Impaired sense of smell may predict memory decline and risk of dementia

Decreased ability to identify smells could be an early indicator of cognitive impairment and dementia.

This is according to research presented today (Tuesday 26 July) at the Alzheimer’s Association International Conference (AAIC) in Toronto.

Two studies looked at changes in sense of smell and compared it to two established characteristics of dementia – the amount of amyloid protein in the brain and the size of a brain area that is important for memory.

Researchers at Columbia University Medical Center used the University of Pennsylvania Smell Identification Test (UPSIT) to test sense of smell in 397 older people without dementia. They also took brain scans and looked for thinning of the entorhinal cortex, an area of the brain important for memory that is affected early in Alzheimer’s disease.

During the four-year follow-up period, 50 participants developed dementia. Impaired sense of smell and thinning of the entorhinal cortex were both significantly associated with transition to dementia, sense of smell also predicted cognitive decline.

A second study, also conducted at Colombia University Medical Center, compared how well a declining sense of smell is able to predict cognitive decline, by comparing it to a well-established marker of Alzheimer’s disease – amyloid protein in the brain. The researchers used the UPSIT score to rate sense of smell and brain imaging or spinal fluid analysis to determine the level of brain amyloid protein in 84 people.

At follow-up periods of either two or four years, 67% of participants showed signs of memory decline. While the amount of brain amyloid present, but not odour identification, predicted memory decline, those with an impaired sense of smell were three times more likely to have memory problems.

Dr Doug Brown, Director of Research and Development at Alzheimer’s Society, said:

'These studies add to growing evidence that sense of smell can be affected in the early stages of dementia. However, there are many reasons why people might lose their sense of smell – the natural ageing process, some medications, and more than 60 medical conditions can all affect someone’s ability to sniff out certain smells.  

'While less invasive tests for dementia would be incredibly useful, we need larger studies to test how reliably sense of smell can be used as an early predictor of memory decline and dementia.

'Most people experience some sensory loss as they age, so anyone with an impaired sense of smell shouldn’t be immediately worried about dementia, but if you have noticed changes to your sense of smell at any age, it's advisable to speak to your GP.'