce social engagement, which itself is protective for brain health. Using hearing aids may lower the risk.
Regular physical activity (at least 150 minutes per week) helps protect both the cardiovascular system and the brain. Managing blood pressure keeps blood vessels healthy and reduces stroke risk, which in turn protects against vascular damage in the brain. Quitting smoking and limiting alcohol reduce several overlapping risk factors at once.
How Alzheimer’s Is Diagnosed
Diagnosis has traditionally relied on clinical evaluations, cognitive testing, and brain imaging. But clinical evaluations alone are only about 73% accurate at specialty memory clinics and just 61% accurate in primary care settings. A newer blood test is changing that. Called PrecivityAD2, it measures specific forms of amyloid beta and a type of tau protein known as p-tau217. Across multiple studies, this blood test predicted an Alzheimer’s diagnosis with 88% to 92% accuracy, a substantial improvement over clinical judgment alone. Measuring p-tau217 by itself performed nearly as well as the combined panel.
This kind of blood-based testing is making earlier and more accurate diagnosis increasingly accessible, which matters because the newest treatments work best when started early.
Current Treatment Options
For decades, Alzheimer’s medications could only manage symptoms without slowing the disease itself. That changed with a new class of treatments that target and clear amyloid buildup in the brain. The most recently approved option, donanemab (sold as Kisunla), is given as an intravenous infusion every four weeks. In clinical trials involving over 1,700 patients, those receiving the treatment showed a statistically significant reduction in cognitive and functional decline compared to placebo over 76 weeks.
These newer treatments are approved for people in the mild cognitive impairment or mild dementia stage, not for advanced disease. They come with notable risks, particularly brain swelling or small brain bleeds known as amyloid-related imaging abnormalities. People who carry two copies of the APOE e4 gene variant face a higher chance of these side effects, so genetic testing is done before treatment begins. Infusion reactions such as headache, nausea, and blood pressure changes can also occur.
Older medications that boost chemical messengers in the brain remain in use to help with memory and thinking symptoms, though they don’t change the course of the disease. Non-drug approaches, including structured daily routines, physical exercise, social engagement, and caregiver support, remain essential parts of managing life with Alzheimer’s at every stage.