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Updated: Mar 9, 2026
A Free-breathing fMRI Method to Study Human Olfactory Function
Published on: July 30, 2017
A quantitative meta-analysis of olfactory dysfunction in mild cognitive impairment
David R Roalf1, Madelyn J Moberg1, Bruce I Turetsky1
1Department of Psychiatry, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA.
Background:
The connection between Alzheimer's disease (AD) and olfactory deficits is well documented and further, alterations in olfactory functioning may signal declines in functions associated with dementia. The aim of the present comprehensive meta-analysis was to investigate the nature of olfactory deficits in mild cognitive impairment (MCI).
Methods:
Articles were identified through computerised literature search from inception to 30 June 2016 using PubMed, MEDLINE and PsychInfo databases. In order to control for differences in sample size during effect size computation, studies were weighted according to their inverse variance estimates.
Results:
31 articles (62 effects) were identified, which included 1993 MCI patients and 2861 healthy older adults (HOA). Included studies contrasted odour identification, discrimination, detection threshold and/or memory between cases and controls. Moderate to large and heterogeneous effects were seen for olfactory deficits in MCI relative to HOA (d=-0.76, 95% CI -0.87<δ<-0.64). Moderator analysis revealed that tests of odour identification yielded larger effect sizes than those of odour detection threshold or memory. In addition, a potential interaction between age and sex was observed, with male patients carrying a larger burden of olfactory deficit and older female patients performing better on olfactory tests.
Conclusions And Relevance:
Olfactory deficits are present and robust in MCI. Odour identification is most impaired in MCI, which parallels the most prominent sensory deficit seen in AD. As such, a simple-to-administer test of odour identification warrants inclusion in the screening of individuals at risk for developing AD.
Insights
Olfactory deficits are common in mild cognitive impairment (MCI), particularly in odour identification. This suggests smell tests could help screen for Alzheimer's disease (AD) risk.
Area of Science:
- Neuroscience
- Gerontology
- Psychology
Background:
- Alzheimer's disease (AD) is linked to olfactory deficits.
- Olfactory dysfunction may indicate cognitive decline and dementia.
- Mild cognitive impairment (MCI) is a transitional stage between normal aging and dementia.
Purpose of the Study:
- To conduct a meta-analysis on olfactory deficits in MCI.
- To characterize the nature and extent of olfactory impairments in MCI patients.
Main Methods:
- Comprehensive literature search of PubMed, MEDLINE, and PsychInfo databases up to June 2016.
- Meta-analysis of 31 articles including 1993 MCI patients and 2861 healthy older adults (HOA).
- Weighted effect size computation to control for sample size differences.
Main Results:
- Significant, moderate-to-large olfactory deficits found in MCI compared to HOA (d=-0.76).
- Odour identification tests showed larger effect sizes than detection or memory tests.
- Male MCI patients exhibited greater olfactory deficits; older females performed better.
Conclusions:
- Olfactory deficits are a robust finding in MCI.
- Impaired odour identification in MCI mirrors deficits seen in AD.
- Odour identification tests are recommended for screening individuals at risk for AD.
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