Alzheimer’s disease is caused by complex changes in the brain involving abnormal proteins, aging, genes, and health and lifestyle factors that damage and eventually kill brain cells.

What happens in the brain

In Alzheimer’s, certain proteins misbehave and build up in and around nerve cells.

  • Amyloid plaques : Clumps of a protein called amyloid build up between brain cells and form sticky “plaques,” which interfere with how brain cells communicate.
  • Tau tangles : Another protein, tau, twists into abnormal “tangles” inside brain cells and disrupts their internal transport system.
  • Over time, these plaques and tangles damage and kill neurons, leading to brain shrinkage and the memory and thinking problems we recognize as Alzheimer’s.

You can think of it like a city where roads are blocked (plaques) and power lines are twisted and broken (tangles), so neighborhoods gradually stop working.

Aging and the brain

Age is the strongest known risk factor, even though it is not a direct “cause.”

  • Most people with Alzheimer’s are over 65, and risk rises sharply with each decade of life.
  • As we age, the brain becomes less efficient at clearing abnormal proteins and repairing damage from inflammation, oxidative stress, and blood vessel problems.

Still, Alzheimer’s is not an inevitable part of aging; many older adults never develop it.

Genetics and family history

Genes influence how likely someone is to develop Alzheimer’s, but they work in different ways.

  • Rare “causal” gene variants : Changes in three genes — APP, PSEN1, and PSEN2 — can directly cause early-onset Alzheimer’s (often before age 65) in some families.
  • Risk genes : The APOE ε4 gene does not guarantee Alzheimer’s, but it increases risk and may lead to earlier onset.
  • Having a parent or sibling with Alzheimer’s increases your risk, partly due to shared genes and partly due to shared environment and lifestyle.

Most people who get Alzheimer’s do not have a single “cause gene”; instead, they have a mix of genetic and non-genetic risks.

Health and lifestyle factors

Researchers see Alzheimer’s less as one sudden event and more as a long-term result of many small hits to the brain—especially to its blood vessels and metabolism.

Factors that appear to increase risk include:

  • Heart and blood vessel problems :
    • High blood pressure, high cholesterol, heart disease, and stroke can damage blood vessels in the brain and are linked to a higher risk of Alzheimer’s.
  • Metabolic issues :
    • Type 2 diabetes, obesity, and insulin resistance are associated with more amyloid plaques and tau tangles and higher dementia risk.
  • Lifestyle habits :
    • Physical inactivity, smoking, unhealthy diet, and heavy alcohol use are all linked to increased Alzheimer’s risk.
  • Sleep :
    • Chronic poor sleep or sleep disorders can interfere with the brain’s “clean-up” of waste proteins, including amyloid.
  • Social and mental activity :
    • Social isolation, low levels of mental stimulation, and “mental apathy” (not engaging the mind) are associated with higher risk, while mentally and socially active lifestyles are linked with lower risk.

These are often called “modifiable risk factors” because improving them may reduce risk or delay onset, even though they cannot guarantee prevention.

Other conditions and triggers

Certain medical conditions or life events can also affect risk.

  • Head injuries :
    • A history of severe traumatic brain injury, especially in mid or later life, is linked with a higher risk of developing Alzheimer’s or other dementias.
  • Hearing and vision loss :
    • Untreated hearing loss and vision loss are associated with increased risk, possibly because they add cognitive strain and reduce social engagement.
  • Depression and mental health :
    • Untreated depression and chronic stress are associated with higher dementia risk, although it is still being studied whether they are causes, early signs, or both.
  • Down syndrome :
    • People with Down syndrome have an extra copy of chromosome 21, which includes the APP gene, leading to extra amyloid buildup and a much higher chance of developing Alzheimer’s.
  • Air pollution :
    • Long-term exposure to air pollution is emerging as a possible risk factor, likely through inflammation and vascular damage in the brain.

Why there is no single “cause”

Scientists now talk about Alzheimer’s as the result of a long, slow interaction between genes , aging , health conditions , environment , and lifestyle.

  • One person might have strong genetic risk but excellent heart health and never develop dementia.
  • Another person might have modest genetic risk but heavy vascular and metabolic problems and develop Alzheimer’s earlier.
  • Current evidence suggests it is the combination of risk factors in someone who is biologically susceptible that leads to the disease.

This is also why treatments have been so hard to develop: by the time symptoms appear, many different processes have been damaging the brain for years.

What we know about prevention

There is still no guaranteed way to prevent Alzheimer’s, but several approaches are considered brain-healthy and may lower risk or delay onset.

Common recommendations include:

  • Keep blood pressure, cholesterol, and blood sugar in a healthy range.
  • Stay physically active (aerobic exercise plus strength training, as appropriate for your health).
  • Do not smoke and limit alcohol.
  • Eat a balanced pattern such as a Mediterranean-style or similar heart-healthy diet.
  • Prioritize good sleep and treat sleep disorders.
  • Stay mentally active (learning, reading, puzzles, new skills) and socially connected.
  • Treat depression, hearing loss, and vision problems rather than ignoring them.

These steps do not guarantee that Alzheimer’s will be avoided, and many people develop it despite doing “everything right,” but they support overall brain and body health and are strongly encouraged.

Mini FAQ: quick scoop

  • Is Alzheimer’s caused by plaques and tangles?
    • They are central features of the disease and strongly linked to cell death, but why they form in the first place is influenced by genes, aging, and health factors.
  • Is it just inherited?
    • Only a small fraction of cases are caused by clear-cut gene mutations; most involve a mix of genetic vulnerability and life-long exposures and habits.
  • Can lifestyle changes cure it?
    • No. Lifestyle changes may lower risk or delay onset, but they do not cure existing Alzheimer’s.

Information gathered from public forums or data available on the internet and portrayed here.