Recent studies have identified a diminished sense of smell as a potential early warning sign of Alzheimer's disease. Researchers at the University of Chicago found that individuals who carry the APOE e4 gene, a well-established genetic risk factor for Alzheimer's, were 37% more likely to experience olfactory dysfunction by the age of 65. This decline in the ability to detect smells was observed even before any noticeable memory issues or other cognitive impairments developed.

Further investigations into the underlying mechanisms revealed that in the early stages of Alzheimer's, immune cells in the brain, known as microglia, may mistakenly attack neural connections between the olfactory bulb and the locus coeruleus—a key region in the brainstem responsible for sensory processing. This damage disrupts the brain's ability to process smells, potentially leading to anosmia (the complete loss of smell). The research suggests that olfactory dysfunction, such as a reduced sense of smell, could appear before cognitive decline, making it a potential early biomarker for Alzheimer's disease.

While experts acknowledge that a reduced sense of smell can be a normal part of aging, its occurrence alongside other risk factors, such as carrying the APOE e4 gene, may warrant further evaluation. The identification of olfactory dysfunction as a possible early indicator of Alzheimer's presents a promising opportunity for early diagnosis and intervention. Researchers are exploring simple, non-invasive at-home smell tests as tools to detect early signs of cognitive impairment, providing a potential method for identifying individuals at risk of Alzheimer's disease before clinical symptoms manifest.

The findings highlight the importance of detecting early signs of Alzheimer's, as early intervention has been shown to help manage the disease and improve quality of life for individuals at risk. Furthermore, these discoveries emphasize the need for continued research into the link between sensory functions, such as smell, and cognitive health.

This growing body of research supports the idea that a loss of smell could be more than just a typical part of aging and may instead offer a critical clue in identifying individuals who are at an increased risk for Alzheimer's disease, even before other symptoms appear. The use of smell tests in routine screenings could potentially become an important tool in the early detection of cognitive decline.

Research Paper 📄
DOI: 10.1038/s41467-025-62500-8

Sources:

• National Institute on Aging: "Olfactory Dysfunction as a Biomarker for Alzheimer's Disease" (https://www.nia.nih.gov)

• University of Chicago: "The Link Between Smell and Alzheimer's Disease" (https://www.uchicago.edu)

• Alzheimer's Association: "Early Detection of Alzheimer's Disease" (https://www.alz.org)