Alzheimer’s disease is the most common form of dementia, accounting for 60% to 80% of all cases. It is the seventh leading cause of death among U.S. adults, and the risk climbs steeply with age: about one in 13 people between 65 and 84 live with Alzheimer’s, rising to one in three among those 85 and older.
What Happens in the Brain
Alzheimer’s involves two types of protein buildup that progressively damage brain cells. The first is a sticky protein fragment that clumps into plaques between neurons. These plaques, and especially the smaller dissolved forms of the protein circulating before they clump, are toxic to the connections between brain cells. They disrupt communication at synapses, particularly in the early stages of the disease.
The second protein normally helps stabilize the internal scaffolding of neurons. In Alzheimer’s, it becomes chemically altered, detaches from its scaffolding role, and collapses into tangled fibers inside the cell. These tangles choke off the cell’s internal transport system, eventually killing it. The damage follows a predictable path through the brain, starting in areas involved in memory formation, then spreading through regions responsible for emotion and complex thinking, and finally reaching the outer brain regions that control higher-level cognition. The plaque buildup appears to accelerate the spread of tangles, and the two processes together create a cycle of worsening damage.
Early Warning Signs vs. Normal Aging
Everyone forgets things as they get older. Misplacing your car keys, blanking on an acquaintance’s name, or struggling to find a word before remembering it later are all normal. With typical aging, your overall memory, language ability, and accumulated knowledge stay intact.
The signs that point toward Alzheimer’s are different in character, not just frequency. Getting lost in a familiar neighborhood, using unusual substitute words for everyday objects, forgetting the name of a close family member, losing old memories that were once well established, and being unable to complete routine tasks independently are all red flags. The distinction is that normal aging involves occasional retrieval glitches, while Alzheimer’s erodes the stored information itself.
How Alzheimer’s Progresses
The disease begins long before anyone notices symptoms. Brain changes can be underway for years or even decades during what researchers call the preclinical stage. During this period, there are no outward signs.
The first noticeable phase involves mild changes in memory and thinking. You might have trouble remembering information that would normally come easily, but the changes aren’t severe enough to interfere with work or relationships. Over time, these lapses deepen into difficulty managing finances, planning meals, navigating familiar places, and following conversations. Personality changes, confusion about the time or date, and withdrawal from social activities are common in the middle stages.
In the late stage, the disease affects basic physical functions. Muscles become rigid, swallowing becomes difficult, and bladder and bowel control is lost. Some people eventually cannot sit up or hold their head without support. On average, people with Alzheimer’s live between 3 and 11 years after diagnosis, though some live 20 years or more. The wide range reflects how early the diagnosis is made and individual differences in overall health.
Who Is Most at Risk
Age is the single biggest risk factor. Less than 10% of Alzheimer’s cases develop before age 65. A specific gene variant called APOE ε4 is the most well-known genetic risk factor, and carrying it is also linked to developing the disease at a younger age. That said, many people who carry the variant never develop Alzheimer’s, and many who develop it don’t carry the variant.
Rare mutations in three other genes cause a hereditary form of the disease that strikes before age 65, sometimes much earlier. A child with a biological parent who carries one of these mutations has a 50% chance of inheriting it, and those who do have a very high probability of developing the disease.
Several lifestyle and health factors also influence risk: high blood pressure, physical inactivity, poor diet, smoking, alcohol misuse, poor sleep, social isolation, untreated hearing loss, depression, and history of traumatic brain injury. These are meaningful because, unlike age and genetics, they can be addressed.
How Alzheimer’s Is Diagnosed
Diagnosis has shifted toward biology. Updated criteria from 2024 define Alzheimer’s based on measurable biological markers rather than symptoms alone. Blood-based tests can now detect the signature proteins of the disease, making earlier and more precise diagnosis possible. For now, these biomarker tests are used to evaluate people who already have symptoms, not for screening in people who feel fine.
Current Treatment Options
Two newer therapies target the protein plaques in the brain and work to clear them. These are the first treatments designed to slow the underlying disease process rather than just manage symptoms. In clinical trials, plaque removal was measured with brain imaging scans, and treatment was stopped once plaque levels dropped below a target threshold. These therapies are approved for adults with Alzheimer’s and represent a shift from earlier medications that could only temporarily ease memory and thinking symptoms without affecting the disease itself.
Other Common Types of Dementia
Vascular dementia is the second most common type, caused by reduced blood flow to the brain from strokes or damage to small blood vessels. Its main risk factors are high blood pressure, diabetes, and existing cardiovascular disease. Most cases are not inherited.
Dementia with Lewy bodies is characterized by abnormal protein deposits in the brain and is relatively common in older adults, accounting for 15% to 20% of cases in hospital autopsy studies. Frontotemporal dementia is rarer overall but disproportionately affects younger people, making up 10% to 20% of dementia cases diagnosed before age 65. About 14% of frontotemporal dementia cases are caused by an inherited gene mutation. It’s also worth noting that many people have mixed dementia, where Alzheimer’s coexists with vascular damage or Lewy body changes, which can complicate both diagnosis and treatment.