Groundbreaking study finds loss of smell ‘could be early sign of dementia’

According to a recent study, individuals carrying the APOE e4 gene, which is known to increase the risk of Alzheimer’s disease, are more likely to experience a decline in their ability to detect scents as they age.

The study, conducted by experts at the University of Chicago in the US, found individuals with the APOE e4 gene started to lose their sense of smell between the ages of 65 and 69.

On a scale of zero to six, measuring the number of odours they could identify, gene carriers at this age could detect an average of 3.2 smells, compared to 3.9 smells for those without the gene.

As the gene carriers reached the age of 75 to 79, their ability to identify scents became increasingly challenging. Furthermore, their sense of smell declined at a faster rate than those without the gene.

Surprisingly, thinking and memory skills were comparable between the two groups, but the gene carriers experienced a more rapid decline in their cognitive abilities over time, as expected by the researchers.

Dr Matthew GoodSmith, the lead researcher, said: “Testing a person’s ability to detect odours may be a useful way to predict future problems with cognition.

“While more research is needed to confirm these findings and determine what level of smell loss would predict future risk, these results could be promising, especially in studies aiming to identify people at risk for dementia early in the disease.

“Identifying the mechanisms underlying these relationships will help us understand the role of smell in neurodegeneration.”

To conduct the study, the research team assessed how well participants could detect an odour as well as their capacity to identify specific scents.

Additionally, DNA samples were collected to identify individuals carrying the APOE e4 gene associated with Alzheimer’s risk. Over a span of five years, the participants completed surveys at home, measuring their ability to detect odours and recognise their specific smells. Each test produced a score ranging from zero to six.

In addition to the olfactory assessments, the participants’ thinking and memory skills were evaluated twice, with a five-year gap between tests. The findings of this groundbreaking study were published in the journal Neurology.

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