Condition: Demenz & Alzheimer

What It Is

Dementia is a lasting decline in memory, thinking or judgment severe enough to interfere with everyday life. It covers several diseases, each with a different cause and course, and telling them apart changes what helps.

Alzheimer's disease is the most common. Amyloid plaques and tau tangles build in the brain over years, usually starting with short-term memory and word-finding. The changes begin in midlife, long before any symptom, so what you do in your forties and fifties affects the risk decades later.

Vascular dementia comes from strokes, small-vessel disease and poor blood flow, and it often progresses in steps, with slowed thinking and trouble planning as much as memory loss. It shares its risk factors with heart disease, which makes it the most preventable of the group.

Lewy body dementia brings fluctuating attention, visual hallucinations, movement changes like Parkinson's, and vivid acting-out of dreams. It matters to recognize early, because certain antipsychotic drugs can cause severe reactions in these patients.

Mixed dementia is more than one process at once, most often Alzheimer's changes together with vascular damage. In people over 80 this combination is more common than any single pure type, part of why vascular risk factors matter even for Alzheimer's.

Mild cognitive impairment sits one step earlier: measurable memory or thinking changes greater than normal aging, with daily life still largely intact. It is a stage, and it does not always progress. Some people go on to dementia, some stay stable for years, and a meaningful number return to normal. That last outcome is most likely when a reversible cause is found and treated. It is the point at which attention pays off most.

Whatever the type, dementia tracks the health of the whole body more than the brain alone. The same process that stiffens and narrows arteries drives vascular damage in the brain. That is why vascular care ranks among the better-supported levers for the mind.

Prevention: The Risk You Can Change

The strongest lever in dementia is the risk you can change, and there is more of it than most people are told. The Lancet Commission's 2024 report estimates that about 45% of dementia cases are tied to fourteen modifiable risk factors acted on across a lifetime.

The larger contributors it models fall across three stages of life:

• Early life: less education.
• Midlife: hearing loss, high LDL cholesterol, high blood pressure, obesity, heavy drinking and head injury.
• Later life: smoking, depression, physical inactivity, diabetes, air pollution, social isolation and untreated vision loss.

Untreated vision loss and high cholesterol were added since the 2020 report. That 45% is a population estimate; it does not promise any one person a specific outcome. It assumes the links are causal and that each factor could be fully removed. The factors overlap, and 45% is the most that could ever be avoided in theory, far more than any one person can subtract from their own risk. These levers count for most in midlife, though starting later still helps.

Much of the evidence for the individual levers is observational, showing a pattern without proving cause. The people who exercise, eat well and stay connected also tend to be wealthier, better educated and healthier in ways that independently lower dementia risk. Early brain changes can also alter how people live years before a diagnosis.

Blood pressure has the strongest trial evidence behind it.

In the SPRINT MIND trial, driving systolic pressure toward 120 rather than 140 lowered the risk of mild cognitive impairment by about 19%.

The combined outcome of impairment or dementia fell by about 15%. Dementia alone fell in the same direction but did not reach statistical significance. The trial was stopped early once the heart benefit was clear, so it was left underpowered for dementia specifically.

Hearing loss is the single largest factor on the Lancet list, and correcting it is low-risk. Across the whole ACHIEVE trial, hearing aids did not slow three-year cognitive decline more than health education. In a prespecified group at higher risk, older adults with more risk factors, the same intervention slowed decline by about 48%. The overall result was null and the 48% comes from one subgroup, so it needs confirmation, but hearing aids help communication and mood in any case.

Movement, diet and sleep each point the right way, with mixed trial support.

Long cohort studies link regular activity to lower dementia risk. A two-year structured exercise program in previously sedentary older adults, the LIFE trial, did not improve thinking more than health classes. Exercise still helps mood and the blood vessels the brain depends on. It has not been shown to reverse decline once that decline has begun late in life.

A Mediterranean or MIND eating pattern was linked in a large cohort to about 53% less Alzheimer's in the closest followers. A three-year randomized trial of the MIND diet found no cognitive benefit over the control diet. The pattern is heart-safe, and its cognitive benefit is better supported by observation than by trial.

