Olfactory Dysfunction is Associated with Mild Cognitive Impairment (MCI)

 This article is written based on the presentation done by Prof Wang De Yun at the NUS Psychiatry Symposium on Ageing-in-Place held on 27 Apr 2023.

Olfactory impairment, or more commonly referred to as sense of smell, is ageing related. The ability to detect and identify smell has also long been linked with cognitive decline in older adults. However, there remains questions on its association with mild cognitive impairment (MCI) and by extension, dementia.


As part of the Yeo Boon Khim Mind Science Centre’s Community Health and Intergenerational (CHI) Study, Prof Wang De Yun from NUS Department of Otolaryngology, conducted a study to assess the olfactory function of community-dwelling older adults in Singapore and its link with their cognitive function. For this study, researchers at NUS developed a localised version of the nine-item smell test to better screen the population. 

Read more below!

Smell ability as a predictive tool for Cognitive Impairment

When it comes to modifiable risks of dementia, the focus is often on vision and hearing impairments rather than smell impairment. Nonetheless, there are studies indicating a potential link between smell identification ability and MCI.


A meta-analysis found that smell identification is impaired in those with MCI compared with healthy older adults. Longitudinal studies also showed that cognitively healthy individuals with smell impairments at baseline subsequently developed MCI in the follow-up.

The evidence suggests that smell identification has the potential to detect and predict the risks of developing dementia in later life.

To the best of our knowledge, there has yet to be any study examining smell function in Singapore’s healthy and/or cognitively impaired community-dwelling older adult population. Mind Science Centre’s study aimed to assess their smell identification ability and associate the outcomes with their cognitive status.

Culture specific smell test developed in NUS

The original nine-item smell test developed by the University of Pennsylvania (UPSIT) included items as liquorice, dill pickle, and skunk. These are not common in Singapore and participants often struggle to recognise and identify them.


To better screen and evaluate smell function in Singapore’s older adult population, our researchers recognised a need to create a localised version of the smell test that is culture-specific to our population. Researchers in NUS developed the Singapore version of the 9-items Smell Test Panel based on a local smell familiarity survey. This includes almond, banana, cinnamon, coconut, lemon, orange, pineapple, rose, and mushroom.

Beyond this study, other clinicians and researchers could also benefit from this locally developed smell test to better screen their patients or research participants.

Participants aged 60 years and above were recruited from a larger epidemiological study titled Community Health and Intergenerational (CHI) study. The smell test and neuropsychological testing are part of a 10-hour assessment done over five separate visits. More details on that can be found in the CHI study protocol.

Smell Tests For Cognitive Impairment

The locally developed nine-item smell test was used to assess smell detection and identification. The test was conducted in an interview format with each odour sample (in total 9) given only once. Between each odour, there was at least a 30-second time interval to prevent sensory fatigue.



For the smell detection task, participants were asked to respond yes or no based on their perception of the presence of an odour. Each successful detection was scored a point.

For the smell identification task, participants were asked to identify the same test odour before choosing through 4 narrated answer choices. If they thought none of the answer choices matched the test odour, they were allowed to describe the odour instead. Each successful identification was scored a point.

Cognitive Function Tests - Testing for Cognitive Impairment

Participants’ cognition was measured with the modified mini-mental state examination (MMSE) scale, clinical dementia rating (CDR) scale, and a validated battery of neurocognitive tests. The protocol is described in more details here.

Diagnosis of the participants’ cognitive status was made at consensus review meetings involving two psychiatrists and a neuropsychologist. Participants were categorised into normal active ageing, MCI, or dementia and further subtyped as amnestic or non-amnestic, and single or multiple domain.

  • NA (normal ageing)
  • naMCI_SD (non-amnestic mild cognitive impairment, single domain)
  • naMCI_MD (non-amnestic mild cognitive impairment, multiple domains)
  • aMCI_SD (amnestic mild cognitive impairment, single domain)
  • aMCI_MD (amnestic mild cognitive impairment, multiple domains)
  • Dementia

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