A surprising early indicator of Alzheimer’s disease is a loss of smell, according to a new study. The study found that individuals with the APOE e4 gene, the same gene that actor Chris Hemsworth disclosed having two copies of, were more likely to experience a decline in their sense of smell and cognitive function compared to those without the gene. Dr. Matthew S. GoodSmith of the University of Chicago, the study’s author, stated that testing a person’s ability to detect odors could be a useful predictor of future cognitive issues.
Previous research has demonstrated a connection between the loss of smell and inflammation in the brain, which is associated with cognitive decline. The APOE gene, specifically the APOE e4 allele, is the genetic variant that significantly increases the risk of developing dementia. This gene is responsible for transporting cholesterol and other fats in the bloodstream.
A recent study published in the journal Neurology revealed that individuals with the APOE e4 gene were 37% more likely to have a diminished ability to detect odors compared to those without the gene. The study analyzed 865 participants who completed at-home surveys to evaluate their sense of smell and underwent memory and thinking assessments over a five-year period. The researchers also collected samples to identify individuals with genes linked to a higher risk of Alzheimer’s disease.
Participants with at least one copy of the APOE e4 gene scored lower on the odor detection test than non-gene carriers. Individuals between the ages of 65 and 69 with the gene detected an average of 3.2 smells, while those without the gene detected 3.9 smells. Additionally, participants between the ages of 75 and 79 with the gene experienced difficulty identifying specific odors, and once they lost that ability, their decline in cognitive function was more rapid compared to non-gene carriers.
The study suggests that the loss of smell may contribute to inflammation in the brain, a known factor in cognitive decline. However, further research is needed to confirm these findings and determine the extent of smell loss that could predict future dementia risk.
This study builds upon previous research that has established a link between smell and cognitive impairment. For instance, a study published in the Journal of Alzheimer’s Disease found that lower performance on odor identification tests was associated with a 22% higher chance of developing mild cognitive impairment, which may progress to Alzheimer’s disease.
It is worth noting that the study’s limitation is the exclusion of patients with severe dementia. Dementia is an umbrella term encompassing various progressive neurological disorders that affect memory, thinking, and behavior. Alzheimer’s disease is the most common form of dementia, accounting for 60 to 70% of cases worldwide.
The study received funding from the National Institutes of Health, National Institute on Aging, and National Institute of Diabetes and Digestive and Kidney Diseases.
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