Sleeping six hours or less in midlife tracked about 30% more dementia over 25 years in the Whitehall II study. The diseases that cause dementia disturb sleep years before diagnosis, so some of that link likely runs the other way.

The clearest single signal that several levers together help comes from the Finnish FINGER trial. It combined diet counseling, exercise, cognitive training and vascular monitoring for two years. Overall cognitive scores were modestly better than with general advice. Larger and longer trials to confirm a lasting effect on dementia itself are still running.

Where the Medicines Fit

No drug yet halts the underlying disease or turns it back. Cholinesterase inhibitors, the drugs donepezil, galantamine and rivastigmine, give a modest improvement in memory and daily function for a time. Across randomized trials they lifted cognition by about 2.4 points on the 70-point ADAS-Cog scale over six months, with smaller gains in daily function and behavior. The three perform similarly. They ease symptoms; they do not slow the underlying disease, and the benefit lasts only while the drug is taken. Nausea, diarrhea, a slow heart rate and appetite loss are common enough that some people stop.

For moderate-to-severe disease, memantine is sometimes added, again for a modest symptomatic effect. In Lewy body dementia the cholinesterase inhibitors can help attention and hallucinations specifically.

The anti-amyloid antibodies are the newest and the most debated. Both clear amyloid from the brain, and both modestly slow early Alzheimer's disease. Lecanemab slowed decline on the CDR-SB scale by 27% over 18 months in early disease, a difference of 0.45 points on an 18-point scale (1.21 against 1.66 on placebo). Donanemab slowed decline by about 35% in people with lower tau and about 22% across the whole group on a combined disease scale over the same period.

The safety concern is serious. Brain swelling, called ARIA, occurred in 12.6% of people on lecanemab and about 24% on donanemab. Small bleeds are common alongside it. Most cases cause no symptoms and show up only on a scan, though some are serious; donanemab's trial recorded three deaths linked to the drug. The risk is higher in people carrying two copies of the APOE4 gene. The antibodies are used only in early, confirmed Alzheimer's, with genetic testing and repeated MRI scans. The decision is made with a specialist who weighs a fraction of a point of slowing against the swelling and bleeding risk. Whether the benefit is large enough to be worth it in daily life is contested.

Much of living well with dementia is not about drugs. Treating pain, constipation, poor sleep and infection often settles agitation better than any sedative. Routine, orientation, music and familiar company help.

What Does Not Help, and What to Rule Out First

A large industry sells prevention that the evidence does not support. Ginkgo biloba is the clearest example. A trial gave it to more than 3,000 adults aged 75 and over for about six years. It did not lower the rate of dementia or Alzheimer's at all. Coconut oil, most nootropics and the supplements marketed for brain health have no trial evidence for preventing Alzheimer's or slowing its course. A few carry their own risks.

Brain-training apps improve the game itself and very similar tasks, with little measured carryover to everyday thinking. Demanding, varied learning (a language, an instrument, a craft) asks more of the brain.

One step comes first when thinking changes: rule out the causes that are reversible. Low vitamin B12, an underactive thyroid, depression, sleep apnea, heavy alcohol use and certain medications can all mimic or worsen dementia. Normal-pressure hydrocephalus is a treatable build-up of fluid around the brain. It brings a triad of unsteady walking, incontinence and cognitive slowing, and can improve with treatment. A slow change in thinking calls for a doctor's visit and a thorough first workup before any dementia diagnosis is accepted.

Go Deeper

• High blood pressure: how to measure it right and what lowers it, the best-supported dementia lever and a heart protector in its own right.
• Hearing protection: guarding the hearing whose loss is the single largest modifiable risk factor.
• Neuroplasticity: the adult brain's capacity to form new connections through demanding learning, exercise and sleep, including the year of walking that regrew the memory hippocampus about 2%.
• Mediterranean diet: the eating pattern behind the diet findings here, plate by plate.
• Type 2 diabetes: the metabolic and vascular pathway that reaches the brain, and how to change it.
• Insulin and glucose: the biology linking blood sugar, blood vessels and cognition.

The Chinese Medicine View