Study links ability to smell with dementia risk five years later

29 September 2017

Researchers in the US have published new findings showing that cognitively healthy 57 – 85 year olds who have difficulty detecting odours are more likely to develop dementia five years later.

The authors suggest that odour detection tests could be helpful for flagging up those in need of closer monitoring. The study is published on 29 September 2017 in the Journal of the American Geriatrics Society.

The study gave a smell test to 2,906 men and women, using ‘Sniffin’ Sticks’ that present a particular odour, which the volunteer is asked to identify. Five years after the initial test, researchers either assessed volunteers for dementia or spoke to a relative or friend, if the volunteer was too ill or had died.

The study found that five years after the initial smell test, 4% of volunteers reported a diagnosis of dementia. Around half of those who had been diagnosed with dementia had shown errors on their smell test five years previously, with the other half showing normal smell function. In contrast, more than three-quarters of the older adults who did not develop dementia showed normal smell testing five years earlier.

The researchers suggest that changes in smell could be an early sign of dementia and could be used to identify those people at risk of the condition, who may be in need of closer monitoring.

Rosa Sancho, Head of Research at Alzheimer’s Research UK, said:

“Smell is our most primitive sense and humans can distinguish up to a trillion different odours. This study links difficulties in recognising smells with a greater dementia risk five years later, adding to existing evidence that smell could act as an early warning sign for the condition. Scent cells in our noses feed directly into the brain and we know that diseases like Alzheimer’s can start to damage the brain around a decade before symptoms show. While it’s possible that early damage caused by diseases like Alzheimer’s could interfere with a person’s ability to smell, it isn’t always an early symptom of dementia and there are many reasons why someone’s sense of smell could change.

“Smell tests are already being explored in our Insight 46 study, a landmark UK research study of 500 people aged 71, to understand more about changes in smell in ageing and dementia. While smell tests could help to flag up wider concerns, they’d need to be used alongside other, more specific diagnostic tests if they were to aid the early detection of dementia in future.”