Alzheimer’s disease is a progressive degenerative brain disease in which beta-amyloid plaques and tau tangles accumulate, synapses and neurons are lost, and memory and thinking decline over years. It is the most common cause of dementia; the World Health Organization estimates it accounts for 60-70% of dementia cases. Dementia is the syndrome — the loss of everyday function. Alzheimer’s is one of the diseases that produce it. The biological changes start quietly: biomarker and imaging studies place that silent phase years to decades before the first noticeable symptom.
What it measures
Alzheimer’s is defined by two protein changes in brain tissue. Amyloid (beta-amyloid) fragments clump into plaques between neurons, and the tau protein that normally stabilizes a neuron’s internal scaffolding becomes abnormally phosphorylated and twists into neurofibrillary tangles inside the cell. Alongside them come activation of the brain’s immune cells, loss of synapses, and atrophy that usually begins in the memory structures of the medial temporal lobe before spreading.
In the clinic, no single test reads out “Alzheimer’s”. Diagnosis rests on the history from the person and someone who knows them, cognitive testing, and the exclusion of other causes — thyroid disease, B12 deficiency, depression, medication effects, stroke. MRI or CT shows the pattern of shrinkage and rules out alternatives. Amyloid and tau themselves can be imaged with PET or estimated from cerebrospinal fluid, and blood tests for phosphorylated tau have moved into practice. Their thresholds are assay-specific, so a number only means something against the reporting laboratory’s own reference values. For most of the disease’s history, only autopsy confirmed it outright.
Why it matters for longevity
Alzheimer’s is a healthspan problem before it is a lifespan problem. It takes away independent living — driving, finances, cooking, then washing and dressing — years before it takes away life, and it ranks among the leading causes of death in many high-income countries. Age is by far the strongest risk factor: incidence rises steeply after the mid-sixties. The full reference entry for Alzheimer’s disease goes deeper into the stages and the amyloid hypothesis.
Genetics matter but rarely decide. The APOE e4 variant is the strongest common genetic risk factor, and two copies carry more risk than one; many carriers never develop the disease, and many people who do develop it carry none. Rare inherited mutations in the APP, PSEN1 and PSEN2 genes cause early-onset familial Alzheimer’s, a small minority of cases. More women are affected than men, partly because women live longer.
What changes it
Nothing you do changes your age or the genes you inherited. A large share of the rest is at least partly modifiable: the Lancet Commission on dementia prevention estimates that close to half of dementia cases worldwide are associated with modifiable risk factors, chiefly untreated hearing loss, high blood pressure and high LDL in midlife, smoking, physical inactivity, diabetes, obesity, heavy alcohol use, depression, social isolation, head injury, air pollution, untreated vision loss and low education. “Associated” is the honest word: most of this is observational, and lowering risk across a population is not the same as preventing the disease in one person.
The levers with the most consistent support are unglamorous. Treat hearing loss. Keep blood pressure controlled from midlife on. Stay physically active. Do not smoke. Manage glucose. Sleep enough. Keep building Cognitive reserve through education, demanding work, new skills and social contact — reserve does not stop the underlying pathology, but it appears to delay when symptoms surface. Mediterranean-style and MIND eating patterns are linked to lower dementia risk in long cohorts.
On medication: cholinesterase inhibitors and memantine ease symptoms modestly and do not stop progression. Anti-amyloid antibodies given in early disease clear plaque from the brain and slowed decline modestly in their trials; they require MRI monitoring for brain swelling and small bleeds, and their availability differs by country.
Related reading
- How to Eat for Brain Health: A Cognitive Longevity Guide
- Mediterranean and MIND Diets Cut Dementia Risk
- Shingles Vaccine Linked to Lower Dementia Risk
- Chronic Inflammation and Aging: Inflammaging
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.