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Updated: Jun 28, 2025

A Free-breathing fMRI Method to Study Human Olfactory Function
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A Free-breathing fMRI Method to Study Human Olfactory Function

Published on: July 30, 2017

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The role of olfactory dysfunction in mild cognitive impairment and Alzheimer's disease: A meta-analysis

Jaime Bouhaben1, Alice Helena Delgado-Lima1, María Luisa Delgado-Losada1

  • 1Experimental Psychology, Cognitive Processes and Speech Therapy Department, Faculty of Psychology, Complutense University of Madrid, 28223 Pozuelo de Alarcon, Spain.

Archives of Gerontology and Geriatrics
|April 14, 2024
PubMed
Abstract

Insights

Olfactory deficits, particularly in odor identification, are significant in mild cognitive impairment (MCI) and Alzheimer's disease (AD). A simple odor identification test can aid early AD detection in at-risk individuals.

Area of Science:

  • Neuroscience
  • Gerontology
  • Clinical Psychology

Background:

  • Olfactory dysfunction is increasingly recognized as an early indicator of neurodegenerative diseases.
  • Mild cognitive impairment (MCI) and Alzheimer's disease (AD) are associated with sensory deficits, including impaired sense of smell.
  • Understanding the specific olfactory deficits in MCI and AD is crucial for early diagnosis.

Purpose of the Study:

  • To conduct a meta-analysis investigating the association between olfactory deficits and mild cognitive impairment (MCI) and Alzheimer's disease (AD).
  • To quantify the magnitude of olfactory impairment in MCI and AD populations.
  • To explore the relationship between global cognitive status and olfactory deficits.

Main Methods:

  • A comprehensive meta-analysis was performed using data from identified articles.
  • Studies were assessed for methodological quality following PRISMA guidelines.
  • Hedges' g effect size was computed to determine standard mean differences and confidence intervals; moderator analysis was conducted.

Main Results:

  • Odor identification deficits showed larger effect sizes than odor threshold or discrimination in both MCI and AD samples.
  • Moderate effect sizes were observed in olfactory identification (OI) scores in MCI (k = 65).
  • Alzheimer's disease (AD) exhibited moderate to large heterogeneous effects in olfactory identification compared to MCI (k = 61).
  • Global cognitive status was positively related to olfactory identification impairment in both MCI and AD.

Conclusions:

  • Olfactory impairments, especially in odor identification, are notably present in MCI, mirroring deficits seen in AD.
  • Odor identification decline is the primary sensory deficit in MCI, similar to AD.
  • A simple odor identification test is recommended for evaluating individuals at risk for AD, serving as a practical early detection tool.
Keywords:
Alzheimer's diseaseBiomarkerMeta-analysisMild cognitive impairmentOlfactory dysfunction

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