This year, too, there is a special international theme surrounding the day: "The earlier you know, the more you can do: a dementia diagnosis matters."

Prevention

The World Health Organization (WHO) recently published an advisory report based on a comprehensive study that reviewed the existing literature. This study examined and discussed 14 modifiable risk factors that may help reduce the risk of developing dementia (see also: Livingston, The Lancet Commissions, 2024).

In this revised and updated version of the findings, many previous lifestyle recommendations remained in place: sufficient exercise, a healthy and balanced diet, avoiding being overweight, treating elevated cholesterol, high blood pressure and diabetes, and refraining from smoking and excessive alcohol consumption.

In the latest version of the report, the WHO pays more attention to sleep, air pollution, impaired vision, hearing loss, strokes, traumatic brain injuries, and the importance of social contact. A combination of measures is likely to bring the greatest benefit, the report concludes.

Diagnosis

The theme of this year's World Alzheimer's Day is early diagnosis. Why is it actually important to diagnose dementia as early as possible? Prevention matters because a significant portion of Alzheimer's risk comes down to modifiable factors, and only an early diagnosis provides enough time to address those factors before the disease manifests.

Diagnosing Alzheimer's early has changed a lot in recent years. Doctors used to wait until someone showed clear symptoms, like memory loss, before testing for the disease. Today, the focus is increasingly on detecting biological signs of Alzheimer's in the body, sometimes years before a person notices anything at all. The starting point is still usually simple memory and thinking tests carried out at the doctor's office, together with brain imaging (MRI or CT) to check for shrinkage in the areas important for memory and to rule out other problems such as a stroke or a tumor. This works, but according to the Alzheimer's Association, it has a downside: by the time these tests show something, considerable damage has often already occurred in the brain (Alzheimer Organisation | How is Alzheimer's disease diagnosed?).

Detecting early

That is why so much research is focused on detecting the disease earlier, at the biological level. Special brain scans (PET scans) can visualize two proteins linked to Alzheimer's, amyloid and tau, building up in the brain. Another type of scan can show whether brain cells in memory regions are using less energy than they should, an early warning sign. There is also a fluid test, in which a small sample is taken from around the spine, that checks for these same Alzheimer's-related proteins. And a genetic test can show whether someone carries genes that raise their risk, most notably a gene called APOE4, although carrying this gene does not mean the person will definitely develop the disease (Alzheimer Organisation | Early diagnosis).

Blood test to detect dementia

The most exciting new development is a simple blood test that looks for a protein called p-tau217. A large 2026 study found that among older adults who had no memory problems at the time of testing, those with very high levels of this protein had a 78% probability of developing cognitive problems within 10 years. Even people with moderately elevated levels had a probability of nearly 45% over that period. This is significant because it shows that a blood test, quick and far less invasive than a brain scan or a spinal fluid test, may be able to detect risk roughly ten years before anyone notices a problem (Buckley 2026, Petersen 2026).

Still, doctors are not yet ready to roll this test out widely. Levels of this protein can also be influenced by other factors, such as a person's age, kidney health, body weight, and background, which is why it isn't a perfect standalone predictor for an individual. Research so far has also focused largely on a fairly narrow group of people, so further studies are needed before the test is used more broadly. For now, doctors mainly see it as a helpful early clue that shows who should get a more detailed brain scan or fluid test, rather than something the general public should use as a routine check.

Some labs, including Quest Diagnostics, already offer this blood test commercially, which is accelerating the shift. Unlike the brain scans, however, it has not yet received full approval as a standalone diagnostic tool for routine medical use.