A new study suggests that a reduced or lost sense of smell could be one of the earliest warning signs of Alzheimer’s disease, appearing even before noticeable memory problems develop.
The findings, published in Nature Communications, highlight how early changes in the brain may impact sensory function at the initial stages of the disease. Researchers say that olfactory impairment may serve as an early indicator of Alzheimer’s progression.
The study found that this symptom can emerge before the more widely recognised memory-related decline begins.
How the brain is affected
Scientists from the DZNE research institute and Ludwig-Maximilians-University Munich (LMU) in Germany identified the brain’s immune system as a key factor in this process.
They discovered that immune cells called microglia may mistakenly attack nerve fibres that are essential for the sense of smell.
Disruption in smell pathways
According to the research, smell loss occurs when microglia interfere with communication between two important brain regions: the olfactory bulb and the locus ceruleus.
The olfactory bulb, located in the forebrain, processes smell signals from the nose, while the locus ceruleus in the brainstem helps regulate this system through nerve connections.
The study combined evidence from both mouse models and human samples, using brain tissue analysis and PET scans to better understand how these early neurological changes develop.
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