Dementia risk: German researchers find one symptom that appears early in those with Alzheimer's disease

A study titled "Early Locus Coeruleus Noradrenergic Axon Loss Drives Olfactory Dysfunction in Alzheimer's Disease" by a group of German researchers explains an early symptom of Alzheimer's disease, a common form of dementia. According to the World Health Organisation (WHO), dementia affects over 55 million people worldwide in 2025, with numbers projected to nearly double every 20 years due to aging populations. About 1 in 9 people aged 65 and older has dementia, with prevalence increasing sharply after the age of 75. Women represent nearly two-thirds of those affected. The global prevalence among adults aged 65+ rose from about 19 million in 1991 to 49 million in 2021, a 160% increase.

​Heart health: Why listening to your breath could save your life

​Frozen peas and carrots recalled in 7 US states over Listeria risk – here’s what you need to know

​Rare and deadly 'kissing bug' spreading across US; All about the Chagas disease that can cause fatal heart attacks and strokes​

In simple terms, the researchers discovered that in Alzheimer's, brain immune cells called microglia mistakenly destroy important nerve connections from a brain region called the locus coeruleus to the olfactory bulb, which is responsible for processing smells. This destruction happens early on, before memory loss appears. They found that the nerve cells in the locus coeruleus send signals to the olfactory bulb, but because of changes in the nerve cell membranes, they emit an "eat-me" signal. This signal triggers microglia to remove those nerve connections by mistake.

Loss of smell, or olfactory dysfunction, is an early sign linked to dementia, especially Alzheimer’s disease. The brain regions responsible for processing smells, including the olfactory bulb and related nerve pathways, are among the first affected by dementia-related brain changes. Damage to these areas disrupts smell perception before memory problems appear. This early olfactory loss reflects underlying neurodegeneration and can help predict disease progression. Identifying smell loss in patients may allow earlier diagnosis and intervention in dementia, making it a valuable clinical marker for detecting neurodegenerative diseases.

The recent increase in dementia prevalence is largely driven by several modifiable risk factors. These include hypertension (high blood pressure), diabetes, obesity, smoking, physical inactivity, depression, excessive alcohol consumption, hearing loss, and social isolation. Low educational attainment and poor sleep quality are also significant contributors. These factors often coexist and can amplify dementia risk. Managing these through lifestyle changes, such as regular physical activity, healthy diet, quitting smoking, controlling blood pressure and blood sugar, and maintaining social engagement, can reduce or delay dementia onset. Even small steps count. Addressing multiple factors simultaneously may have the greatest impact on reducing dementia risk globally.